Cornell researchers help identify gene that plays key role in size of dogs - and probably in humans

10-Apr-2007

An international team of scientists, including researchers from Cornell University, have found a mutation in a single gene that plays a key role in determining body-size differences within and among dog breeds and probably is important in determining the size of humans as well.

The research, published in Science, "is one of the first demonstrations that if you look at different dog breeds that share the same trait (such as large or small size or short legs or scrunched-up faces) due to human-directed selection, you will find genes that are likely to affect the same traits in humans," said co-author Carlos Bustamante, assistant professor of biological statistics and computational biology at Cornell.

The researchers began by comparing the DNA of individuals within a single dog breed that shows great variation in skeletal size - Portuguese water dogs - and identifying regions of the genome that differ between small and large individuals. One of these regions included a gene that codes for a protein hormone called insulin-like growth factor 1 (IGF1), which is known to play an important role in growth, body size and longevity in mice and in body size in humans. The researchers then analyzed this region in hundreds of dogs from 14 small dog breeds, such as Chihuahuas, toy fox terriers and Pomeranians, and nine large dog breeds, including Irish wolfhounds, Saint Bernards and Great Danes.

Surprisingly, almost all of the dogs from the small breed shared a stretch of DNA that was identical to that found in small Portuguese water dogs, but different from that found in large breeds, large Portuguese water dogs, wolves and other wild members of the dog family, such as jackals. Researchers suspect a single mutation early in the domestication history of dogs created a "small dog" version (or allele) of IGF1. This mutation became fixed in small dog breeds through human breeding of the dogs. The results suggest that IGF1plays a similar role in differentiating small from large dogs within breeds, small from large breeds within dogs, and likely size differences among species.

"It is staggering to think that so many of the small dog breeds came about through selection on the same mutation in the same gene. These results suggest that while there are invariably differences among breeds (even in genes for size), IGF1 has played an important role in the evolution of many small breeds by being a gene that consistently affects body size," said Bustamante. "The research points to the utility of the domestic dog model system to identify genes that have a large effect."

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