Locus e^A

The e^A locus is responsible for the specific coloration known as the “northern pattern” (domino), most commonly found in northern dog breeds. The most distinctive phenotypic features are a light facial mask and a so-called widow’s peak on the forehead. The resulting coloration is caused by a mutation in the MC1R gene (c.901C>T). This mutation and its phenotypic expression were already identified in prehistoric dog samples dating back approximately 10,000 years to the Holocene in regions of Siberia and southeastern Europe (Ollivier et al. 2013). Selection during the domestication process led to the gradual spread of these now common phenotypic color traits. The domino variant is considered one of the earliest mutations that, through domestication and selective breeding, resulted in decreased eumelanin production and increased pheomelanin expression. Within the hierarchy of the E locus, the e^A allele is recessive to E^M and E, but dominant over e (E^M > E > e^A > e). The resulting coloration is further influenced by the genotypes at the A and K loci. Individuals with genotypes E^M/e^A and E/e^A are carriers of the domino pattern. Specific changes in coloration appear in individuals with genotypes e^A/e^A and e^A/e. The expression of these genotypes differs—individuals with e^A/e may exhibit a lighter pattern compared to those with e^A/e^A. This coloration is referred to as domino (Alaskan Malamute and Spitz breeds), grizzle (Chihuahua), and pied (Beagle).

For clarity regarding the influence of individual loci, the possible genotype combinations and their effects on coloration are typically summarized in tabular form.

Testing for the eA locus is available for all of the following breeds: East Siberian Laika, Finnish Lapphund, Finnish Spitz, Karelian Bear Dog, Lapponian Herder, Nordic Spitz, Siberian Husky, West Siberian Laika, Basenji, Cirneco dell’Etna, Kritikos Lagonikos, Peruvian Hairless Dog (large, medium, and miniature), Basset Fauve de Bretagne, Beagle, Drever, English Foxhound, Finnish Hound, Hungarian Hound, Serbian Hound, Chesapeake Bay Retriever, Pyrenean Mastiff, Chihuahua, Chinese Crested Dog, Phalene, Alaskan Husky, Alaskan Klee Kai, Chinook, Northern Inuit Dog, Tamaskan, Saarloos Wolfdog, and the nearly extinct Berger d’Auvergne (Anderson et al. 2020).