Most dog breeds are the result of selective breeding using artificial selection. It is interesting that particularly well-known breeds of dogs arose in this way. This also serves to show that mutation plays a large role in the diversity of a species.
A team from the American National Human Genome Research Institute, in Maryland, examined DNA samples from 835 dogs from 76 breeds, including 95 animals with short legs.
The scientists found that dogs from all the short-legged breeds had an extra copy of a gene that produces a growth protein called FGF4, which is known to be implicated in dwarfism in humans. The extra gene is a mutant of a type known as a retrogene, which lacks parts of the normal DNA code.
The extra retrogene leads to an overproduction of the FGF4 protein, which appears to alter the times at which bones grow in embryonic development. This, the scientists believe, causes the legs of small dogs to remain short and out of proportion to their bodies. The findings are published in the journal Science. As the same gene is shared between all the short-legged breeds of dog studied, the mutation is likely to have emerged early in the evolution of dogs.
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