Several geneticists at Stanford University have discovered a variant of the gene responsible for the black hair of wolves, which at some point have been crossed with house dogs. To do this, they have analyzed the wolves of Yellowstone National Park, among others.
The loss of three letters of the genetic code of the K locus gene is responsible for several dog breeds of hair or black skin. This same mutation has been observed in 102 wolves of the 104 wolves analyzed in Yellowstone National Park. Therefore, they do not doubt that this genetic variety comes from crossing with domestic dogs.