The B (brown) locus refers to a mutation in the TYRP1 gene causing the brown colour of the coat, also called liver or chocolate. The black (B) allele is dominant over the brown alleles (bs, bd, bc). For red or yellow dogs, the brown allele will not change the colour of the coat, but will change the colour of the nose and the pads of the paws. Other mutations can cause brown coat colour in the Australian Shepherd (DOG-LOCUS-B-BGAUST) and Lancashire Heeler (DOG-LOCUS-B-LHEELER). This test does not detect the mutation for chocolate (DOG-COCOA) in French Bulldogs.
