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Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

Original post:

Human genetics | biology | Britannica.com

Basic Genetics

Learn.Genetics visitors,

Were asking for your help. For over 20 years, the Learn.Genetics website has provided engaging, multimedia educational materials at no cost.

Learn.Genetics is one of the most-used science websites. Tens of millions of visitors come to our site each year to find the science and health information theyre looking for.

If Learn.Genetics is useful to you, please take a moment to donate even a few dollars from each of our visitors would add up to a significant amount!

Your support will help us keep Learn.Genetics free and available to everyone. It will also help us develop new content for you.

Please help us keep Learn.Genetics going!

Thank you, The Genetic Science Learning Center team creators of Learn.Genetics

Read more:

Basic Genetics

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

Read More on This Topic

genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

Here is the original post:

Human genetics | biology | Britannica.com

Basic Genetics

Learn.Genetics visitors,

Were asking for your help. For over 20 years, the Learn.Genetics website has provided engaging, multimedia educational materials at no cost.

Learn.Genetics is one of the most-used science websites. Tens of millions of visitors come to our site each year to find the science and health information theyre looking for.

If Learn.Genetics is useful to you, please take a moment to donate even a few dollars from each of our visitors would add up to a significant amount!

Your support will help us keep Learn.Genetics free and available to everyone. It will also help us develop new content for you.

Please help us keep Learn.Genetics going!

Thank you, The Genetic Science Learning Center team creators of Learn.Genetics

See the original post:

Basic Genetics

Amazon.com: Human Genetics (9781259700934): Ricki Lewis: Books

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Amazon.com: Human Genetics (9781259700934): Ricki Lewis: Books

Human Genetics – Springer

Human Genetics presents original and timely articles on all aspects of human genetics. Coverage includes gene structure and organization; gene expression; mutation detection and analysis; linkage analysis and genetic mapping; physical mapping; cytogenetics and genomic imaging; genome structure and organization; disease association studies; molecular diagnostics; genetic epidemiology; evolutionary genetics; developmental genetics; genotype-phenotype relationships; molecular genetics of tumorigenesis; genetics of complex diseases and epistatic interactions; ethical, legal and social issues and bioinformatics.

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Human Genetics – Springer

The Dr. John T. Macdonald Foundation Department of Human …

Our mission is to become a world renowned Center of Excellence in the areas of human genetics, genomic research and clinical genomic medicine. Using clinically advanced technology, state-of-the-art equipment and highly trained professionals, we aim to uncover the genetic contributions to disease, apply our findings to better patient care, and educate the geneticists and genomicists of tomorrow.

Established through the generous support of the Dr. John T. Macdonald Foundation, we are committed to the identification of genes and gene networks that cause diseases. We are in an extraordinary period of growth, especially since the completion of the Human Genome Project in 2003. Our recognition spans far beyond traditional single-gene disorders such as sickle cell anemia and cystic fibrosis, and now encompasses knowledge associated with complex conditions such as autism, Alzheimer disease and Parkinson disease.

Like the field of Human Genetics, the University of Miami Miller School of Medicine is undergoing a period of dynamic expansion. Our vision is to manage a state-of-the-art department that will identify disease-causing genes and networks of genes, investigate possible treatments, and redefine our understanding of medicine in the 21st century. We are in an extraordinary period of growth that will position the University of Miami Miller School of Medicine as the leader in genetics and genomics research, education and service in South Florida. Thank you for visiting!

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The Dr. John T. Macdonald Foundation Department of Human …

Alternative medicine – Wikipedia

Alternative medicineAM, complementary and alternative medicine (CAM), complementary medicine, heterodox medicine, integrative medicine (IM), complementary and integrative medicine (CIM), new-age medicine, unconventional medicine, unorthodox medicineHow alternative treatments “work”:a) Misinterpreted natural course the individual gets better without treatment.b) Placebo effect or false treatment effect an individual receives “alternative therapy” and is convinced it will help. The conviction makes them more likely to get better.c) Nocebo effect an individual is convinced that standard treatment will not work, and that alternative treatment will work. This decreases the likelihood standard treatment will work, while the placebo effect of the “alternative” remains. d) No adverse effects Standard treatment is replaced with “alternative” treatment, getting rid of adverse effects, but also of improvement. e) Interference Standard treatment is “complemented” with something that interferes with its effect. This can both cause worse effect, but also decreased (or even increased) side effects, which may be interpreted as “helping”.Researchers such as epidemiologists, clinical statisticians and pharmacologists use clinical trials to tease out such effects, allowing doctors to offer only that which has been shown to work. “Alternative treatments” often refuse to use trials or make it deliberately hard to do so.

Alternative medicine, fringe medicine, pseudomedicine or simply questionable medicine is the use and promotion of practices which are unproven, disproven, impossible to prove, or excessively harmful in relation to their effect in the attempt to achieve the healing effects of medicine. They differ from experimental medicine in that the latter employs responsible investigation, and accepts results that show it to be ineffective. The scientific consensus is that alternative therapies either do not, or cannot, work. In some cases laws of nature are violated by their basic claims; in some the treatment is so much worse that its use is unethical. Alternative practices, products, and therapies range from only ineffective to having known harmful and toxic effects.

Alternative therapies may be credited for perceived improvement through placebo effects, decreased use or effect of medical treatment (and therefore either decreased side effects; or nocebo effects towards standard treatment), or the natural course of the condition or disease. Alternative treatment is not the same as experimental treatment or traditional medicine, although both can be misused in ways that are alternative. Alternative or complementary medicine is dangerous because it may discourage people from getting the best possible treatment, and may lead to a false understanding of the body and of science.

Alternative medicine is used by a significant number of people, though its popularity is often overstated. Large amounts of funding go to testing alternative medicine, with more than US$2.5 billion spent by the United States government alone. Almost none show any effect beyond that of false treatment, and most studies showing any effect have been statistical flukes. Alternative medicine is a highly profitable industry, with a strong lobby. This fact is often overlooked by media or intentionally kept hidden, with alternative practice being portrayed positively when compared to “big pharma”. The lobby has successfully pushed for alternative therapies to be subject to far less regulation than conventional medicine. Alternative therapies may even be allowed to promote use when there is demonstrably no effect, only a tradition of use. Regulation and licensing of alternative medicine and health care providers varies between and within countries. Despite laws making it illegal to market or promote alternative therapies for use in cancer treatment, many practitioners promote them. Alternative medicine is criticized for taking advantage of the weakest members of society. For example, the United States National Institutes of Health department studying alternative medicine, currently named National Center for Complementary and Integrative Health, was established as the Office of Alternative Medicine and was renamed the National Center for Complementary and Alternative Medicine before obtaining its current name. Therapies are often framed as “natural” or “holistic”, in apparent opposition to conventional medicine which is “artificial” and “narrow in scope”, statements which are intentionally misleading. When used together with functional medical treatment, alternative therapies do not “complement” (improve the effect of, or mitigate the side effects of) treatment. Significant drug interactions caused by alternative therapies may instead negatively impact functional treatment, making it less effective, notably in cancer.

Alternative diagnoses and treatments are not part of medicine, or of science-based curricula in medical schools, nor are they used in any practice based on scientific knowledge or experience. Alternative therapies are often based on religious belief, tradition, superstition, belief in supernatural energies, pseudoscience, errors in reasoning, propaganda, fraud, or lies. Alternative medicine is based on misleading statements, quackery, pseudoscience, antiscience, fraud, and poor scientific methodology. Promoting alternative medicine has been called dangerous and unethical. Testing alternative medicine that has no scientific basis has been called a waste of scarce research resources. Critics state that “there is really no such thing as alternative medicine, just medicine that works and medicine that doesn’t”, that the very idea of “alternative” treatments is paradoxical, as any treatment proven to work is by definition “medicine”.

Alternative medicine is defined loosely as a set of products, practices, and theories that are believed or perceived by their users to have the healing effects of medicine,[n 1][n 2] but whose effectiveness has not been clearly established using scientific methods,[n 1][n 3][4][5][6][7] or whose theory and practice is not part of biomedicine,[n 2][n 4][n 5][n 6] or whose theories or practices are directly contradicted by scientific evidence or scientific principles used in biomedicine.[4][5][11] “Biomedicine” or “medicine” is that part of medical science that applies principles of biology, physiology, molecular biology, biophysics, and other natural sciences to clinical practice, using scientific methods to establish the effectiveness of that practice. Unlike medicine,[n 4] an alternative product or practice does not originate from using scientific methods, but may instead be based on hearsay, religion, tradition, superstition, belief in supernatural energies, pseudoscience, errors in reasoning, propaganda, fraud, or other unscientific sources.[n 3][1][4][5]

In General Guidelines for Methodologies on Research and Evaluation of Traditional Medicine, published in 2000 by the World Health Organization (WHO), complementary and alternative medicine were defined as a broad set of health care practices that are not part of that country’s own tradition and are not integrated into the dominant health care system.[12]

The expression also refers to a diverse range of related and unrelated products, practices, and theories ranging from biologically plausible practices and products and practices with some evidence, to practices and theories that are directly contradicted by basic science or clear evidence, and products that have been conclusively proven to be ineffective or even toxic and harmful.[n 2][14][15]

The terms alternative medicine, complementary medicine, integrative medicine, holistic medicine, natural medicine, unorthodox medicine, fringe medicine, unconventional medicine, and new age medicine are used interchangeably as having the same meaning and are almost synonymous in most contexts.[16][17][18][19]

The meaning of the term “alternative” in the expression “alternative medicine”, is not that it is an effective alternative to medical science, although some alternative medicine promoters may use the loose terminology to give the appearance of effectiveness.[4][20] Loose terminology may also be used to suggest meaning that a dichotomy exists when it does not, e.g., the use of the expressions “western medicine” and “eastern medicine” to suggest that the difference is a cultural difference between the Asiatic east and the European west, rather than that the difference is between evidence-based medicine and treatments that do not work.[4]

Complementary medicine (CM) or integrative medicine (IM) is when alternative medicine is used together with functional medical treatment, in a belief that it improves the effect of treatments.[n 7][1][22][23][24] However, significant drug interactions caused by alternative therapies may instead negatively influence treatment, making treatments less effective, notably cancer therapy.[25][26] Both terms refer to use of alternative medical treatments alongside conventional medicine,[27][28][29] an example of which is use of acupuncture (sticking needles in the body to influence the flow of a supernatural energy), along with using science-based medicine, in the belief that the acupuncture increases the effectiveness or “complements” the science-based medicine.[29]

CAM is an abbreviation of the phrase complementary and alternative medicine.[30][31] It has also been called sCAM or SCAM with the addition of “so-called” or “supplements”.[32][33]

Allopathic medicine or allopathy is an expression commonly used by homeopaths and proponents of other forms of alternative medicine to refer to mainstream medicine. It was used to describe the traditional European practice of heroic medicine,[34] but later continued to be used to describe anything that was not homeopathy.[34]

