The B Locus in Dogs

This webpage is part of a series on Dog Coat Color Genetics and was last updated on October 10, 2010 by Sheila Schmutz


The gene at the B locus in dogs is Tyrosinase Related Protein 1 (TYRP1). This same gene causes brown in several other species, such as mice, cattle and cats. Brown is a type of eumelanin pigment.

The two dogs at the left are representatives of the two possible color phases of the Large Munsterlander. Most Large Munsterlanders are black and white but occasionally a brown and white one is born. All Small Munsterlanders are brown and white.

The reason that the German Longhair, who is E/E, is always brown or brown and white and the Large Munsterlander, who is also E/E is usually black and white, is due to TYRP1. The black allele B is dominant to the brown alleles (bS,bd, bc). There are actually 3 common mutations (bS,bd, bc) and perhaps additional rare ones that occur in this gene which result in brown instead of black eumelanin production. The alleles were named based on the type of mutation involved. Most of the DNA testing companies simply report all the alleles as b.

  • Schmutz, S. M., T. G. Berryere, and A. D. Goldfinch. 2002. TYRP1 and MC1r genotypes and their effects on coat color in dogs. Mammalian Genome 13:380-387.
  • The nose leather, pads, and eye rims are also affected by this gene. They are black if a B allele is present but brown if not. Hence all brown dogs have a brown nose and all black dogs have a black nose but red, fawn, sable, white, etc. dogs could have either black or brown noses.

    In dogs which are yellow to red (e/e at MC1r), TYRP1 mutations affect the nose and pad coloration, changing it from black to brown. Yellow lab puppies can have black or brown noses, but Vizslas always have brown or flesh colored noses.

    All dogs which have brown coat color have at least one E or Em allele so that eumelanin is produced. The German Longhair, above, is homozygous for one of the common mutations. Her genotype is bdbd. The brown Large Munsterlander, above, is homozygous for the other with a genotype of bsbs. The Newfoundland, at the right, is homozygous for the rarer brown mutation. His genotype is E/E, bc/bc. Dogs which have any of these mutations on both chromosomes would also be brown, i.e. bs/bd

    .

    Although Sabastian, the Newfoundland appears to be a darker shade of brown than the other two dogs, we do not think that it is due to which b alleles he has. We have studied a litter of Cheasapeake Bay Retrievers (whelped by Macy below) who had different shades of brown, but all had the same genotype of b alleles.

    Smaller breeds such as the American Cocker Spaniel can also be brown.

    In some breeds, such as Doberman Pinschers and Australian Shepherd the brown dogs are called red. See the chart below for the various terms used for brown by various breeds. The miniature Aussie at the right, is brown-and-tan.

    The typical Weimaraner is also brown, but a dilute brown. See more about dilute due to MLPH mutations on another page.

  • W.M. Gerding, S. Schreiber, G. Dekomien & J.T. Epplen 2010. Tracing the origin of 'blue Weimaraner' dogs by molecular genetics. Journal of Animal Breeding and Genetics.

  • Breeds in which brown dogs of with TYRP1 DNA changes have been detected

    The list of alleles may not be complete because relatively few dogs have been tested for some breeds