Coat with tan points

The ASIP gene is a relevant gene in determining the coat color pattern. The at allele is associated with a dark colour pattern combined with tan dots.

Definition

The tan spotted coat trait creates a colouring pattern characterised by a dark coloured coat (black or brown) with tan spots on the underside of the legs, eyebrows, muzzle, chest and under the tail. However, there may be variations in the intensity and distribution of the color. 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 is produced instead of eumelanin.

Genetic basis

The variant is also known as the allele "at" in the ASIP gene. In this gene, an allelic series has been described (Ay > aw > as > at > a), according to which, the at allele shows dominance over the wild-type allele. This dominance implies that a single copy of the variant is sufficient to express the associated phenotype. Meanwhile, the remaining variants exhibit dominance over the at allele. If a dog carries a single copy of the at allele, there is a 50% chance that the variant will be inherited by its offspring. Additionally, it is important to note that there may be other, as yet unknown genetic factors involved in the development of the trait.

Other relevant information

For the expression of this coloration pattern it is necessary that the dog is neither black dominant at locus K nor red recessive at locus E. Dogs showing a black and tan coloration pattern are born with the phenotype corresponding to the trait coat with tan points. The trait is also called black-black or tricolor when white is also expressed. The trait is commonly present in the breeds Airedale Terrier, Basset Hound, Beagle, Beauceron, Boxer, Doberman Pinscher, German Shepherd Dog, Rottweiler, Silky Terrier and Welsh Terrier.

Bibliography

Dreger DL, Schmutz SM.A SINE insertion causes the black-and-tan and saddle tan phenotypes in domestic dogs. J Hered. 2011 Sep-Oct;102 Suppl 1:S11-8.