Allopathy refers to the use of pharmacologically active agents or physical interventions to treat or suppress symptoms or pathophysiologic processes of diseases or conditions.[35] The German version of the word, allopathisch, was coined in 1810 by the creator of homeopathy, Samuel Hahnemann (17551843).[36] The word was coined from allo- (different) and -pathic (relating to a disease or to a method of treatment).[37] In alternative medicine circles the expression “allopathic medicine” is still used to refer to “the broad category of medical practice that is sometimes called Western medicine, biomedicine, evidence-based medicine, or modern medicine” (see the article on scientific medicine).[38]

Use of the term remains common among homeopaths and has spread to other alternative medicine practices. The meaning implied by the label has never been accepted by conventional medicine and is considered pejorative.[39] More recently, some sources have used the term “allopathic”, particularly American sources wishing to distinguish between Doctors of Medicine (MD) and Doctors of Osteopathic Medicine (DO) in the United States.[36][40] William Jarvis, an expert on alternative medicine and public health,[41] states that “although many modern therapies can be construed to conform to an allopathic rationale (e.g., using a laxative to relieve constipation), standard medicine has never paid allegiance to an allopathic principle” and that the label “allopath” was from the start “considered highly derisive by regular medicine”.[42]

Many conventional medical treatments do not fit the nominal definition of allopathy, as they seek to prevent illness, or remove its cause.[43][44]

CAM is an abbreviation of complementary and alternative medicine.[30][31] It has also been called sCAM or SCAM with the addition of “so-called” or “supplements”.[32][33] The words balance and holism are often used, claiming to take into account a “whole” person, in contrast to the supposed reductionism of medicine. Due to its many names the field has been criticized for intense rebranding of what are essentially the same practices: as soon as one name is declared synonymous with quackery, a new name is chosen.[16]

Traditional medicine refers to the pre-scientific practices of a certain culture, contrary to what is typically practiced in other cultures where medical science dominates.

“Eastern medicine” typically refers to the traditional medicines of Asia where conventional bio-medicine penetrated much later.

The words balance and holism are often used alongside complementary or integrative medicine, claiming to take into account a “whole” person, in contrast to the supposed reductionism of medicine. Due to its many names the field has been criticized for intense rebranding of what are essentially the same practices.[16]

Prominent members of the science[45][46] and biomedical science community[3] say that it is not meaningful to define an alternative medicine that is separate from a conventional medicine, that the expressions “conventional medicine”, “alternative medicine”, “complementary medicine”, “integrative medicine”, and “holistic medicine” do not refer to any medicine at all.[45][3][46][47]

Others in both the biomedical and CAM communities say that CAM cannot be precisely defined because of the diversity of theories and practices it includes, and because the boundaries between CAM and biomedicine overlap, are porous, and change. The expression “complementary and alternative medicine” (CAM) resists easy definition because the health systems and practices it refers to are diffuse, and its boundaries poorly defined.[14][n 8] Healthcare practices categorized as alternative may differ in their historical origin, theoretical basis, diagnostic technique, therapeutic practice and in their relationship to the medical mainstream. Some alternative therapies, including traditional Chinese medicine (TCM) and Ayurveda, have antique origins in East or South Asia and are entirely alternative medical systems;[52] others, such as homeopathy and chiropractic, have origins in Europe or the United States and emerged in the eighteenth and nineteenth centuries. Some, such as osteopathy and chiropractic, employ manipulative physical methods of treatment; others, such as meditation and prayer, are based on mind-body interventions. Treatments considered alternative in one location may be considered conventional in another.[55] Thus, chiropractic is not considered alternative in Denmark and likewise osteopathic medicine is no longer thought of as an alternative therapy in the United States.[55]

Critics say the expression is deceptive because it implies there is an effective alternative to science-based medicine, and that complementary is deceptive because it implies that the treatment increases the effectiveness of (complements) science-based medicine, while alternative medicines that have been tested nearly always have no measurable positive effect compared to a placebo.[4][56][57][58]

One common feature of all definitions of alternative medicine is its designation as “other than” conventional medicine. For example, the widely referenced descriptive definition of complementary and alternative medicine devised by the US National Center for Complementary and Integrative Health (NCCIH) of the National Institutes of Health (NIH), states that it is “a group of diverse medical and health care systems, practices, and products that are not generally considered part of conventional medicine”.[61] For conventional medical practitioners, it does not necessarily follow that either it or its practitioners would no longer be considered alternative.[n 9]

Some definitions seek to specify alternative medicine in terms of its social and political marginality to mainstream healthcare.[64] This can refer to the lack of support that alternative therapies receive from the medical establishment and related bodies regarding access to research funding, sympathetic coverage in the medical press, or inclusion in the standard medical curriculum.[64] In 1993, the British Medical Association (BMA), one among many professional organizations who have attempted to define alternative medicine, stated that it[n 10] referred to “…those forms of treatment which are not widely used by the conventional healthcare professions, and the skills of which are not taught as part of the undergraduate curriculum of conventional medical and paramedical healthcare courses”.[65] In a US context, an influential definition coined in 1993 by the Harvard-based physician,[66] David M. Eisenberg,[67] characterized alternative medicine “as interventions neither taught widely in medical schools nor generally available in US hospitals”.[68] These descriptive definitions are inadequate in the present-day when some conventional doctors offer alternative medical treatments and CAM introductory courses or modules can be offered as part of standard undergraduate medical training;[69] alternative medicine is taught in more than 50 per cent of US medical schools and increasingly US health insurers are willing to provide reimbursement for CAM therapies. In 1999, 7.7% of US hospitals reported using some form of CAM therapy; this proportion had risen to 37.7% by 2008.[71]

An expert panel at a conference hosted in 1995 by the US Office for Alternative Medicine (OAM),[72][n 11] devised a theoretical definition[72] of alternative medicine as “a broad domain of healing resources… other than those intrinsic to the politically dominant health system of a particular society or culture in a given historical period”.[74] This definition has been widely adopted by CAM researchers,[72] cited by official government bodies such as the UK Department of Health,[75] attributed as the definition used by the Cochrane Collaboration,[76] and, with some modification,[dubious discuss] was preferred in the 2005 consensus report of the US Institute of Medicine, Complementary and Alternative Medicine in the United States.[n 2]

The 1995 OAM conference definition, an expansion of Eisenberg’s 1993 formulation, is silent regarding questions of the medical effectiveness of alternative therapies.[77] Its proponents hold that it thus avoids relativism about differing forms of medical knowledge and, while it is an essentially political definition, this should not imply that the dominance of mainstream biomedicine is solely due to political forces.[77] According to this definition, alternative and mainstream medicine can only be differentiated with reference to what is “intrinsic to the politically dominant health system of a particular society of culture”.[78] However, there is neither a reliable method to distinguish between cultures and subcultures, nor to attribute them as dominant or subordinate, nor any accepted criteria to determine the dominance of a cultural entity.[78] If the culture of a politically dominant healthcare system is held to be equivalent to the perspectives of those charged with the medical management of leading healthcare institutions and programs, the definition fails to recognize the potential for division either within such an elite or between a healthcare elite and the wider population.[78]

Normative definitions distinguish alternative medicine from the biomedical mainstream in its provision of therapies that are unproven, unvalidated, or ineffective and support of theories with no recognized scientific basis. These definitions characterize practices as constituting alternative medicine when, used independently or in place of evidence-based medicine, they are put forward as having the healing effects of medicine, but are not based on evidence gathered with the scientific method.[1][3][27][28][61][80] Exemplifying this perspective, a 1998 editorial co-authored by Marcia Angell, a former editor of The New England Journal of Medicine, argued that:

It is time for the scientific community to stop giving alternative medicine a free ride. There cannot be two kinds of medicine conventional and alternative. There is only medicine that has been adequately tested and medicine that has not, medicine that works and medicine that may or may not work. Once a treatment has been tested rigorously, it no longer matters whether it was considered alternative at the outset. If it is found to be reasonably safe and effective, it will be accepted. But assertions, speculation, and testimonials do not substitute for evidence. Alternative treatments should be subjected to scientific testing no less rigorous than that required for conventional treatments.[3]

This line of division has been subject to criticism, however, as not all forms of standard medical practice have adequately demonstrated evidence of benefit,[n 4][81] and it is also unlikely in most instances that conventional therapies, if proven to be ineffective, would ever be classified as CAM.[72]

Similarly, the public information website maintained by the National Health and Medical Research Council (NHMRC) of the Commonwealth of Australia uses the acronym “CAM” for a wide range of health care practices, therapies, procedures and devices not within the domain of conventional medicine. In the Australian context this is stated to include acupuncture; aromatherapy; chiropractic; homeopathy; massage; meditation and relaxation therapies; naturopathy; osteopathy; reflexology, traditional Chinese medicine; and the use of vitamin supplements.[83]

The Danish National Board of Health’s “Council for Alternative Medicine” (Sundhedsstyrelsens Rd for Alternativ Behandling (SRAB)), an independent institution under the National Board of Health (Danish: Sundhedsstyrelsen), uses the term “alternative medicine” for:

Proponents of an evidence-base for medicine[n 12][86][87][88][89] such as the Cochrane Collaboration (founded in 1993 and from 2011 providing input for WHO resolutions) take a position that all systematic reviews of treatments, whether “mainstream” or “alternative”, ought to be held to the current standards of scientific method.[90] In a study titled Development and classification of an operational definition of complementary and alternative medicine for the Cochrane Collaboration (2011) it was proposed that indicators that a therapy is accepted include government licensing of practitioners, coverage by health insurance, statements of approval by government agencies, and recommendation as part of a practice guideline; and that if something is currently a standard, accepted therapy, then it is not likely to be widely considered as CAM.[72]

Alternative medicine consists of a wide range of health care practices, products, and therapies. The shared feature is a claim to heal that is not based on the scientific method. Alternative medicine practices are diverse in their foundations and methodologies.[61] Alternative medicine practices may be classified by their cultural origins or by the types of beliefs upon which they are based.[1][4][11][61] Methods may incorporate or be based on traditional medicinal practices of a particular culture, folk knowledge, superstition, spiritual beliefs, belief in supernatural energies (antiscience), pseudoscience, errors in reasoning, propaganda, fraud, new or different concepts of health and disease, and any bases other than being proven by scientific methods.[1][4][5][11] Different cultures may have their own unique traditional or belief based practices developed recently or over thousands of years, and specific practices or entire systems of practices.

Alternative medicine, such as using naturopathy or homeopathy in place of conventional medicine, is based on belief systems not grounded in science.[61]

Alternative medical systems may be based on traditional medicine practices, such as traditional Chinese medicine (TCM), Ayurveda in India, or practices of other cultures around the world.[61] Some useful applications of traditional medicines have been researched and accepted within ordinary medicine, however the underlying belief systems are seldom scientific and are not accepted.

