Coat Colour B-Locus (Brown, 4 variants) – Dog

Coat colour in dogs is controlled by a wide range of different genes working together. These genes are often referred to as ‘loci’. The Brown, or B-Locus, corresponds to the gene ‘tyrosinase-related protein 1’ (TYRP1), which controls the production of eumelanin (black pigment). Several different mutations on the B-Locus are known to result in the lightening of this pigment to brown. The wild-type (normal, un-mutated) allele of the B-locus is designated as B, and is dominant. The recessive mutated allele, which causes the change to brown, is designated as b. This means that only dogs with the genotype b/b will develop a brown coat colour; B/b and B/B dogs will not be affected.

The variants of the B-locus mutation analysed by CombiBreed are bc, bs and bd (all of which occur in a wide variety of breeds), as well as be (specific to the Lancashire Heeler) and bh (specific to the Siberian Husky). These mutations each cause the same basic features, and a dog with a combination of any two of them should be considered as having genotype b/b.

Affected dogs that would otherwise have black hair develop brown hair instead. Depending on the breed, this colour might be designated as brown, chocolate or liver. Likewise, the dog’s nose and paw pads will be a lighter brown instead of the usual black.

If the dog is also affected by the D-Locus mutation (genotype d/d), the dog will be lilac or isabella. Note that B-locus mutations only have an effect on dogs that are not genotype e/e on the E-locus, as these dogs cannot produce dark pigment in the first place.