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.
Consider the practice of cloning winning racehorses. 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. 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 fertilize , 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 fertilization and early embryonic development normally occur. Sometimes abnormal fetuses develop to term , resulting in abnormalities at birth. An inkling that this approach might work, says Wilmut, came from the success his team experienced in producing live lambs from embryonic clones.
It was a high-risk project, and in the beginning Wilmut proceeded with great secrecy, limiting his core team to four scientists. His caution proved to be justified; the scientists failed far more often than they succeeded. Out of tries, the researchers eventually produced only 29 embryos that survived longer than six days. Of these, all died before birth except Dolly, whose historic entry into the world was witnessed by a handful of researchers and a veterinarian.
Dolly the sheep was euthanized in , after developing lung disease—and raising questions about whether being cloned from a 6-year-old ewe made her age more quickly.
Dolly with her triplets Lucy, Darcy and Cotton. Dolly spent her whole life living in a flock of sheep at the Roslin Institute. Dolly had six lambs with a Welsh Mountain sheep named David. Their first lamb, Bonny, was born in the spring of Twins, Sally and Rosie, followed the next year and triplets, called Lucy, Darcy and Cotton, the year after that. Dolly having an ultrasound scan during one of her pregnancies. Dolly the Sheep with her first born lamb, called Bonnie.
Dolly the sheep in a field. In the autumn of , Dolly was seen to be walking stiffly. X-rays confirmed that Dolly had arthritis. It fuelled the suspicion that cloned animals were destined to age prematurely. The cause of the arthritis was never established but daily anti-inflammatory treatment resolved the clinical signs within a few months. Although her arthritis was a concern for the animal carers at Roslin, a much more serious problem was feared. 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. In China a company called Boyalife Group has plans to produce at least , cloned beef cattle—a fraction of the total number of animals slaughtered each year in that country, a company spokesperson wrote via e-mail. Theoretically, cloning could also be used to bring back endangered species.
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