Fawn coat

The Ay allele in the ASIP gene is associated with the development of a coat coloration known as "fawn", which is characterized by a red or yellow base with darker colored tips.

Definition

The fawn coat is characterized by expressing a base coloration of reddish or yellowish hue with dark colored tips due to a variant described in the ASIP gene (known as locus A). This gene favors the expression of pheomelanin (red pigment) over eumelanin (black pigment) by interacting with and inhibiting the action of the MC1R gene. The MC1R gene induces the expression of enzymes responsible for eumelanin synthesis. The variant associated with this coat type is classified as a gain-of-function variant of the ASIP gene, resulting in a preference for the expression of red coloration (pheomelanin).

Genetic basis

The fawn coat trait is also known as the "Ay" allele. The inheritance is dominant over the other variants described at the same locus (Ay > aw > as > at > a). Therefore, the expression of one or two copies of the variant is sufficient for the manifestation of the fawn coat. However, due to the complex gene interaction that exists in the determination of canine coat color, other loci such as K and E can interfere and mask the expression of this coloration.

Other relevant information

Dogs carrying the Ay allele show a variable expression of dark hair color. Some dogs show hardly any dark hairs, showing a phenotype closer to the recessive red trait, while others show a greater number of dark hairs, giving their phenotype a resemblance to the wild-type coat. It is suggested that this variability could be attributed to various epigenetic mechanisms. This trait is also known by other names, such as sable or yellow dominant.

Bibliography

Berryere TG, Kerns JA, Barsh GS, et al. Association of an Agouti allele with fawn or sable coat color in domestic dogs. Mamm Genome. 2005 Apr;16(4):262-72.