'This work provides surprising evidence of a new way in which genome evolution may serve to generate diversity within a species,' Green said.

Specifically, researchers found that in contrast to others, all short-legged dog breeds have an extra copy of the gene that codes for a growth-promoting protein called fibroblast growth factor 4 (FGF4).

Although functional, the extra gene lacks certain parts of the DNA code, called introns, found in normal genes.

These characteristics led researchers to conclude that the extra gene is a so-called retrogene that was inserted into the dog genome some time after the ancestor of modern dog breeds diverged from wolves, said an NHGRI release.

'Our findings may prove valuable to scientists studying other aspects of human growth and development. The work also underscores the value of canine studies for uncovering new biological mechanisms that are likely relevant to human disease,' said Ostrander.

These findings have been published in the advance online edition of Science.