B-locus (alleles: bd, bc, bs) (brown, chocolate, liver(nose))

Two alleles for the TYRP1-gene exist in dogs: the dominant full colour (B) and the recessive brown (b) which is also known in some breeds as liver, chocolate, sedge, and less frequently red. Two copies of the b-allele are needed to vary black pigment to brown. For red or yellow dogs, the brown allele does not dilute the hair colour, but will change the colour of nose and foot pads from black to brown if two brown alleles (b/b) are present. Please note: There are three primary "b" mutations that are responsible for nearly every liver or chocolate dog. A notable exception is the French Bulldog where in addition to these three mutations, there is a fourth cause of chocolate that has yet to be identified.