By: Craig Freudenrich, Ph. Dolly was the first cloned mammal. Wilmut and his colleagues transplanted a nucleus from a mammary gland cell of a Finn Dorsett sheep into the enucleated egg of a Scottish blackface ewe. The nucleus-egg combination was stimulated with electricity to fuse the two and to stimulate cell division.
The new cell divided and was placed in the uterus of a blackface ewe to develop. Dolly was born months later. Dolly was shown to be genetically identical to the Finn Dorsett mammary cells and not to the blackface ewe, which clearly demonstrated that she was a successful clone it took attempts before the experiment was successful. Dolly has since grown and reproduced several offspring of her own through normal sexual means.
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. Dolly was a perfectly normal sheep who became the mother of numerous normal lambs. She lived to six and a half years, when she was eventually put down after a contagious disease spread through her flock, infecting cloned and normally reproduced sheep alike.
Before the decades of experiments that led to Dolly, it was thought that normal animals could be produced only by fertilization of an egg by a sperm. 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 fertilization, 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. 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. 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.
Dolly was the culmination of hundreds of cloning experiments that, for example, showed diploid embryonic and fetal cells could be parents of offspring. But there was no way to easily know all the characteristics of the animal that would result from a cloned embryo or fetus. Researchers could freeze a few of the cells of a cell embryo, while going on to produce clones from the other cells; if a desirable animal was produced, they could thaw the frozen cells and make more copies.
But this was impractical because of low success rates. Dolly demonstrated that adult somatic cells also could be used as parents. Thus, one could know the characteristics of the animal being cloned. By my calculations, Dolly was the single success from tries at somatic cell nuclear transfer. Sometimes the process of cloning by somatic cell nuclear transfer still produces abnormal embryos, most of which die.
Most know of no one even considering the feat. And the cloning of animals remains limited—although it is likely growing. Some agricultural cloning is used in the U. He used adult cells—first in mice, although the technique is now feasible in human cells—to make stem cells that can form a wide range of other cells, essentially turning their cellular clocks back to infancy so they could mature into different adults.
Because they are artificially created and can have a variety of futures, they are called induced pluripotent stem or iPS cells. Previous researchers had derived adult frogs from embryonic frog cells or embryonic frog cells from adults—at which point their development stalled. Dolly died on February 14, , at age six from a lung infection common among animals who are not given access to the outdoors. It probably had nothing to do with her being a cloned animal, says Wilmut, now an emeritus professor at the The Roslin Institute at the University of Edinburgh where he did his initial work.
The sheep, made from breast cells, was famously named after Dolly Parton, the American singer known for her large chest as well as her voice. Rather, it helped humanize a research project that might otherwise have seemed detached from everyday life. He and his colleagues were trying to make clones from fetal cells and used adult ones as experimental controls—not expecting that they would actually generate an embryo of their own.
But interest in that idea has declined with the rise of inexpensive synthetic chemicals. Wilmut says he thinks it would be possible to clone a human—but highly unadvisable. The cloning technique used to create Dolly has been shown not to work in primates. He believes it could be possible using other techniques but said he is vehemently opposed to the idea of cloning a person.
Trounson says he believes there is a large market for cloned livestock embryos. The U.
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