The findings will appear in an upcoming issue of the Proceedings of the National Academy of Sciences and are available online.

“We’re offering an explanation for a lot of different components of evolution, one that goes against the central dogma that currently explains how certain aspects of evolution take place,” said Dr. Harold “Skip” Garner, professor of biochemistry and internal medicine at UT Southwestern and one of the authors of the study, which involved only small, non-invasive blood draws from dogs by licensed veterinarians.

In the same genetic region from wild coyotes and wolves, the researchers also found variations in repeat lengths, but these animals do not have nearly the wide range of variation in repeat length that domestic dogs do. Consequently, they also don’t have the range in physical variation in muzzle length.

Mutations in tandem repeat sequences occur much more frequently than single point mutations – up to 100,000 times as often – and are much more likely to result in significant morphological changes, or changes in physical appearance, in an organism, said Dr. Fondon, an evolutionary biologist.

“I was struck by the prevalence of very highly mutable tandem repeats in the coding regions of genes responsible for development,” he said. “That’s when it occurred to me that this may be an important mechanism whereby our genomes are able to create lots of useful variations in genes that are important for our development, our shape and structure, and our overall appearance.

“Many of the shape difference that we see in evolution are not suddenly adding a wing or a leg. They are distortions, the stretching or squishing of a body part. Mutations in these repeat sequences are responsible for such incremental, quantitative changes.”

The researchers say the same processes may play an important role in the subtle variations between people. In addition, in humans and in other animals, tandem repeat sequences are found in genes responsible for neurological development, an area where humans have evolved rapidly.

“We have demonstrated that the tandem repeat sequences found in many genes are probably responsible for rapidly evolving physical traits that affect a species’ ability to survive,” Dr. Garner said. “Dogs have been rapidly bred to have many different shapes and traits that are pleasing to humans, enabling them to survive. Humans rapidly evolved big brains, which helped them survive as well.”

The next step in the research is to determine whether tandem repeat mutations behave in a similar manner in other animals, such as mice, and whether such genetic information can be used to predict what an animal will look like.

The research was funded by the National Cancer Institute and the M.R. and Evelyn Hudson Foundation.  Text for this article comes from a UT press release.