Washington, July 17 (IANS) Scientists have stumbled on an evolutionary discovery that seems to explain the short, curved legs so characteristic of dachshunds, corgis, basset hounds and other dog breeds.
The discovery provides new clues about how physical differences may arise within species and suggests new approaches to understanding a form of human dwarfism.

Researchers led by National Human Genome Research Institute (NHGRI)’s Elaine Ostrander examined DNA samples from 835 dogs, including 95 with short legs.

Their survey of more than 40,000 markers of DNA variation uncovered a genetic signature exclusive to short-legged breeds.

Through follow-up DNA sequencing and computational analyses, they determined the dogs’ disproportionately short limbs can be traced to one mutational event in the canine genome — a DNA insertion — that occurred early in the evolution of domestic dogs.

“Every species, including canine and human, carries an amazing record of evolution scripted in its genome that can teach us about the mechanisms at work in biology, as well as about human health and disease,” said NHGRI scientific director Eric Green.

“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.