Traditional medicine is considered alternative when it is used outside its home region; or when it is used together with or instead of known functional treatment; or when it can be reasonably expected that the patient or practitioner knows or should know that it will not work such as knowing that the practice is based on superstition.

Since ancient times, in many parts of the world a number of herbs reputed to possess abortifacient properties have been used in folk medicine. Among these are: tansy, pennyroyal, black cohosh, and the now-extinct silphium.[101]:4447, 6263, 15455, 23031 Historian of science Ann Hibner Koblitz has written of the probable protoscientific origins of this folk knowledge in observation of farm animals. Women who knew that grazing on certain plants would cause an animal to abort (with negative economic consequences for the farm) would be likely to try out those plants on themselves in order to avoid an unwanted pregnancy.[102]:120

However, modern users of these plants often lack knowledge of the proper preparation and dosage. The historian of medicine John Riddle has spoken of the “broken chain of knowledge” caused by urbanization and modernization,[101]:167205 and Koblitz has written that “folk knowledge about effective contraception techniques often disappears over time or becomes inextricably mixed with useless or harmful practices.”[102]:vii The ill-informed or indiscriminant use of herbs as abortifacients can cause serious and even lethal side-effects.[103][104]

Bases of belief may include belief in existence of supernatural energies undetected by the science of physics, as in biofields, or in belief in properties of the energies of physics that are inconsistent with the laws of physics, as in energy medicine.[61]

Substance based practices use substances found in nature such as herbs, foods, non-vitamin supplements and megavitamins, animal and fungal products, and minerals, including use of these products in traditional medical practices that may also incorporate other methods.[61][119][120] Examples include healing claims for nonvitamin supplements, fish oil, Omega-3 fatty acid, glucosamine, echinacea, flaxseed oil, and ginseng.[121] Herbal medicine, or phytotherapy, includes not just the use of plant products, but may also include the use of animal and mineral products.[119] It is among the most commercially successful branches of alternative medicine, and includes the tablets, powders and elixirs that are sold as “nutritional supplements”.[119] Only a very small percentage of these have been shown to have any efficacy, and there is little regulation as to standards and safety of their contents.[119] This may include use of known toxic substances, such as use of the poison lead in traditional Chinese medicine.[121]

A US agency, National Center on Complementary and Integrative Health (NCCIH), has created a classification system for branches of complementary and alternative medicine that divides them into five major groups. These groups have some overlap, and distinguish two types of energy medicine: veritable which involves scientifically observable energy (including magnet therapy, colorpuncture and light therapy) and putative, which invokes physically undetectable or unverifiable energy.[125] None of these energies have any evidence to support that they effect the body in any positive or health promoting way.[34]

The history of alternative medicine may refer to the history of a group of diverse medical practices that were collectively promoted as “alternative medicine” beginning in the 1970s, to the collection of individual histories of members of that group, or to the history of western medical practices that were labeled “irregular practices” by the western medical establishment.[4][126][127][128][129] It includes the histories of complementary medicine and of integrative medicine. Before the 1970s, western practitioners that were not part of the increasingly science-based medical establishment were referred to “irregular practitioners”, and were dismissed by the medical establishment as unscientific and as practicing quackery.[126][127] Until the 1970s, irregular practice became increasingly marginalized as quackery and fraud, as western medicine increasingly incorporated scientific methods and discoveries, and had a corresponding increase in success of its treatments.[128] In the 1970s, irregular practices were grouped with traditional practices of nonwestern cultures and with other unproven or disproven practices that were not part of biomedicine, with the entire group collectively marketed and promoted under the single expression “alternative medicine”.[4][126][127][128][130]

Use of alternative medicine in the west began to rise following the counterculture movement of the 1960s, as part of the rising new age movement of the 1970s.[4][131][132] This was due to misleading mass marketing of “alternative medicine” being an effective “alternative” to biomedicine, changing social attitudes about not using chemicals and challenging the establishment and authority of any kind, sensitivity to giving equal measure to beliefs and practices of other cultures (cultural relativism), and growing frustration and desperation by patients about limitations and side effects of science-based medicine.[4][127][128][129][130][132][133] At the same time, in 1975, the American Medical Association, which played the central role in fighting quackery in the United States, abolished its quackery committee and closed down its Department of Investigation.[126]:xxi[133] By the early to mid 1970s the expression “alternative medicine” came into widespread use, and the expression became mass marketed as a collection of “natural” and effective treatment “alternatives” to science-based biomedicine.[4][133][134][135] By 1983, mass marketing of “alternative medicine” was so pervasive that the British Medical Journal (BMJ) pointed to “an apparently endless stream of books, articles, and radio and television programmes urge on the public the virtues of (alternative medicine) treatments ranging from meditation to drilling a hole in the skull to let in more oxygen”.[133]

Mainly as a result of reforms following the Flexner Report of 1910[136] medical education in established medical schools in the US has generally not included alternative medicine as a teaching topic.[n 14] Typically, their teaching is based on current practice and scientific knowledge about: anatomy, physiology, histology, embryology, neuroanatomy, pathology, pharmacology, microbiology and immunology.[138] Medical schools’ teaching includes such topics as doctor-patient communication, ethics, the art of medicine,[139] and engaging in complex clinical reasoning (medical decision-making).[140] Writing in 2002, Snyderman and Weil remarked that by the early twentieth century the Flexner model had helped to create the 20th-century academic health center, in which education, research, and practice were inseparable. While this had much improved medical practice by defining with increasing certainty the pathophysiological basis of disease, a single-minded focus on the pathophysiological had diverted much of mainstream American medicine from clinical conditions that were not well understood in mechanistic terms, and were not effectively treated by conventional therapies.[141]

By 2001 some form of CAM training was being offered by at least 75 out of 125 medical schools in the US.[142] Exceptionally, the School of Medicine of the University of Maryland, Baltimore includes a research institute for integrative medicine (a member entity of the Cochrane Collaboration).[90][143] Medical schools are responsible for conferring medical degrees, but a physician typically may not legally practice medicine until licensed by the local government authority. Licensed physicians in the US who have attended one of the established medical schools there have usually graduated Doctor of Medicine (MD).[144] All states require that applicants for MD licensure be graduates of an approved medical school and complete the United States Medical Licensing Exam (USMLE).[144]

There is a general scientific consensus that alternative therapies lack the requisite scientific validation, and their effectiveness is either unproved or disproved.[1][4][145][146] Many of the claims regarding the efficacy of alternative medicines are controversial, since research on them is frequently of low quality and methodologically flawed. Selective publication bias, marked differences in product quality and standardisation, and some companies making unsubstantiated claims call into question the claims of efficacy of isolated examples where there is evidence for alternative therapies.[148]

The Scientific Review of Alternative Medicine points to confusions in the general population a person may attribute symptomatic relief to an otherwise-ineffective therapy just because they are taking something (the placebo effect); the natural recovery from or the cyclical nature of an illness (the regression fallacy) gets misattributed to an alternative medicine being taken; a person not diagnosed with science-based medicine may never originally have had a true illness diagnosed as an alternative disease category.[149]

Edzard Ernst characterized the evidence for many alternative techniques as weak, nonexistent, or negative[150] and in 2011 published his estimate that about 7.4% were based on “sound evidence”, although he believes that may be an overestimate.[151] Ernst has concluded that 95% of the alternative treatments he and his team studied, including acupuncture, herbal medicine, homeopathy, and reflexology, are “statistically indistinguishable from placebo treatments”, but he also believes there is something that conventional doctors can usefully learn from the chiropractors and homeopath: this is the therapeutic value of the placebo effect, one of the strangest phenomena in medicine.[152][153]

In 2003, a project funded by the CDC identified 208 condition-treatment pairs, of which 58% had been studied by at least one randomized controlled trial (RCT), and 23% had been assessed with a meta-analysis.[154] According to a 2005 book by a US Institute of Medicine panel, the number of RCTs focused on CAM has risen dramatically.

As of 2005[update], the Cochrane Library had 145 CAM-related Cochrane systematic reviews and 340 non-Cochrane systematic reviews. An analysis of the conclusions of only the 145 Cochrane reviews was done by two readers. In 83% of the cases, the readers agreed. In the 17% in which they disagreed, a third reader agreed with one of the initial readers to set a rating. These studies found that, for CAM, 38.4% concluded positive effect or possibly positive (12.4%), 4.8% concluded no effect, 0.7% concluded harmful effect, and 56.6% concluded insufficient evidence. An assessment of conventional treatments found that 41.3% concluded positive or possibly positive effect, 20% concluded no effect, 8.1% concluded net harmful effects, and 21.3% concluded insufficient evidence. However, the CAM review used the more developed 2004 Cochrane database, while the conventional review used the initial 1998 Cochrane database.

In the same way as for conventional therapies, drugs, and interventions, it can be difficult to test the efficacy of alternative medicine in clinical trials. In instances where an established, effective, treatment for a condition is already available, the Helsinki Declaration states that withholding such treatment is unethical in most circumstances. Use of standard-of-care treatment in addition to an alternative technique being tested may produce confounded or difficult-to-interpret results.[156]

Cancer researcher Andrew J. Vickers has stated:

Contrary to much popular and scientific writing, many alternative cancer treatments have been investigated in good-quality clinical trials, and they have been shown to be ineffective. The label “unproven” is inappropriate for such therapies; it is time to assert that many alternative cancer therapies have been “disproven”.[157]

A research methods expert and author of Snake Oil Science, R. Barker Bausell, has stated that “it’s become politically correct to investigate nonsense.”[158] There are concerns that just having NIH support is being used to give unfounded “legitimacy to treatments that are not legitimate.”[159]

Use of placebos to achieve a placebo effect in integrative medicine has been criticized as, “…diverting research time, money, and other resources from more fruitful lines of investigation in order to pursue a theory that has no basis in biology.”[57][58]

Another critic has argued that academic proponents of integrative medicine sometimes recommend misleading patients by using known placebo treatments to achieve a placebo effect.[n 15] However, a 2010 survey of family physicians found that 56% of respondents said they had used a placebo in clinical practice as well. Eighty-five percent of respondents believed placebos can have both psychological and physical benefits.[161]

Integrative medicine has been criticized in that its practitioners, trained in science-based medicine, deliberately mislead patients by pretending placebos are not. “quackademic medicine” is a pejorative term used for integrative medicine, which medical professionals consider an infiltration of quackery into academic science-based medicine.[58]

