Centuries of selective breeding have given rise to a staggering variety of dog breeds, each with its own traits and behaviors. But shallow gene pools have also put some breeds at higher risk for disease. Dr. Elaine Ostrander runs the Dog Genome Project at the National Human Genome Research Institute. Her team includes Dr. Heidi Parker. Together, they are digging for clues to understand how genes code for dogs' diversity and disease. Clues that might also inform the health of their two-legged caregivers.