Researchers find gene that determines dog size

Researchers have finally solved one of the great canine mysteries: Why are small dogs small? As it turns out, small dogs all bear a tiny piece of regulatory DNA that shuts off the gene that produces a powerful growth factor. The gene regulator was probably inherited from a miniature wolf about 15,000 years ago a -- though it has since disappeared from the wolf population -- and has spread rapidly throughout the dog world by human intervention. "All dogs under 20 pounds have this -- all of them," said biologist K. Gordon Lark of the University of Utah, one of the authors of the paper published today in the journal Science. "That's extraordinary." The discovery helps explain the great diversity in size among dog breeds, the greatest diversity among any mammalian species. It also may have implications for humans. "By learning how genes control body size in dogs, we are apt to learn something about how skeletal size is genetically programmed in humans," said geneticist Elaine Ostrander of the National Human Genome Research Institute, who led the study. The gene in question, IGF-1, is the blueprint for a protein called insulinlike growth factor, which not only plays a role in human growth but also is implicated in cancer and certain skeletal diseases.