An analysis of trends in the criticism of complementary and alternative medicine (CAM) in five prestigious American medical journals during the period of reorganization within medicine (19651999) was reported as showing that the medical profession had responded to the growth of CAM in three phases, and that in each phase, changes in the medical marketplace had influenced the type of response in the journals.[162] Changes included relaxed medical licensing, the development of managed care, rising consumerism, and the establishment of the USA Office of Alternative Medicine (later National Center for Complementary and Alternative Medicine, currently National Center for Complementary and Integrative Health).[n 16] In the “condemnation” phase, from the late 1960s to the early 1970s, authors had ridiculed, exaggerated the risks, and petitioned the state to contain CAM; in the “reassessment” phase (mid-1970s through early 1990s), when increased consumer utilization of CAM was prompting concern, authors had pondered whether patient dissatisfaction and shortcomings in conventional care contributed to the trend; in the “integration” phase of the 1990s physicians began learning to work around or administer CAM, and the subjugation of CAM to scientific scrutiny had become the primary means of control.[citation needed]

Practitioners of complementary medicine usually discuss and advise patients as to available alternative therapies. Patients often express interest in mind-body complementary therapies because they offer a non-drug approach to treating some health conditions.[164]

In addition to the social-cultural underpinnings of the popularity of alternative medicine, there are several psychological issues that are critical to its growth. One of the most critical is the placebo effect a well-established observation in medicine.[165] Related to it are similar psychological effects, such as the will to believe,[166] cognitive biases that help maintain self-esteem and promote harmonious social functioning,[166] and the post hoc, ergo propter hoc fallacy.[166]

The popularity of complementary & alternative medicine (CAM) may be related to other factors that Edzard Ernst mentioned in an interview in The Independent:

Why is it so popular, then? Ernst blames the providers, customers and the doctors whose neglect, he says, has created the opening into which alternative therapists have stepped. “People are told lies. There are 40 million websites and 39.9 million tell lies, sometimes outrageous lies. They mislead cancer patients, who are encouraged not only to pay their last penny but to be treated with something that shortens their lives. “At the same time, people are gullible. It needs gullibility for the industry to succeed. It doesn’t make me popular with the public, but it’s the truth.[167]

Paul Offit proposed that “alternative medicine becomes quackery” in four ways: by recommending against conventional therapies that are helpful, promoting potentially harmful therapies without adequate warning, draining patients’ bank accounts, or by promoting “magical thinking.”[45]

Authors have speculated on the socio-cultural and psychological reasons for the appeal of alternative medicines among the minority using them in lieu of conventional medicine. There are several socio-cultural reasons for the interest in these treatments centered on the low level of scientific literacy among the public at large and a concomitant increase in antiscientific attitudes and new age mysticism.[166] Related to this are vigorous marketing[168] of extravagant claims by the alternative medical community combined with inadequate media scrutiny and attacks on critics.[166][169]

There is also an increase in conspiracy theories toward conventional medicine and pharmaceutical companies, mistrust of traditional authority figures, such as the physician, and a dislike of the current delivery methods of scientific biomedicine, all of which have led patients to seek out alternative medicine to treat a variety of ailments.[169] Many patients lack access to contemporary medicine, due to a lack of private or public health insurance, which leads them to seek out lower-cost alternative medicine.[170] Medical doctors are also aggressively marketing alternative medicine to profit from this market.[168]

Patients can be averse to the painful, unpleasant, and sometimes-dangerous side effects of biomedical treatments. Treatments for severe diseases such as cancer and HIV infection have well-known, significant side-effects. Even low-risk medications such as antibiotics can have potential to cause life-threatening anaphylactic reactions in a very few individuals. Many medications may cause minor but bothersome symptoms such as cough or upset stomach. In all of these cases, patients may be seeking out alternative treatments to avoid the adverse effects of conventional treatments.[166][169]

Complementary and alternative medicine (CAM) has been described as a broad domain of healing resources that encompasses all health systems, modalities, and practices and their accompanying theories and beliefs, other than those intrinsic to the politically dominant health system of a particular society or culture in a given historical period. CAM includes all such practices and ideas self-defined by their users as preventing or treating illness or promoting health and well-being. Boundaries within CAM and between the CAM domain and that of the dominant system are not always sharp or fixed.[72][dubious discuss]

According to recent research, the increasing popularity of the CAM needs to be explained by moral convictions or lifestyle choices rather than by economic reasoning.[171]

In developing nations, access to essential medicines is severely restricted by lack of resources and poverty. Traditional remedies, often closely resembling or forming the basis for alternative remedies, may comprise primary healthcare or be integrated into the healthcare system. In Africa, traditional medicine is used for 80% of primary healthcare, and in developing nations as a whole over one-third of the population lack access to essential medicines.[172]

Some have proposed adopting a prize system to reward medical research.[173] However, public funding for research exists. Increasing the funding for research on alternative medicine techniques is the purpose of the US National Center for Complementary and Alternative Medicine. NCCIH and its predecessor, the Office of Alternative Medicine, have spent more than US$2.5 billion on such research since 1992; this research has largely not demonstrated the efficacy of alternative treatments.[158][174][175][176]

That alternative medicine has been on the rise “in countries where Western science and scientific method generally are accepted as the major foundations for healthcare, and ‘evidence-based’ practice is the dominant paradigm” was described as an “enigma” in the Medical Journal of Australia.[177]

In the United States, the 1974 Child Abuse Prevention and Treatment Act (CAPTA) required that for states to receive federal money, they had to grant religious exemptions to child neglect and abuse laws regarding religion-based healing practices.[178] Thirty-one states have child-abuse religious exemptions.[179]

The use of alternative medicine in the US has increased,[1][180] with a 50 percent increase in expenditures and a 25 percent increase in the use of alternative therapies between 1990 and 1997 in America.[180] Americans spend many billions on the therapies annually.[180] Most Americans used CAM to treat and/or prevent musculoskeletal conditions or other conditions associated with chronic or recurring pain.[170] In America, women were more likely than men to use CAM, with the biggest difference in use of mind-body therapies including prayer specifically for health reasons”.[170] In 2008, more than 37% of American hospitals offered alternative therapies, up from 27 percent in 2005, and 25% in 2004.[181][182] More than 70% of the hospitals offering CAM were in urban areas.[182]

A survey of Americans found that 88 percent thought that “there are some good ways of treating sickness that medical science does not recognize”.[1] Use of magnets was the most common tool in energy medicine in America, and among users of it, 58 percent described it as at least “sort of scientific”, when it is not at all scientific.[1] In 2002, at least 60 percent of US medical schools have at least some class time spent teaching alternative therapies.[1] “Therapeutic touch”, was taught at more than 100 colleges and universities in 75 countries before the practice was debunked by a nine-year-old child for a school science project.[1][118]

The most common CAM therapies used in the US in 2002 were prayer (45%), herbalism (19%), breathing meditation (12%), meditation (8%), chiropractic medicine (8%), yoga (56%), body work (5%), diet-based therapy (4%), progressive relaxation (3%), mega-vitamin therapy (3%) and Visualization (2%)[170][183]

In Britain, the most often used alternative therapies were Alexander technique, Aromatherapy, Bach and other flower remedies, Body work therapies including massage, Counseling stress therapies, hypnotherapy, Meditation, Reflexology, Shiatsu, Ayurvedic medicine, Nutritional medicine, and Yoga.[184] Ayurvedic medicine remedies are mainly plant based with some use of animal materials. Safety concerns include the use of herbs containing toxic compounds and the lack of quality control in Ayurvedic facilities.[112][114]

According to the National Health Service (England), the most commonly used complementary and alternative medicines (CAM) supported by the NHS in the UK are: acupuncture, aromatherapy, chiropractic, homeopathy, massage, osteopathy and clinical hypnotherapy.[186]

Complementary therapies are often used in palliative care or by practitioners attempting to manage chronic pain in patients. Integrative medicine is considered more acceptable in the interdisciplinary approach used in palliative care than in other areas of medicine. “From its early experiences of care for the dying, palliative care took for granted the necessity of placing patient values and lifestyle habits at the core of any design and delivery of quality care at the end of life. If the patient desired complementary therapies, and as long as such treatments provided additional support and did not endanger the patient, they were considered acceptable.”[187] The non-pharmacologic interventions of complementary medicine can employ mind-body interventions designed to “reduce pain and concomitant mood disturbance and increase quality of life.”[188]

In Austria and Germany complementary and alternative medicine is mainly in the hands of doctors with MDs,[30] and half or more of the American alternative practitioners are licensed MDs.[189] In Germany herbs are tightly regulated: half are prescribed by doctors and covered by health insurance.[190]

Some professions of complementary/traditional/alternative medicine, such as chiropractic, have achieved full regulation in North America and other parts of the world and are regulated in a manner similar to that governing science-based medicine. In contrast, other approaches may be partially recognized and others have no regulation at all. Regulation and licensing of alternative medicine ranges widely from country to country, and state to state.

Government bodies in the US and elsewhere have published information or guidance about alternative medicine. The U.S. Food and Drug Administration (FDA), has issued online warnings for consumers about medication health fraud.[192] This includes a section on Alternative Medicine Fraud,[193] such as a warning that Ayurvedic products generally have not been approved by the FDA before marketing.[194]

Many of the claims regarding the safety and efficacy of alternative medicine are controversial. Some alternative treatments have been associated with unexpected side effects, which can be fatal.[195]

A commonly voiced concerns about complementary alternative medicine (CAM) is the way it’s regulated. There have been significant developments in how CAMs should be assessed prior to re-sale in the United Kingdom and the European Union (EU) in the last 2 years. Despite this, it has been suggested that current regulatory bodies have been ineffective in preventing deception of patients as many companies have re-labelled their drugs to avoid the new laws.[196] There is no general consensus about how to balance consumer protection (from false claims, toxicity, and advertising) with freedom to choose remedies.

