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.
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.
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.
Genomics refers to the field of genetics concerned with structural and functional studies of the genome. 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. 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. 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.
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.
- Cryptocurrency News: This Week on Bitfinex, Tether, Coinbase, & More - May 25th, 2019
- Ripple Price Forecast: XRP vs SWIFT, SEC Updates, and More - May 25th, 2019
- Cryptocurrency News: Bitcoin ETFs, Andreessen Horowitz, and Contradictions in Crypto - May 25th, 2019
- Cryptocurrency News: Looking Past the Bithumb Crypto Hack - May 25th, 2019
- Cryptocurrency News: XRP Validators, Malta, and Practical Tokens - May 25th, 2019
- Cryptocurrency News: Bitcoin ETF Rejection, AMD Microchip Sales, and Hedge Funds - May 25th, 2019
- Cryptocurrency News: What You Need to Know This Week - May 25th, 2019
- Bitcoin Rise: Is the Recent Bitcoin Price Surge a Sign of Things to Come or Another Misdirection? - May 25th, 2019
- Cryptocurrency News: Vitalik Buterin Doesn’t Care About Bitcoin ETFs - May 25th, 2019
- Cryptocurrency News: New Exchanges Could Boost Crypto Liquidity - May 25th, 2019
- Human genetics - Wikipedia - May 5th, 2019
- Human genetics - Wikipedia - May 5th, 2019
- Human Genetics - medschool.ucla.edu - May 5th, 2019
- Department of Human Genetics | The University of Chicago - May 5th, 2019
- Human genetics - Wikipedia - May 2nd, 2019
- Human genetics | biology | Britannica.com - May 2nd, 2019
- Department of Human Genetics | The University of Chicago - May 2nd, 2019
- What is Bitcoin Cash? - finance.yahoo.com - April 29th, 2019
- Bitcoin Cash (BCH) Price, historic Charts and detailed Metrics - April 29th, 2019
- Bitcoin Cash (BCH) price, charts, market cap, and other ... - April 29th, 2019
- Bitcoin Soars As Ethereum, Ripple's XRP, Bitcoin Cash, And ... - April 29th, 2019
- Bitcoin Cash - finance.yahoo.com - April 29th, 2019
- What is Bitcoin Cash? - Coin Rivet - April 29th, 2019
- Moon Cash | Free bitcoin cash faucet - April 29th, 2019
- Cash App - Bitcoin - April 29th, 2019
- Bitcoin Cash (BCH) price, chart, and fundamentals info ... - April 29th, 2019
- Bitcoin Cash - Wikipedia - April 29th, 2019
- Bitcoincash price | index, chart and news | WorldCoinIndex - April 29th, 2019
- Bitcoin Cash (BCH) Price, View BCH Live Value & Buy Bitcoin ... - April 29th, 2019
- Ripple Price Forecast: XRP vs SWIFT, SEC Updates, and More - April 21st, 2019
- Cryptocurrency News: Looking Past the Bithumb Crypto Hack - April 21st, 2019
- Cryptocurrency News: This Week on Bitfinex, Tether, Coinbase, & More - April 21st, 2019
- Cryptocurrency News: XRP Validators, Malta, and Practical Tokens - April 21st, 2019
- Cryptocurrency News: Bitcoin ETFs, Andreessen Horowitz, and Contradictions in Crypto - April 21st, 2019
- Cryptocurrency News: New Exchanges Could Boost Crypto Liquidity - April 21st, 2019
- Cryptocurrency News: Bitcoin ETF Rejection, AMD Microchip Sales, and Hedge Funds - April 21st, 2019
- Cryptocurrency News: What You Need to Know This Week - April 21st, 2019
- Bitcoin Rise: Is the Recent Bitcoin Price Surge a Sign of Things to Come or Another Misdirection? - April 21st, 2019
- Cryptocurrency News: Vitalik Buterin Doesn’t Care About Bitcoin ETFs - April 21st, 2019
- Human genetics | biology | Britannica.com - April 20th, 2019
- Human Genetics - Springer - April 20th, 2019
- Scientists Say New Quantum Material Could “‘Download’ Your Brain” - April 12th, 2019
- Scientists Find a New Way to Kickstart Stable Fusion Reactions - April 12th, 2019
- The Israeli Moon Lander Is About to Touch Down - April 12th, 2019
- Some People Are Exceptionally Good at Predicting the Future - April 12th, 2019
- MIT Prof: If We Live in a Simulation, Are We Players or NPCs? - April 12th, 2019
- Here’s How Big the M87 Black Hole Is Compared to the Earth - April 12th, 2019
- Amazon Workers Listen to Your Alexa Conversations, Then Mock Them - April 12th, 2019
- We Wouldn’t Have the First Black Hole Image Without Katie Bouman - April 12th, 2019
- NASA Is Funding the Development of 18 Bizarre New Projects - April 12th, 2019
- Report: Tesla Doc Is Playing Down Injuries to Block Workers’ Comp - April 12th, 2019
- Infertile Couple Gives Birth to “Three-Parent Baby” - April 12th, 2019
- Space Station Mice Learned to Propel Themselves in Zero Gravity - April 12th, 2019
- NASA: Genetic Changes Caused by Space Travel Are Temporary - April 12th, 2019
- Israel’s Lunar Lander Just Crashed Into the Moon - April 12th, 2019
- The First Black Hole Photo Is Even More Amazing When You Zoom Out - April 12th, 2019
- Family Caught Selling Diseased Body Parts to Medical Centers - April 12th, 2019
- SpaceX Milestone: Company Lands Three Falcon Heavy Boosters - April 12th, 2019
- People Are Horrified When They Have to Torture a Virtual Person - April 12th, 2019
- Fecal Transplants Reduce Symptoms of Autism Long Term - April 12th, 2019
- Astronomy - Wikipedia - April 11th, 2019
- Astronomy Picture of the Day - April 11th, 2019
- astronomy | Definition & Facts | Britannica.com - April 11th, 2019
- Astronomy | Definition of Astronomy by Merriam-Webster - April 11th, 2019
- Elon Musk: $47,000 Model Y SUV “Will Ride Like a Sports Car” - March 16th, 2019
- Just 19 Percent of Americans Trust Self-Driving Cars With Kids - March 16th, 2019
- Special Announcement: Futurism Media and Singularity University - March 16th, 2019
- Samsung Is Working on Phone With “Invisible” Camera Behind Screen - March 16th, 2019
- This Guy Spent a Whole Week In a VR Headset - March 16th, 2019
- How Can We Build Cities to Accommodate 6.5 Billion People? - March 16th, 2019
- Elon Musk: 2019 Will Be “the Year of the Solar Roof” - March 16th, 2019
- Presidential Hopeful Beto O’Rourke Belonged to Infamous Hacker Group - March 16th, 2019
- Slack Just Removed a Bunch of Hate Groups - March 16th, 2019
- Here’s How Hackers Stole $15 Million From Mexican Banks - March 16th, 2019
- States Are Approving Cannabis to Fight Opioid Addiction - March 16th, 2019
- This Tech Could Secure Medical Implants Against Hackers - March 16th, 2019
- NASA: Space Travel Is Causing Astronauts’ Herpes to Flare Up - March 16th, 2019
- New Robot Hand Works Like a Venus Flytrap to Grip Objects - March 16th, 2019
- The Pentagon Wants an Orbital Space Weapon to Blast Enemy Missiles - March 16th, 2019
- Computer Fraud Laws are Flawed, this Lawyer is Fighting Against Them - March 16th, 2019