Ayat can resemble the awaw phenotype. Other genes also affect how much black is in the coat. aw is the only allele present in many Nordic spitzes, and is not present in most other breeds. at includes tan point and saddle tan, both of which look tan point at birth. Modifier genes in saddle tan puppies cause a gradual reduction of the black area until the saddle tan pattern is achieved. a is only present in a handful of breeds. Most black dogs are black due to the K locus allele KB for dominant black. Border Collies is one of the few breeds that lack agouti patterning, and only have sable and tan points. However, many border collies still test to have agouti genes. E (extension) locus The alleles at the E locus (the melanocortin receptor one gene or MC1R) determine whether an animal expresses a melanistic mask, as well as determining whether an animal can produce eumelanin in its coat. There are three known, plus two more theorized, alleles that occur at the E locus: Em = Mask (a eumelanin mask is added to the face). The distribution of the pigments on the rest of the face and on the body is determined by the agouti locus. EG = Grizzle (if atat and not KB/-, tan underparts with a dark overlay covering the top and sides of the body, head and tail, and the outside of the limbs) - also called domino. Ed = Northern Domino (functions and appears similar to Grizzle in sighthounds) found mostly in Northern breeds such as the Siberian Husky and Finnish Lapphund, as well as Native breeds like the Chihuahua who are descended from primitive spitz breeds brought across the Bering Strait. E = Normal extension (pattern expressed as per alleles present at A and K loci). eh = Cocker sable (if KB/- and may require atat, tan with a dark overlay covering the top and sides of the body, head and tail, and the outside of the limbs). e = Recessive or clear fawn (tan, inhibition of eumelanin). e2 = Found only in the Australian Cattle Dog, this gene creates the cream color in this breed. e3 = Found only in Nordic breeds, this gene creates the white and yellow coat color. The dominance hierarchy for the E locus alleles appears to be as follows: Em > EG/d > E > eh >