Advocates of CAM suggest that regulation of the industry will adversely affect patients looking for alternative ways to manage their symptoms, even if many of the benefits may represent the placebo affect.[197] Some contend that alternative medicines should not require any more regulation than over-the-counter medicines that can also be toxic in overdose (such as paracetamol).[198]

Forms of alternative medicine that are biologically active can be dangerous even when used in conjunction with conventional medicine. Examples include immuno-augmentation therapy, shark cartilage, bioresonance therapy, oxygen and ozone therapies, and insulin potentiation therapy. Some herbal remedies can cause dangerous interactions with chemotherapy drugs, radiation therapy, or anesthetics during surgery, among other problems.[31] An anecdotal example of these dangers was reported by Associate Professor Alastair MacLennan of Adelaide University, Australia regarding a patient who almost bled to death on the operating table after neglecting to mention that she had been taking “natural” potions to “build up her strength” before the operation, including a powerful anticoagulant that nearly caused her death.[199]

To ABC Online, MacLennan also gives another possible mechanism:

And lastly [sic] there’s the cynicism and disappointment and depression that some patients get from going on from one alternative medicine to the next, and they find after three months the placebo effect wears off, and they’re disappointed and they move on to the next one, and they’re disappointed and disillusioned, and that can create depression and make the eventual treatment of the patient with anything effective difficult, because you may not get compliance, because they’ve seen the failure so often in the past.[200]

Conventional treatments are subjected to testing for undesired side-effects, whereas alternative treatments, in general, are not subjected to such testing at all. Any treatment whether conventional or alternative that has a biological or psychological effect on a patient may also have potential to possess dangerous biological or psychological side-effects. Attempts to refute this fact with regard to alternative treatments sometimes use the appeal to nature fallacy, i.e., “That which is natural cannot be harmful.” Specific groups of patients such as patients with impaired hepatic or renal function are more susceptible to side effects of alternative remedies.[201][202]

An exception to the normal thinking regarding side-effects is Homeopathy. Since 1938, the U.S. Food and Drug Administration (FDA) has regulated homeopathic products in “several significantly different ways from other drugs.”[203] Homeopathic preparations, termed “remedies”, are extremely dilute, often far beyond the point where a single molecule of the original active (and possibly toxic) ingredient is likely to remain. They are, thus, considered safe on that count, but “their products are exempt from good manufacturing practice requirements related to expiration dating and from finished product testing for identity and strength”, and their alcohol concentration may be much higher than allowed in conventional drugs.[203]

Those having experienced or perceived success with one alternative therapy for a minor ailment may be convinced of its efficacy and persuaded to extrapolate that success to some other alternative therapy for a more serious, possibly life-threatening illness.[204] For this reason, critics argue that therapies that rely on the placebo effect to define success are very dangerous. According to mental health journalist Scott Lilienfeld in 2002, “unvalidated or scientifically unsupported mental health practices can lead individuals to forgo effective treatments” and refers to this as “opportunity cost”. Individuals who spend large amounts of time and money on ineffective treatments may be left with precious little of either, and may forfeit the opportunity to obtain treatments that could be more helpful. In short, even innocuous treatments can indirectly produce negative outcomes.[205] Between 2001 and 2003, four children died in Australia because their parents chose ineffective naturopathic, homeopathic, or other alternative medicines and diets rather than conventional therapies.[206]

There have always been “many therapies offered outside of conventional cancer treatment centers and based on theories not found in biomedicine. These alternative cancer cures have often been described as ‘unproven,’ suggesting that appropriate clinical trials have not been conducted and that the therapeutic value of the treatment is unknown.” However, “many alternative cancer treatments have been investigated in good-quality clinical trials, and they have been shown to be ineffective….The label ‘unproven’ is inappropriate for such therapies; it is time to assert that many alternative cancer therapies have been ‘disproven’.”[157]

Edzard Ernst has stated:

…any alternative cancer cure is bogus by definition. There will never be an alternative cancer cure. Why? Because if something looked halfway promising, then mainstream oncology would scrutinize it, and if there is anything to it, it would become mainstream almost automatically and very quickly. All curative “alternative cancer cures” are based on false claims, are bogus, and, I would say, even criminal.[207]

“CAM”, meaning “complementary and alternative medicine”, is not as well researched as conventional medicine, which undergoes intense research before release to the public.[208] Funding for research is also sparse making it difficult to do further research for effectiveness of CAM.[209] Most funding for CAM is funded by government agencies.[208] Proposed research for CAM are rejected by most private funding agencies because the results of research are not reliable.[208] The research for CAM has to meet certain standards from research ethics committees, which most CAM researchers find almost impossible to meet.[208] Even with the little research done on it, CAM has not been proven to be effective.[210]

Steven Novella, a neurologist at Yale School of Medicine, wrote that government funded studies of integrating alternative medicine techniques into the mainstream are “used to lend an appearance of legitimacy to treatments that are not legitimate.”[159] Marcia Angell considered that critics felt that healthcare practices should be classified based solely on scientific evidence, and if a treatment had been rigorously tested and found safe and effective, science-based medicine will adopt it regardless of whether it was considered “alternative” to begin with.[3] It is possible for a method to change categories (proven vs. unproven), based on increased knowledge of its effectiveness or lack thereof. A prominent supporter of this position is George D. Lundberg, former editor of the Journal of the American Medical Association (JAMA).[47]

Writing in 1999 in CA: A Cancer Journal for Clinicians Barrie R. Cassileth mentioned a 1997 letter to the US Senate Subcommittee on Public Health and Safety, which had deplored the lack of critical thinking and scientific rigor in OAM-supported research, had been signed by four Nobel Laureates and other prominent scientists. (This was supported by the National Institutes of Health (NIH).)[211]

In March 2009 a staff writer for the Washington Post reported that the impending national discussion about broadening access to health care, improving medical practice and saving money was giving a group of scientists an opening to propose shutting down the National Center for Complementary and Alternative Medicine. They quoted one of these scientists, Steven Salzberg, a genome researcher and computational biologist at the University of Maryland, as saying “One of our concerns is that NIH is funding pseudoscience.” They noted that the vast majority of studies were based on fundamental misunderstandings of physiology and disease, and had shown little or no effect.[159]

Writers such as Carl Sagan, a noted astrophysicist, advocate of scientific skepticism and the author of The Demon-Haunted World: Science as a Candle in the Dark (1996), have lambasted the lack of empirical evidence to support the existence of the putative energy fields on which these therapies are predicated.

Sampson has also pointed out that CAM tolerated contradiction without thorough reason and experiment.[212] Barrett has pointed out that there is a policy at the NIH of never saying something doesn’t work only that a different version or dose might give different results.[158] Barrett also expressed concern that, just because some “alternatives” have merit, there is the impression that the rest deserve equal consideration and respect even though most are worthless, since they are all classified under the one heading of alternative medicine.[213]

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82-year-old polio survivor Mona Randolph uses one of only three “iron lungs” known to still be in use in the U.S. The iron lung, which was invented in 1920s, was often used on polio patients who were unable to breathe after the virus paralyzed muscle groups in the chest. Six nights a week, Randolph sleeps up to her neck in a noisy, airtight, 75-year-old iron tube.

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Category:Alternative medicine – Wikipedia

Alternative medicine encompasses methods used in both complementary medicine and alternative medicine, known collectively as complementary and alternative medicine (CAM). These methods are used in place of (“alternative to”), or in addition to (“complementary to”), conventional medical treatments. The terms are primarily used in the western world, and include several traditional medicine techniques practiced throughout the world.

If you add something to this category it should also be added to list of forms of alternative medicine.

This category has the following 10 subcategories, out of 10 total.

The following 106 pages are in this category, out of 106 total. This list may not reflect recent changes (learn more).

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Category:Alternative medicine – Wikipedia

Human mitochondrial genetics – Wikipedia

Human mitochondrial genetics is the study of the genetics of human mitochondrial DNA (the DNA contained in human mitochondria). The human mitochondrial genome is the entirety of hereditary information contained in human mitochondria. Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the “powerhouses” of the cell.

Mitochondrial DNA (mtDNA) is not transmitted through nuclear DNA (nDNA). In humans, as in most multicellular organisms, mitochondrial DNA is inherited only from the mother’s ovum. There are theories, however, that paternal mtDNA transmission in humans can occur under certain circumstances.[1]

Mitochondrial inheritance is therefore non-Mendelian, as Mendelian inheritance presumes that half the genetic material of a fertilized egg (zygote) derives from each parent.

Eighty percent of mitochondrial DNA codes for mitochondrial RNA, and therefore most mitochondrial DNA mutations lead to functional problems, which may be manifested as muscle disorders (myopathies).

Because they provide 30 molecules of ATP per glucose molecule in contrast to the 2 ATP molecules produced by glycolysis, mitochondria are essential to all higher organisms for sustaining life. The mitochondrial diseases are genetic disorders carried in mitochondrial DNA, or nuclear DNA coding for mitochondrial components. Slight problems with any one of the numerous enzymes used by the mitochondria can be devastating to the cell, and in turn, to the organism.

In humans, mitochondrial DNA (mtDNA) forms closed circular molecules that contain 16,569[2][3] DNA base pairs,[4] with each such molecule normally containing a full set of the mitochondrial genes. Each human mitochondrion contains, on average, approximately 5 such mtDNA molecules, with the quantity ranging between 1 and 15.[4] Each human cell contains approximately 100 mitochondria, giving a total number of mtDNA molecules per human cell of approximately 500.[4]

Because mitochondrial diseases (diseases due to malfunction of mitochondria) can be inherited both maternally and through chromosomal inheritance, the way in which they are passed on from generation to generation can vary greatly depending on the disease. Mitochondrial genetic mutations that occur in the nuclear DNA can occur in any of the chromosomes (depending on the species). Mutations inherited through the chromosomes can be autosomal dominant or recessive and can also be sex-linked dominant or recessive. Chromosomal inheritance follows normal Mendelian laws, despite the fact that the phenotype of the disease may be masked.

Because of the complex ways in which mitochondrial and nuclear DNA “communicate” and interact, even seemingly simple inheritance is hard to diagnose. A mutation in chromosomal DNA may change a protein that regulates (increases or decreases) the production of another certain protein in the mitochondria or the cytoplasm; this may lead to slight, if any, noticeable symptoms. On the other hand, some devastating mtDNA mutations are easy to diagnose because of their widespread damage to muscular, neural, and/or hepatic tissues (among other high-energy and metabolism-dependent tissues) and because they are present in the mother and all the offspring.

Mitochondrial genome mutations are passed on 100% of the time from mother to all her offspring. So, if a female has a mitochondrial trait, all offspring inherit it. However, if a male has a mitochondrial trait, no offspring inherit it.The number of affected mtDNA molecules inherited by a specific offspring can vary greatly because

It is possible, even in twin births, for one baby to receive more than half mutant mtDNA molecules while the other twin may receive only a tiny fraction of mutant mtDNA molecules with respect to wildtype (depending on how the twins divide from each other and how many mutant mitochondria happen to be on each side of the division). In a few cases, some mitochondria or a mitochondrion from the sperm cell enters the oocyte but paternal mitochondria are actively decomposed.

Genes in the human mitochondrial genome are as follows.

It was originally incorrectly believed that the mitochondrial genome contained only 13 protein-coding genes, all of them encoding proteins of the electron transport chain. However, in 2001, a 14th biologically active protein called humanin was discovered, and was found to be encoded by the mitochondrial gene MT-RNR2 which also encodes part of the mitochondrial ribosome (made out of RNA):

Unlike the other proteins, humanin does not remain in the mitochondria, and interacts with the rest of the cell and cellular receptors. Humanin can protect brain cells by inhibiting apoptosis. Despite its name, versions of humanin also exist in other animals, such as rattin in rats.

The following genes encode rRNAs:

The following genes encode tRNAs:

In humans, the heavy strand of mtDNA carries 28 genes and the light strand of mtDNA carries only 9 genes.[5] Eight of the 9 genes on the light strand code for mitochondrial tRNA molecules. Human mtDNA consists of 16,569 nucleotide pairs. The entire molecule is regulated by only one regulatory region which contains the origins of replication of both heavy and light strands. The entire human mitochondrial DNA molecule has been mapped[1][2].

