Recessive red coat

The recessive red coat consists in the expression of a reddish coat that can vary in shade from red to cream or even white.

Definition

The recessive red coat trait refers to the expression of pheomelanin (red pigment) in all pigmented areas of the dog. The shade of the pigment is variable, therefore, the dog's coat can be red, apricot/orange, yellow, ivory, cream or even white. The variant responsible for the coloration trait is located in the MC1R gene (also known as the extension locus or E locus) which is involved in the switch from pheomelanin to eumelanin (black/brown pigment) production in melanocytes. Thus, the MC1R gene is also involved in determining the dark color of the entire coat of the dog.

Genetic basis

The recessive red coat trait, also known as the "e" allele, is inherited recessively. Therefore, the presence of two copies of the c.916C>T variant is required for a dog to have a red coat. If only one copy of the c.916C>T variant is present, the dog can still express eumelanin, but this does not necessarily mean that the coat is black/brown, as the pigmentation of the coat depends on other loci such as A, B and K. In this case, there is a 50% chance that the offspring will inherit that single copy of the variant. There are also other variants that cause loss of function of the E locus. If you combine a copy of one of these variants with a copy of the variant described here (compound heterozygosity), you will get the recessive red coat phenotype. However, the exact coat colour cannot be determined by studying this variant, as the intensity of the pigment is determined by other genes.

Other relevant information

The described variant causes the loss of function of the MC1R gene, and consequently, melanocytes produce only pheomelanin, since they do not receive any instruction to substitute the production of pheomelanin for that of eumelanin. Thus, the recessive red color is imposed on any coloration pattern that requires eumelanin expression. Dogs with recessive red coloration often show white whiskers and loss of nose pigmentation (also known as "snow nose"). Other names for the trait include yellow, champagne, cinnamon, lemon, apricot, golden, beige, orange or tan coat color. Breeds commonly showing the trait are Irish Setter, Labrador Retriever, Bichon Frise, Golden Retriever, American Eskimo Dog, Vizsla and Samoyed.

Bibliography

Everts RE, Rothuizen J, van Oost BA. Identification of a premature stop codon in the melanocyte-stimulating hormone receptor gene (MC1R) in Labrador and Golden retrievers with yellow coat colour. Anim Genet. 2000 Jun;31(3):194-9.