Recessive black coat

The recessive black coat is a trait characterized by a solid coloration of black hair or with small reddish spots.

Definition

The recessive black coat trait corresponds to a coat that expresses mainly eumelanin (black pigment) resulting in a solid black coloration or with small reddish markings. The variant is located in the ASIP gene (known as locus A) which encodes a protein that inhibits the activation of the MC1R gene. Consequently, in melanocytes where MC1R is inactivated, pheomelanin (red/yellow pigment) is produced instead of eumelanin.

Genetic basis

The recessive black coat trait is also known as the "a" allele. As the name of the trait indicates the type of inheritance is recessive, for this reason, the presence of two copies of the c.286C>T variant is required for the dog to show a black coat. In addition, due to the complex gene interaction that exists in the determination of coat color, it is necessary that the dog is neither red recessive ("e" allele) nor black dominant ("KB" allele) for the recessive black coat trait to be expressed.

Other relevant information

The described variant causes the ASIP gene to lose its function, and therefore, only eumelanin is produced in the melanocytes, since the MC1R gene is activated correctly. The expression of black coat color caused by this variant is not very common. In addition to the involvement of the K and E loci, discussed previously, there may be other loci that modify the final phenotype of the dog, such as the B locus. Breeds that may have the trait are American Bully, Australian Shepherd, Basenji, German Shepherd Dog, Giant Schnauzer, Newfoundland, Pomeranian, Portuguese Water Dog, Samoyed, Scottish Terrier and Wirehaired Pointing Griffon.

Bibliography

Kerns JA, Newton J, Berryere TG,et al. Characterization of the dog Agouti gene and a nonagoutimutation in German Shepherd Dogs. Mamm Genome. 2004 Oct;15(10):798-808.