The genetic code is, for the most part, universal, with few exceptions: mitochondrial genetics includes some of these. For most organisms the “stop codons” are “UAA”, “UAG”, and “UGA”. In vertebrate mitochondria “AGA” and “AGG” are also stop codons, but not “UGA”, which codes for tryptophan instead. “AUA” codes for isoleucine in most organisms but for methionine in vertebrate mitochondrial mRNA.

There are many other variations among the codes used by other mitochondrial m/tRNA, which happened not to be harmful to their organisms, and which can be used as a tool (along with other mutations among the mtDNA/RNA of different species) to determine relative proximity of common ancestry of related species. (The more related two species are, the more mtDNA/RNA mutations will be the same in their mitochondrial genome).

Using these techniques, it is estimated that the first mitochondria arose around 1.5 billion years ago. A generally accepted hypothesis is that mitochondria originated as an aerobic prokaryote in a symbiotic relationship within an anaerobic eukaryote.

Mitochondrial replication is controlled by nuclear genes and is specifically suited to make as many mitochondria as that particular cell needs at the time.

Mitochondrial transcription in humans is initiated from three promoters, H1, H2, and L (heavy strand 1, heavy strand 2, and light strand promoters). The H2 promoter transcribes almost the entire heavy strand and the L promoter transcribes the entire light strand. The H1 promoter causes the transcription of the two mitochondrial rRNA molecules.[6]

When transcription takes place on the heavy strand a polycistronic transcript is created. The light strand produces either small transcripts, which can be used as primers, or one long transcript. The production of primers occurs by processing of light strand transcripts with the Mitochondrial RNase MRP (Mitochondrial RNA Processing). The requirement of transcription to produce primers links the process of transcription to mtDNA replication. Full length transcripts are cut into functional tRNA, rRNA, and mRNA molecules.[citation needed]

The process of transcription initiation in mitochondria involves three types of proteins: the mitochondrial RNA polymerase (POLRMT), mitochondrial transcription factor A (TFAM), and mitochondrial transcription factors B1 and B2 (TFB1M, TFB2M). POLRMT, TFAM, and TFB1M or TFB2M assemble at the mitochondrial promoters and begin transcription. The actual molecular events that are involved in initiation are unknown, but these factors make up the basal transcription machinery and have been shown to function in vitro.[citation needed]

Mitochondrial translation is still not very well understood. In vitro translations have still not been successful, probably due to the difficulty of isolating sufficient mt mRNA, functional mt rRNA, and possibly because of the complicated changes that the mRNA undergoes before it is translated.[citation needed]

The Mitochondrial DNA Polymerase (Pol gamma, encoded by the POLG gene) is used in the copying of mtDNA during replication. Because the two (heavy and light) strands on the circular mtDNA molecule have different origins of replication, it replicates in a D-loop mode. One strand begins to replicate first, displacing the other strand. This continues until replication reaches the origin of replication on the other strand, at which point the other strand begins replicating in the opposite direction. This results in two new mtDNA molecules. Each mitochondrion has several copies of the mtDNA molecule and the number of mtDNA molecules is a limiting factor in mitochondrial fission. After the mitochondrion has enough mtDNA, membrane area, and membrane proteins, it can undergo fission (very similar to that which bacteria use) to become two mitochondria. Evidence suggests that mitochondria can also undergo fusion and exchange (in a form of crossover) genetic material among each other. Mitochondria sometimes form large matrices in which fusion, fission, and protein exchanges are constantly occurring. mtDNA shared among mitochondria (despite the fact that they can undergo fusion).[citation needed]

Mitochondrial DNA is susceptible to damage from free oxygen radicals from mistakes that occur during the production of ATP through the electron transport chain. These mistakes can be caused by genetic disorders, cancer, and temperature variations. These radicals can damage mtDNA molecules or change them, making it hard for mitochondrial polymerase to replicate them. Both cases can lead to deletions, rearrangements, and other mutations. Recent evidence has suggested that mitochondria have enzymes that proofread mtDNA and fix mutations that may occur due to free radicals. It is believed that a DNA recombinase found in mammalian cells is also involved in a repairing recombination process. Deletions and mutations due to free radicals have been associated with the aging process. It is believed that radicals cause mutations which lead to mutant proteins, which in turn led to more radicals. This process takes many years and is associated with some aging processes involved in oxygen-dependent tissues such as brain, heart, muscle, and kidney. Auto-enhancing processes such as these are possible causes of degenerative diseases including Parkinson’s, Alzheimer’s, and coronary artery disease.[citation needed]

Because mitochondrial growth and fission are mediated by the nuclear DNA, mutations in nuclear DNA can have a wide array of effects on mtDNA replication. Despite the fact that the loci for some of these mutations have been found on human chromosomes, specific genes and proteins involved have not yet been isolated. Mitochondria need a certain protein to undergo fission. If this protein (generated by the nucleus) is not present, the mitochondria grow but they do not divide. This leads to giant, inefficient mitochondria. Mistakes in chromosomal genes or their products can also affect mitochondrial replication more directly by inhibiting mitochondrial polymerase and can even cause mutations in the mtDNA directly and indirectly. Indirect mutations are most often caused by radicals created by defective proteins made from nuclear DNA.[citation needed]

In total, the mitochondrion hosts about 3000 different types of proteins, but only about 13 of them are coded on the mitochondrial DNA. Most of the 3000 types of proteins are involved in a variety of processes other than ATP production, such as porphyrin synthesis. Only about 3% of them code for ATP production proteins. This means most of the genetic information coding for the protein makeup of mitochondria is in chromosomal DNA and is involved in processes other than ATP synthesis. This increases the chances that a mutation that will affect a mitochondrion will occur in chromosomal DNA, which is inherited in a Mendelian pattern. Another result is that a chromosomal mutation will affect a specific tissue due to its specific needs, whether those may be high energy requirements or a need for the catabolism or anabolism of a specific neurotransmitter or nucleic acid. Because several copies of the mitochondrial genome are carried by each mitochondrion (210 in humans), mitochondrial mutations can be inherited maternally by mtDNA mutations which are present in mitochondria inside the oocyte before fertilization, or (as stated above) through mutations in the chromosomes.[citation needed]

Mitochondrial diseases range in severity from asymptomatic to fatal, and are most commonly due to inherited rather than acquired mutations of mitochondrial DNA. A given mitochondrial mutation can cause various diseases depending on the severity of the problem in the mitochondria and the tissue the affected mitochondria are in. Conversely, several different mutations may present themselves as the same disease. This almost patient-specific characterization of mitochondrial diseases (see Personalized medicine) makes them very hard to accurately recognize, diagnose and trace. Some diseases are observable at or even before birth (many causing death) while others do not show themselves until late adulthood (late-onset disorders). This is because the number of mutant versus wildtype mitochondria varies between cells and tissues, and is continuously changing. Because cells have multiple mitochondria, different mitochondria in the same cell can have different variations of the mtDNA. This condition is referred to as heteroplasmy. When a certain tissue reaches a certain ratio of mutant versus wildtype mitochondria, a disease will present itself. The ratio varies from person to person and tissue to tissue (depending on its specific energy, oxygen, and metabolism requirements, and the effects of the specific mutation). Mitochondrial diseases are very numerous and different. Apart from diseases caused by abnormalities in mitochondrial DNA, many diseases are suspected to be associated in part by mitochondrial dysfunctions, such as diabetes mellitus, forms of cancer and cardiovascular disease, lactic acidosis, specific forms of myopathy, osteoporosis, Alzheimer’s disease, Parkinsons’s disease, stroke, male infertility and which are also believed to play a role in the aging process.[citation needed]

Human mtDNA can also be used to help identify individuals.[7] Forensic laboratories occasionally use mtDNA comparison to identify human remains, and especially to identify older unidentified skeletal remains. Although unlike nuclear DNA, mtDNA is not specific to one individual, it can be used in combination with other evidence (anthropological evidence, circumstantial evidence, and the like) to establish identification. mtDNA is also used to exclude possible matches between missing persons and unidentified remains.[8] Many researchers believe that mtDNA is better suited to identification of older skeletal remains than nuclear DNA because the greater number of copies of mtDNA per cell increases the chance of obtaining a useful sample, and because a match with a living relative is possible even if numerous maternal generations separate the two. American outlaw Jesse James’s remains were identified using a comparison between mtDNA extracted from his remains and the mtDNA of the son of the female-line great-granddaughter of his sister.[9] Similarly, the remains of Alexandra Feodorovna (Alix of Hesse), last Empress of Russia, and her children were identified by comparison of their mitochondrial DNA with that of Prince Philip, Duke of Edinburgh, whose maternal grandmother was Alexandra’s sister Victoria of Hesse.[10] Similarly to identify Emperor Nicholas II remains his mitochondrial DNA was compared with that of James Carnegie, 3rd Duke of Fife, whose maternal great-grandmother Alexandra of Denmark (Queen Alexandra) was sister of Nicholas II mother Dagmar of Denmark (Empress Maria Feodorovna).[11]

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Human mitochondrial genetics – Wikipedia

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

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genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

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Human genetics | biology | Britannica.com

Human genetics – Wikipedia

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genes can be the common factor of the qualities of most human-inherited traits. Study of human genetics can be useful as it can answer questions about human nature, understand the diseases and development of effective disease treatment, and understand genetics of human life. This article describes only basic features of human genetics; for the genetics of disorders please see: medical genetics.

Inheritance of traits for humans are based upon Gregor Mendel’s model of inheritance. Mendel deduced that inheritance depends upon discrete units of inheritance, called factors or genes.[1]

Autosomal traits are associated with a single gene on an autosome (non-sex chromosome)they are called “dominant” because a single copyinherited from either parentis enough to cause this trait to appear. This often means that one of the parents must also have the same trait, unless it has arisen due to an unlikely new mutation. Examples of autosomal dominant traits and disorders are Huntington’s disease and achondroplasia.

Autosomal recessive traits is one pattern of inheritance for a trait, disease, or disorder to be passed on through families. For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented. The trait or gene will be located on a non-sex chromosome. Because it takes two copies of a trait to display a trait, many people can unknowingly be carriers of a disease. From an evolutionary perspective, a recessive disease or trait can remain hidden for several generations before displaying the phenotype. Examples of autosomal recessive disorders are albinism, cystic fibrosis.

X-linked genes are found on the sex X chromosome. X-linked genes just like autosomal genes have both dominant and recessive types. Recessive X-linked disorders are rarely seen in females and usually only affect males. This is because males inherit their X chromosome and all X-linked genes will be inherited from the maternal side. Fathers only pass on their Y chromosome to their sons, so no X-linked traits will be inherited from father to son. Men cannot be carriers for recessive X linked traits, as they only have one X chromosome, so any X linked trait inherited from the mother will show up.

