It seems that the gene that causes the white in the coat is likely the same for both, but the Biewer breeders have more closely line bred to "control" the patterning to conform to a "standard". Additionally, breeders have taken the dogs in two different directions for a variety of reasons - to gain acceptance in one club or another or the belief that their breeding methods are in the best interest of their goals. Have I got it summed up?
