Dolly was an important milestone, inspiring scientists to continue improving cloning technology as well as to pursue new concepts in stem cell research. The endgame was never meant to be armies of genetically identical livestock: Rather, researchers continue to refine the techniques and combine them with other methods to turbocharge traditional animal breeding methods as well as gain insights into aging and disease. <\/p>\n
Before the decades of experiments that led to Dolly, it was thought that normal animals could be produced only by fertilisation of an egg by a sperm. Thats how things naturally work. These germ cells are the only ones in the body that have their genetic material all jumbled up and in half the quantity of every other kind of cell. That way when these so-called haploid cells come together at fertilisation, they produce one cell with the full complement of DNA. Joined together, the cell is termed diploid, for twice, or double. Two halves make a whole. <\/p>\n
From that moment forward, nearly all cells in that body have the same genetic makeup. When the one-cell embryo duplicates its genetic material, both cells of the now two-cell embryo are genetically identical. When they, in turn, duplicate their genetic material, each cell at the four-cell stage is genetically identical. This pattern goes on so that each of the trillions of cells in an adult is genetically exactly the same whether its in a lung or a bone or the blood. <\/p>\n<\/p>\n
In somatic cell nuclear transfer, all the DNA comes from a single adult cell. Belkorin, CC BY-SA <\/p>\n
In contrast, Dolly was produced by whats called somatic cell nuclear transfer. In this process, researchers remove the genetic material from an egg and replace it with the nucleus of some other body cell. The resulting egg becomes a factory to produce an embryo that develops into an offspring. No sperm is in the picture; instead of half the genetic material coming from a sperm and half from an egg, it all comes from a single cell. Its diploid from the start. <\/p>\n
Dolly demonstrated that adult somatic cells also could be used as parents. Thus, one could know the characteristics of the animal being cloned. <\/p>\n
By my calculations, Dolly was the single success from 277 tries at somatic cell nuclear transfer. Sometimes the process of cloning by somatic cell nuclear transfer still produces abnormal embryos, most of which die. But the process has greatly improved so success rates now are more like 10 percent; its highly variable, though, depending on the cell type used and the species. <\/p>\n
More than 10 different cell types have been used successfully as parents for cloning. These days most cloning is done using cells obtained by biopsying skin. <\/p>\n
Environment plays a huge role for some characteristics. Food availability can influence weight. Diseases can stunt growth. These kinds of lifestyle, nutrition or disease effects can influence which genes are turned on or off in an individual; these are called epigenetic effects. Even though all the genetic material may be the same in two identical clones, they might not be expressing all the same genes. <\/p>\n<\/p>\n
Cloning a winner doesnt guarantee success for the next generation. AP Photo\/Darron Cummings <\/p>\n
Consider the practice of cloning winning racehorses. Clones of winners sometimes also will be winners but most of the time theyre not. This is because winners are outliers; they need to have the right genetics, but also the right epigenetics and the right environment to reach that winning potential. For example, one can never exactly duplicate the uterine conditions a winning racehorse experienced when it was a developing fetus. Thus, cloning champions usually leads to disappointment. On the other hand, cloning a stallion that sires a high proportion of race-winning horses will result very reliably in a clone that similarly sires winners. This is a genetic rather than a phenotypic situation. <\/p>\n
Even though the genetics are reliable, there are aspects of the cloning procedure that mean the epigenetics and environment are suboptimal. For example, sperm have elegant ways of activating the eggs they fertilise, which will die unless activated properly; with cloning, activation usually is accomplished by a strong electric shock. Many of the steps of cloning and subsequent embryonic development are done in test tubes in incubators. These conditions are not perfect substitutes for the female reproductive tract where fertilisation and early embryonic development normally occur. <\/p>\n
Sometimes abnormal fetuses develop to term, resulting in abnormalities at birth. The most striking abnormal phenotype of some clones is termed large offspring syndrome, in which calves or lambs are 30 or 40 percent larger than normal, resulting in difficult birth. The problems stem from an abnormal placenta. At birth, these clones are genetically normal, but are overly large, and tend to be hyperinsulinemic and hypoglycemic. (The conditions normalise over time once the offspring is no longer influenced by the abnormal placenta.) <\/p>\n
Recent improvements in cloning procedures have greatly reduced these abnormalities, which also occur with natural reproduction, but at a much lower incidence. <\/p>\n<\/p>\n
Removing genetic material from the nucleus of a cell. AP Photo\/Thomas Terry <\/p>\n
But the cloning research landscape is changing fast. The driving force for producing Dolly was not to produce genetically identical animals. Rather researchers want to combine cloning techniques with other methods in order to efficiently change animals genetically much quicker than traditional animal breeding methods that take decades to make changes in populations of species such as cattle. <\/p>\n
One recent example is introducing the polled (no horns) gene into dairy cattle, thus eliminating the need for the painful process of dehorning. An even more striking application has been to produce a strain of pigs that is incapable of being infected by the very contagious and debilitating PRRS virus. Researchers have even made cattle that cannot develop Mad Cow Disease. For each of these procedures, somatic cell nuclear transplantation is an essential part of the process. <\/p>\n
To date, the most valuable contribution of these somatic cell nuclear transplantation experiments has been the scientific information and insights gained. Theyve enhanced our understanding of normal and abnormal embryonic development, including aspects of aging, and more. This information is already helping reduce birth defects, improve methods of circumventing infertility, develop tools to fight certain cancers and even decrease some of the negative consequences of aging in livestock and even in people. Two decades since Dolly, important applications are still evolving. <\/p>\n
This article was originally published on The Conversation. Read the original article. <\/p>\n
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20 years after Dolly: Everything you always wanted to know about ... - Bizcommunity.com<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" Dolly was an important milestone, inspiring scientists to continue improving cloning technology as well as to pursue new concepts in stem cell research. The endgame was never meant to be armies of genetically identical livestock: Rather, researchers continue to refine the techniques and combine them with other methods to turbocharge traditional animal breeding methods as well as gain insights into aging and disease Continue reading