Females express X-linked disorders when they are homozygous for the disorder and become carriers when they are heterozygous. X-linked dominant inheritance will show the same phenotype as a heterozygote and homozygote. Just like X-linked inheritance, there will be a lack of male-to-male inheritance, which makes it distinguishable from autosomal traits. One example of an X-linked trait is CoffinLowry syndrome, which is caused by a mutation in ribosomal protein gene. This mutation results in skeletal, craniofacial abnormalities, mental retardation, and short stature.

X chromosomes in females undergo a process known as X inactivation. X inactivation is when one of the two X chromosomes in females is almost completely inactivated. It is important that this process occurs otherwise a woman would produce twice the amount of normal X chromosome proteins. The mechanism for X inactivation will occur during the embryonic stage. For people with disorders like trisomy X, where the genotype has three X chromosomes, X-inactivation will inactivate all X chromosomes until there is only one X chromosome active. Males with Klinefelter syndrome, who have an extra X chromosome, will also undergo X inactivation to have only one completely active X chromosome.

Y-linked inheritance occurs when a gene, trait, or disorder is transferred through the Y chromosome. Since Y chromosomes can only be found in males, Y linked traits are only passed on from father to son. The testis determining factor, which is located on the Y chromosome, determines the maleness of individuals. Besides the maleness inherited in the Y-chromosome there are no other found Y-linked characteristics.

A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family. Square symbols are almost always used to represent males, whilst circles are used for females. Pedigrees are used to help detect many different genetic diseases. A pedigree can also be used to help determine the chances for a parent to produce an offspring with a specific trait.

Four different traits can be identified by pedigree chart analysis: autosomal dominant, autosomal recessive, x-linked, or y-linked. Partial penetrance can be shown and calculated from pedigrees. Penetrance is the percentage expressed frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait.

Inbreeding, or mating between closely related organisms, can clearly be seen on pedigree charts. Pedigree charts of royal families often have a high degree of inbreeding, because it was customary and preferable for royalty to marry another member of royalty. Genetic counselors commonly use pedigrees to help couples determine if the parents will be able to produce healthy children.

A karyotype is a very useful tool in cytogenetics. A karyotype is picture of all the chromosomes in the metaphase stage arranged according to length and centromere position. A karyotype can also be useful in clinical genetics, due to its ability to diagnose genetic disorders. On a normal karyotype, aneuploidy can be detected by clearly being able to observe any missing or extra chromosomes.[1]

Giemsa banding, g-banding, of the karyotype can be used to detect deletions, insertions, duplications, inversions, and translocations. G-banding will stain the chromosomes with light and dark bands unique to each chromosome. A FISH, fluorescent in situ hybridization, can be used to observe deletions, insertions, and translocations. FISH uses fluorescent probes to bind to specific sequences of the chromosomes that will cause the chromosomes to fluoresce a unique color.[1]

Genomics refers to the field of genetics concerned with structural and functional studies of the genome.[1] A genome is all the DNA contained within an organism or a cell including nuclear and mitochondrial DNA. The human genome is the total collection of genes in a human being contained in the human chromosome, composed of over three billion nucleotides.[2] In April 2003, the Human Genome Project was able to sequence all the DNA in the human genome, and to discover that the human genome was composed of around 20,000 protein coding genes.

Medical genetics’ is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics is the application of genetics to medical care. It overlaps human genetics, for example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis, management, and counseling of individuals with genetic disorders would be considered part of medical genetics.

Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance.[3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift. A population can be defined as a group of interbreeding individuals and their offspring. For human genetics the populations will consist only of the human species. The Hardy-Weinberg principle is a widely used principle to determine allelic and genotype frequencies.

In addition to nuclear DNA, humans (like almost all eukaryotes) have mitochondrial DNA. Mitochondria, the “power houses” of a cell, have their own DNA. Mitochondria are inherited from one’s mother, and their DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve). Mitochondrial DNA is only 16kb in length and encodes for 62 genes.

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance. Since humans have many more genes on the X than the Y, there are many more X-linked traits than Y-linked traits.However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes.[4]

To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation. In particular, by way of the process called X-chromosome inactivation (XCI), female mammals transcriptionally silence one of their two Xs in a complex and highly coordinated manner.[4]

GeneticChromosomal

[35]

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Human genetics – Wikipedia

Human Genetics – Springer

Human Genetics presents original and timely articles on all aspects of human genetics. Coverage includes gene structure and organization; gene expression; mutation detection and analysis; linkage analysis and genetic mapping; physical mapping; cytogenetics and genomic imaging; genome structure and organization; disease association studies; molecular diagnostics; genetic epidemiology; evolutionary genetics; developmental genetics; genotype-phenotype relationships; molecular genetics of tumorigenesis; genetics of complex diseases and epistatic interactions; ethical, legal and social issues and bioinformatics.

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Human Genetics – Springer

Human genetics – Wikipedia

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genes can be the common factor of the qualities of most human-inherited traits. Study of human genetics can be useful as it can answer questions about human nature, understand the diseases and development of effective disease treatment, and understand genetics of human life. This article describes only basic features of human genetics; for the genetics of disorders please see: medical genetics.

Inheritance of traits for humans are based upon Gregor Mendel’s model of inheritance. Mendel deduced that inheritance depends upon discrete units of inheritance, called factors or genes.[1]

Autosomal traits are associated with a single gene on an autosome (non-sex chromosome)they are called “dominant” because a single copyinherited from either parentis enough to cause this trait to appear. This often means that one of the parents must also have the same trait, unless it has arisen due to an unlikely new mutation. Examples of autosomal dominant traits and disorders are Huntington’s disease and achondroplasia.

Autosomal recessive traits is one pattern of inheritance for a trait, disease, or disorder to be passed on through families. For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented. The trait or gene will be located on a non-sex chromosome. Because it takes two copies of a trait to display a trait, many people can unknowingly be carriers of a disease. From an evolutionary perspective, a recessive disease or trait can remain hidden for several generations before displaying the phenotype. Examples of autosomal recessive disorders are albinism, cystic fibrosis.

X-linked genes are found on the sex X chromosome. X-linked genes just like autosomal genes have both dominant and recessive types. Recessive X-linked disorders are rarely seen in females and usually only affect males. This is because males inherit their X chromosome and all X-linked genes will be inherited from the maternal side. Fathers only pass on their Y chromosome to their sons, so no X-linked traits will be inherited from father to son. Men cannot be carriers for recessive X linked traits, as they only have one X chromosome, so any X linked trait inherited from the mother will show up.

Females express X-linked disorders when they are homozygous for the disorder and become carriers when they are heterozygous. X-linked dominant inheritance will show the same phenotype as a heterozygote and homozygote. Just like X-linked inheritance, there will be a lack of male-to-male inheritance, which makes it distinguishable from autosomal traits. One example of an X-linked trait is CoffinLowry syndrome, which is caused by a mutation in ribosomal protein gene. This mutation results in skeletal, craniofacial abnormalities, mental retardation, and short stature.

X chromosomes in females undergo a process known as X inactivation. X inactivation is when one of the two X chromosomes in females is almost completely inactivated. It is important that this process occurs otherwise a woman would produce twice the amount of normal X chromosome proteins. The mechanism for X inactivation will occur during the embryonic stage. For people with disorders like trisomy X, where the genotype has three X chromosomes, X-inactivation will inactivate all X chromosomes until there is only one X chromosome active. Males with Klinefelter syndrome, who have an extra X chromosome, will also undergo X inactivation to have only one completely active X chromosome.

Y-linked inheritance occurs when a gene, trait, or disorder is transferred through the Y chromosome. Since Y chromosomes can only be found in males, Y linked traits are only passed on from father to son. The testis determining factor, which is located on the Y chromosome, determines the maleness of individuals. Besides the maleness inherited in the Y-chromosome there are no other found Y-linked characteristics.

A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family. Square symbols are almost always used to represent males, whilst circles are used for females. Pedigrees are used to help detect many different genetic diseases. A pedigree can also be used to help determine the chances for a parent to produce an offspring with a specific trait.

Four different traits can be identified by pedigree chart analysis: autosomal dominant, autosomal recessive, x-linked, or y-linked. Partial penetrance can be shown and calculated from pedigrees. Penetrance is the percentage expressed frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait.

Inbreeding, or mating between closely related organisms, can clearly be seen on pedigree charts. Pedigree charts of royal families often have a high degree of inbreeding, because it was customary and preferable for royalty to marry another member of royalty. Genetic counselors commonly use pedigrees to help couples determine if the parents will be able to produce healthy children.

A karyotype is a very useful tool in cytogenetics. A karyotype is picture of all the chromosomes in the metaphase stage arranged according to length and centromere position. A karyotype can also be useful in clinical genetics, due to its ability to diagnose genetic disorders. On a normal karyotype, aneuploidy can be detected by clearly being able to observe any missing or extra chromosomes.[1]

Giemsa banding, g-banding, of the karyotype can be used to detect deletions, insertions, duplications, inversions, and translocations. G-banding will stain the chromosomes with light and dark bands unique to each chromosome. A FISH, fluorescent in situ hybridization, can be used to observe deletions, insertions, and translocations. FISH uses fluorescent probes to bind to specific sequences of the chromosomes that will cause the chromosomes to fluoresce a unique color.[1]

Genomics refers to the field of genetics concerned with structural and functional studies of the genome.[1] A genome is all the DNA contained within an organism or a cell including nuclear and mitochondrial DNA. The human genome is the total collection of genes in a human being contained in the human chromosome, composed of over three billion nucleotides.[2] In April 2003, the Human Genome Project was able to sequence all the DNA in the human genome, and to discover that the human genome was composed of around 20,000 protein coding genes.

Medical genetics’ is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics is the application of genetics to medical care. It overlaps human genetics, for example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis, management, and counseling of individuals with genetic disorders would be considered part of medical genetics.

Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance.[3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift. A population can be defined as a group of interbreeding individuals and their offspring. For human genetics the populations will consist only of the human species. The Hardy-Weinberg principle is a widely used principle to determine allelic and genotype frequencies.

In addition to nuclear DNA, humans (like almost all eukaryotes) have mitochondrial DNA. Mitochondria, the “power houses” of a cell, have their own DNA. Mitochondria are inherited from one’s mother, and their DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve). Mitochondrial DNA is only 16kb in length and encodes for 62 genes.

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance. Since humans have many more genes on the X than the Y, there are many more X-linked traits than Y-linked traits.However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes.[4]

To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation. In particular, by way of the process called X-chromosome inactivation (XCI), female mammals transcriptionally silence one of their two Xs in a complex and highly coordinated manner.[4]

GeneticChromosomal

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Human genetics – Wikipedia

Human genetics | biology | Britannica.com

Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.

The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.

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genetics: Human genetics

Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the

A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by mental retardation. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.

Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.

A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.

Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. The phenomenon of homosexuality is of uncertain cause and is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turners syndrome.

If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.

During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.

Immunity is the ability of an individual to recognize the self molecules that make up ones own body and to distinguish them from such nonself molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.

