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The Cheetah (Way to extinction)


Plants and animals extinction has many causes. Human often cause changes in the  environment  that reduce or eliminate food , living space , and breeding grounds thus modifying or destroying habitats. In the case of the cheetah which the Convention of International Trade in Endangered Species has listed as threatened by extinction other factors may be more important. Estimates of the cheetah population vary from 1000 to 25000 animals. Recent studies have shown that a population bottleneck has limited the population. At some time in the cheetah’s recent evolutionary history an infections disease or a natural catastrophe must have reduced its population. This in turn caused a reduction in the variety of alleles in its gene pool.


To test the hypothesis that a population bottleneck  had reduced the genetic variations in the cheetah and was an important factor in the decline in the cheetah population, scientists used their knowledge of transplant and skin graft rejections in humans. Frequently an organ transplant or a skin graft is rejected because the donated organ or skin is recognized as foreign by the immune system of the recipient the greater the possibility of rejection. In genetically similar individuals the chances of rejection are greatly reduced.
The researchers exchanged skin graft between six pairs of unrelated cheetahs. They also grafted patches from one part to another of each cheetah. As a second control, the researchers grafted skin patches from another species the domestic cat, onto each cheetah. There was no rejection of the graft between unrelated cheetahs or between parts of the same cheetah. The graft from the domestic cat however shows acute rejection.
The rejection of the grafts from the domestic cat indicated that the cheetah’s immune system was responsive to genetically different transplanted tissues. Therefore if there were a normal  variation of alleles in the gene pool, one would expect grafts between unrelated cheetahs to be rejected after 7 to 13 days. The non rejection of these grafts supported the hypothesis that the population bottleneck reduced the allelic variation in the gene pool of the cheetah .
The cheetah population is an example of a genetically uniform species that could be wiped out by a deadly infectious disease. Should such a disaster happen, evolution of the cheetah species would stop, and it would become one of the many animals species that are known only through books and museums.
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