Stanford University researchers have identified the gene  that makes dogs' fur black, and may also shed light on differences in people's body size and ability to cope with stress! The work narrowed the genome region to a gene that makes a beta-defensin protein – one version of this beta-defensin gene produces yellow pups, and another produces black. In fact, all dog coat colors are modifications of black and yellow! A Dalmatian, for example, may appear spotted but, based on genetics, it's considered black.
This project started a couple years ago with Boxers and Great Danes of different colors. Once the genome that differed between them was identified, scientists moved on to 36 other dog breeds, gathering hundreds of cheek swab samples. A human can have between 40 and 50 different defensin genes; dogs can have up to 46. This one is part of the melanocortin pathway – shared by canines and humans – that determines skin and hair color along with weight and stress adaptation.