There are two major components of the immune system, both originating from the same precursor stem cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it remembers the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.

The thymus component of the immune system centres on the thymus-derived T lymphocytes. In addition to regulating the B cells in producing humoral immunity, the T cells also directly attack cells that display foreign antigens. This process, called cellular immunity, is of great importance in protecting the body against a variety of viruses as well as cancer cells. Cellular immunity is also the chief cause of the rejection of organ transplants. The T lymphocytes provide a complex network consisting of a series of helper cells (which are antigen-specific), amplifier cells, suppressor cells, and cytotoxic (killer) cells, all of which are important in immune regulation.

One of the central problems in understanding the genetics of the immune system has been in explaining the genetic regulation of antibody production. Immunobiologists have demonstrated that the system can produce well over one million specific antibodies, each corresponding to a particular antigen. It would be difficult to envisage that each antibody is encoded by a separate gene; such an arrangement would require a disproportionate share of the entire human genome. Recombinant DNA analysis has illuminated the mechanisms by which a limited number of immunoglobulin genes can encode this vast number of antibodies.

Each antibody molecule consists of several different polypeptide chainsthe light chains (L) and the longer heavy chains (H). The latter determine to which of five different classes (IgM, IgG, IgA, IgD, or IgE) an immunoglobulin belongs. Both the L and H chains are unique among proteins in that they contain constant and variable parts. The constant parts have relatively identical amino acid sequences in any given antibody. The variable parts, on the other hand, have different amino acid sequences in each antibody molecule. It is the variable parts, then, that determine the specificity of the antibody.

Recombinant DNA studies of immunoglobulin genes in mice have revealed that the light-chain genes are encoded in four separate parts in germ-line DNA: a leader segment (L), a variable segment (V), a joining segment (J), and a constant segment (C). These segments are widely separated in the DNA of an embryonic cell, but in a mature B lymphocyte they are found in relative proximity (albeit separated by introns). The mouse has more than 200 light-chain variable region genes, only one of which will be incorporated into the proximal sequence that codes for the antibody production in a given B lymphocyte. Antibody diversity is greatly enhanced by this system, as the V and J segments rearrange and assort randomly in each B-lymphocyte precursor cell. The mechanisms by which this DNA rearrangement takes place are not clear, but transposons are undoubtedly involved. Similar combinatorial processes take place in the genes that code for the heavy chains; furthermore, both the light-chain and heavy-chain genes can undergo somatic mutations to create new antibody-coding sequences. The net effect of these combinatorial and mutational processes enables the coding of millions of specific antibody molecules from a limited number of genes. It should be stressed, however, that each B lymphocyte can produce only one antibody. It is the B lymphocyte population as a whole that produces the tremendous variety of antibodies in humans and other mammals.

Plasma cell tumours (myelomas) have made it possible to study individual antibodies, since these tumours, which are descendants of a single plasma cell, produce one antibody in abundance. Another method of obtaining large amounts of a specific antibody is by fusing a B lymphocyte with a rapidly growing cancer cell. The resultant hybrid cell, known as a hybridoma, multiplies rapidly in culture. Since the antibodies obtained from hybridomas are produced by clones derived from a single lymphocyte, they are called monoclonal antibodies.

As has been stated, cellular immunity is mediated by T lymphocytes that can recognize infected body cells, cancer cells, and the cells of a foreign transplant. The control of cellular immune reactions is provided by a linked group of genes, known as the major histocompatibility complex (MHC). These genes code for the major histocompatibility antigens, which are found on the surface of almost all nucleated somatic cells. The major histocompatibility antigens were first discovered on the leukocytes (white blood cells) and are therefore usually referred to as the HLA (human leukocyte group A) antigens.

The advent of the transplantation of human organs in the 1950s made the question of tissue compatibility between donor and recipient of vital importance, and it was in this context that the HLA antigens and the MHC were elucidated. Investigators found that the MHC resides on the short arm of chromosome 6, on four closely associated sites designated HLA-A, HLA-B, HLA-C, and HLA-D. Each locus is highly polymorphic; i.e., each is represented by a great many alleles within the human gene pool. These alleles, like those of the ABO blood group system, are expressed in codominant fashion. Because of the large number of alleles at each HLA locus, there is an extremely low probability of any two individuals (other than siblings) having identical HLA genotypes. (Since a person inherits one chromosome 6 from each parent, siblings have a 25 percent probability of having received the same paternal and maternal chromosomes 6 and thus of being HLA matched.)

Although HLA antigens are largely responsible for the rejection of organ transplants, it is obvious that the MHC did not evolve to prevent the transfer of organs from one person to another. Indeed, information obtained from the histocompatibility complex in the mouse (which is very similar in its genetic organization to that of the human) suggests that a primary function of the HLA antigens is to regulate the number of specific cytotoxic T killer cells, which have the ability to destroy virus-infected cells and cancer cells.

More is known about the genetics of the blood than about any other human tissue. One reason for this is that blood samples can be easily secured and subjected to biochemical analysis without harm or major discomfort to the person being tested. Perhaps a more cogent reason is that many chemical properties of human blood display relatively simple patterns of inheritance.

Certain chemical substances within the red blood cells (such as the ABO and MN substances noted above) may serve as antigens. When cells that contain specific antigens are introduced into the body of an experimental animal such as a rabbit, the animal responds by producing antibodies in its own blood.

In addition to the ABO and MN systems, geneticists have identified about 14 blood-type gene systems associated with other chromosomal locations. The best known of these is the Rh system. The Rh antigens are of particular importance in human medicine. Curiously, however, their existence was discovered in monkeys. When blood from the rhesus monkey (hence the designation Rh) is injected into rabbits, the rabbits produce so-called Rh antibodies that will agglutinate not only the red blood cells of the monkey but the cells of a large proportion of human beings as well. Some people (Rh-negative individuals), however, lack the Rh antigen; the proportion of such persons varies from one human population to another. Akin to data concerning the ABO system, the evidence for Rh genes indicates that only a single chromosome locus (called r) is involved and is located on chromosome 1. At least 35 Rh alleles are known for the r location; basically the Rh-negative condition is recessive.

A medical problem may arise when a woman who is Rh-negative carries a fetus that is Rh-positive. The first such child may have no difficulty, but later similar pregnancies may produce severely anemic newborn infants. Exposure to the red blood cells of the first Rh-positive fetus appears to immunize the Rh-negative mother, that is, she develops antibodies that may produce permanent (sometimes fatal) brain damage in any subsequent Rh-positive fetus. Damage arises from the scarcity of oxygen reaching the fetal brain because of the severe destruction of red blood cells. Measures are available for avoiding the severe effects of Rh incompatibility by transfusions to the fetus within the uterus; however, genetic counselling before conception is helpful so that the mother can receive Rh immunoglobulin immediately after her first and any subsequent pregnancies involving an Rh-positive fetus. This immunoglobulin effectively destroys the fetal red blood cells before the mothers immune system is stimulated. The mother thus avoids becoming actively immunized against the Rh antigen and will not produce antibodies that could attack the red blood cells of a future Rh-positive fetus.

Human serum, the fluid portion of the blood that remains after clotting, contains various proteins that have been shown to be under genetic control. Study of genetic influences has flourished since the development of precise methods for separating and identifying serum proteins. These move at different rates under the impetus of an electrical field (electrophoresis), as do proteins from many other sources (e.g., muscle or nerve). Since the composition of a protein is specified by the structure of its corresponding gene, biochemical studies based on electrophoresis permit direct study of tissue substances that are only a metabolic step or two away from the genes themselves.

Electrophoretic studies have revealed that at least one-third of the human serum proteins occur in variant forms. Many of the serum proteins are polymorphic, occurring as two or more variants with a frequency of not less than 1 percent each in a population. Patterns of polymorphic serum protein variants have been used to determine whether twins are identical (as in assessing compatibility for organ transplants) or whether two individuals are related (as in resolving paternity suits). Whether the different forms have a selective advantage is not generally known.

Much attention in the genetics of substances in the blood has been centred on serum proteins called haptoglobins, transferrins (which transport iron), and gamma globulins (a number of which are known to immunize against infectious diseases). Haptoglobins appear to relate to two common alleles at a single chromosome locus; the mode of inheritance of the other two seems more complicated, about 18 kinds of transferrins having been described. Like blood-cell antigen genes, serum-protein genes are distributed worldwide in the human population in a way that permits their use in tracing the origin and migration of different groups of people.

Hundreds of variants of hemoglobin have been identified by electrophoresis, but relatively few are frequent enough to be called polymorphisms. Of the polymorphisms, the alleles for sickle-cell and thalassemia hemoglobins produce serious disease in homozygotes, whereas others (hemoglobins C, D, and E) do not. The sickle-cell polymorphism confers a selective advantage on the heterozygote living in a malarial environment; the thalassemia polymorphism provides a similar advantage.

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Human genetics | biology | Britannica.com

Human Genetics – Springer

Human Genetics presents original and timely articles on all aspects of human genetics. Coverage includes gene structure and organization; gene expression; mutation detection and analysis; linkage analysis and genetic mapping; physical mapping; cytogenetics and genomic imaging; genome structure and organization; disease association studies; molecular diagnostics; genetic epidemiology; evolutionary genetics; developmental genetics; genotype-phenotype relationships; molecular genetics of tumorigenesis; genetics of complex diseases and epistatic interactions; ethical, legal and social issues and bioinformatics.

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Human Genetics – Springer

Cryptocurrency Price Forecast: Trust Is Growing, But Prices Are Falling

Trust Is Growing…
Before we get to this week’s cryptocurrency news, analysis, and our cryptocurrency price forecast, I want to share an experience from this past week. I was at home watching the NBA playoffs, trying to ignore the commercials, when a strange advertisement caught my eye.

It followed a tomato from its birth on the vine to its end on the dinner table (where it was served as a bolognese sauce), and a diamond from its dusty beginnings to when it sparkled atop an engagement ring.

The voiceover said: “This is a shipment passed 200 times, transparently tracked from port to port. This is the IBM blockchain.”

Let that sink in—IBM.

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Cryptocurrency Price Forecast: Trust Is Growing, But Prices Are Falling

Cryptocurrency News: Bitcoin ETFs, Andreessen Horowitz, and Contradictions in Crypto

Cryptocurrency News
This was a bloody week for cryptocurrencies. Everything was covered in red, from Ethereum (ETH) on down to the Basic Attention Token (BAT).

Some investors claim it was inevitable. Others say that price manipulation is to blame.

We think the answers are more complicated than either side has to offer, because our research reveals deep contradictions between the price of cryptos and the underlying development of blockchain projects.

For instance, a leading venture capital (VC) firm launched a $300.0-million crypto investment fund, yet liquidity continues to dry up in crypto markets.

Another example is the U.S. Securities and Exchange Commission’s.

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Cryptocurrency News: Bitcoin ETFs, Andreessen Horowitz, and Contradictions in Crypto


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