Great Danes stretch more than a meter from paw to shoulder and can easily weigh more than 90 kilograms. A Chihuahua fits snugly inside a purse. Domestic dog breeds are more varied in body size and shape -- not to mention coat color and fur length -- than any other land-based mammal. Yet, according to a new study, a mere two to six regions in doggy DNA account for most of this diversity.

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