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An international team led by researchers from the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH), has identified a genetic variant that is a major contributor to small size in dogs. The findings appear in the April 6, 2007 issue of the journal Science. “The identification and characterization of a key genetic variant that accounts for differences in dog size is particularly exciting because the underlying gene is present in all dogs and other diverse species, including humans,” said Eric Green, M.D., Ph.D., scientific director of the NHGRI Division of Intramural Research. “Discoveries like this illustrate the exciting promise of genomics research for understanding the inheritance of a wide range of traits, including those that have an impact on health and disease.” In their study, researchers explored the genetic basis for size variation among dogs by comparing the DNA of various small dog breeds, including Chihuahuas, Toy Fox Terriers and Pomeranians, to an array of larger dog breeds, including Irish Wolfhounds, Saint Bernards and Great Danes. Their investigation found that variation in one gene — IGF-1, which codes for a protein hormone called insulin-like growth factor 1, is very strongly associated with small stature across all dog breeds branch of the canine family tree that includes domestic dogs diverged from that of the gray wolf more than 15,000 years ago. Due to selective breeding by humans throughout history, dogs today exhibit an extremely wide range of body types and behaviors. In fact, dogs exhibit the greatest diversity in body size of any mammalian species.
