These playful companions—a chihuahua–toy poodle mix and a Scottish deerhound—are both representatives of the species Canis familiaris. How a single species can exhibit such immense variation in size and other attributes has become a compelling question for mammalian geneticists. Recent sequencing of the dog genome has provided new insights into what a dog breed really is and has contributed to new techniques for mapping genes controlling body shape and size. Photograph courtesy of Tyrone Spady and Elaine A. Ostrander.
Check out Elaine A Ostrander’s wonderful article, “Genetics and the Shape of Dogs: Studying the new sequence of the canine genome shows how tiny genetic changes can create enormous variation within a single species”