EM-Locus

Mutation in melanocortin 1 receptor is responsible for the development of black melanistic mask in some dog breeds. Mask appears due to eumelanin production in the region of the muzzle, eyebrows, and ears and can even spread to the pectoral and dorsal area. Dominant mutated allele is named E^M. Mask is expressed in homozygous (E^M/E^M) and heterozygous dogs (E^M/E^X). Homozygous dogs will have puppies with masks regardless of genotype of the other parent. In some dogs, although they carry the mutation, mask is not visible due to coat colour. Mask is visible in fawn/sable (Great Dane, German Shepherd) and brindle dogs (Boxer). Mask is not visible in dogs with black, chocolate/liver or blue coat colour. In such cases mask can become partially visible due to age related greying on the rest of the body. In addition, dogs with white muzzles sometimes do not show mask. Although mask is not visible dog can transfer mask allele to its offspring.