This Irish Setter is an example of a dark red coat without dilutions or white patterns. It could carry dominant black KB. Open Source Photo
A dog displaying Kbr. He is KbrKy because his dam was not dominant black or brindle. Although the mask is difficult to see, he is EM and ay at agouti
An example of EM. You can clearly see this dog's dark face mask. This dog will also be ay, due to its fawn coloring. Photo Courtesy of S. McArdle
A wolf displaying the aw agouti allele. You can clearly see the bands of color in the coat. Open Source Photo
Domina, a 75% Afghan, and 25% Saluki dog, displaying the grizzle/domino pheonotype. Photo courtesy of DesertWindHounds.
Colors: Black, Yellow, and Red
Canines produce two types of pigment: eumelanin, which is black pigment; and phaeomelanin which is red/yellow pigment. It is the combination of these pigments, along with dilutions, modifiers, and white patterns, that make up the entire spectrum of dog coat colors.
In dogs and wolves there are four known alleles of the extension locus: EM, EG, E, and e. In the absence of dilutions or white patterns, a dog that is ee will be red or yellow. Its skin and eyes will still be dark, but the coat will only contain red or yellow pigment; thereby producing a red or yellow dog. In an ee dog, many other genes are masked. They are there, and will still be passed on to offspring, but they will not express. Dilutions and white patterns will still affect an ee dog.
If a dog is EM, EG, or E, then it will produce black pigment in its coat. The extent of this black pigment will be determined by other genes.These occur at the K locus and the A locus.
Dominant Black and Brindle
The K locus determines whether a dog is solid black (KB) or brindle (Kbr). As long as the dog is not ee, if it carries KB, the dog will be black. This includes KBKB, KBkbr, and KBky (ky being not black or brindle). This black is often referred to as "dominant black," because it dominates all other colors, with the exception of ee.
If a dog is not ee, and does not carry KB, then many other genes are allowed to express.The EM and EG alleles will be allowed to do something besides turn on black pigment. The EM allele will enable a mask. If the right conditions are met, the EG allele will express the grizzle, or domino, pheonotype. The alleles of the A locus will also be allowed to express, as well as the Kbr (brindle) allele, which organizes black pigment into stripes in the coat.
In the E locus, the order of dominance is: EM, EG,E, and e. It may seem a bit strange that the recessive allele, e, masks the expression of so many other genes; but that is indeed the way it works. For more information about dominant black and brindle see Brindle in Dogs: New Information about Stripes.
Agouti: Fawn, Sable, Wolf, Black and Tan, and Saddle
Dogs have at least four (4) agouti alleles, and more may yet be discovered. These are, in order of dominance: ay, aw, at, and a. There has also been an as allele theorized. But recent evidence presented at the conference on Advances in Canine and Feline Genomics and Inherited Disease in Baltimore, MD (from Sept. 23-25, 2010), seems to indicate it is not a separate allele.
The ay allele will result in a fawn or sable appearance. Clear fawns that do not carry EM can be difficult to distinguish from an ee dog. But they will usually have some black hair, if searched throughly. The ay dogs can be found with and without a mask.
Sable ay dogs will be darker than their fawn counterparts, and the hair is banded with black tips. They can sometimes be difficult to distinguish from the wolf (aw) dog. The Wolf allele (aw) is thought to be the original agouti, and is known as wild type. It is commonly seen in wolves, and is the result of banded hair. Sables can also show banded hair. But unlike a sable, which will show black at the tips, and fawn or red over the rest of the hair, dogs with the wolf allele at agouti will show alternating bands of color along the length of the hair. It is one of the more rare agouti alleles, and can be found with, and without, a face mask.
The at allele is the third agouti allele. Dogs that are atat or ata display the classic "black and tan" or saddle (also known as high tan) phenotype. Dogs that are atat or ata can carry either EM, or be EE or Ee. Black and tan dogs will display a face mask if they carry EM. Black and tan dogs will only display grizzle/domino (EG) if they carry EG and do not carry EM. In fact, a dog must be atat for the grizzle allele (EG) to express. Grizzle (EG) is only present in Saluki and Afghans Hounds. These hounds do not carry the recessive a allele; therefore, they need to be atat to express grizzle/domino. Some black and tan dogs display the phenotype that is referred to as "saddle." In the past, this has been thought of as a separate agouti allele. But as stated above, recent studies have cast doubt on this theory.
The final agouti allele is a. The a allele is only found in a few breeds. It results in what is known as recessive black. Visually, it is indistinguishable from dominant black, but is recessive to all the other agouti alleles. It will only display if homozygous.