With more than 400 genetically distinct breeds worldwide, the domestic dog is the most diverse land mammal. After 14,000 years of artificial selection for traits such as size, shape and color, the 40-chromosome canine genome holds the secrets to man's best friend's most defining features. And as scientists begin to understand what gives dogs their spots, they're learning a little something about humans, too.

View a slideshow of dogs, their genes and their human connections