A-Locus (Fawn/Sable; Tricolor/Tan Points; Solid Black)

Description

There have been four different alleles identified in a dog’s genes that signal the agouti coloration (this coloration can be exemplified as the coloration of the wild brown rabbit), also known as the A-locus. If you’d like to learn more about the difference between an allele and a gene, click here. These alleles are a^y, a^w, a^t, and a.

These alleles are dominant in a hierarchy. This means that a^y is more dominant than a^w, a^w is more dominant than a^t, and a^t is more dominant than a. For example, if a dog has a^ya^t, the color associated with a^y will appear on the dog, rather than the color associated with a^t. However, this is all dependent on whether or not the dog carries the dominant black gene at the K-locus or the recessive gene on the E-locus. You can learn more about how the genes interact with one another by reading the flow chart we have provided. If a dog carries one or both of these genes, the A locus is muted and the agouti coloration will not appear on the dog. This is because both the K locus and the E locus are dominant over the A locus.

The Agouti gene (A-Locus) determines the base coat color in dogs that are k^y/k^y for dominant black. Dogs must be k^y/k^y in order to express any alleles on the A-Locus. The color of the dog can still be modified by other genes, such as by the B-Locus or D-Locus, however. For example, if a dog is b/b (recessive) for the B Locus, they will still have areas that are pigmented as black. However, it will be modified to appear as a chocolate pigment.

However, if a dog’s A locus codes for the fawn coloration and the dog is b/b for the B locus, the fawn dog will have a chocolate nose. In contrast, a dog that is a^t/a^t will have a chocolate and tan coat, rather than black and tan. If a dog is n/n for a gene, that means that the dog is recessive for this gene and the typical colors associated with the pattern are not expressed. This is a generic term used to refer to the expression of any coat color.

The "a^y" Allele

The a^y allele is the most dominant of all four alleles on the A-locus. The a^y gene produces a range of coat colors like light fawn colors, darker red colors, or even a sable. This variation of color is due to variances in the expression of this gene. Dogs that are k^y/k^y for the K Locus and have one or two copies of the a^y allele will always express the a^y coat pattern. This is because the a^y allele is more dominant than the k^y allele expression. It is important to note, however, that a dog can appear as fawn or sable and could also carry any other of the three alleles. These other alleles, however, would not be expressed, and a person wouldn’t be able to tell the dog had the other alleles based on looks.

This does not mean that the dog with a fawn coat (a^y) will always pass on a copy of the a^y allele or the coat color that the parent has. A dog that is a^y/a^w, a^y/a^t, or a^y/a has a 50% chance of passing on the a^y allele and a 50% chance of passing on the other alleles. A dog that has two copies of the a^y allele will always pass on the a^y allele. As long as that dog is bred to another dog that is n/n (recessive) for the K-Locus, the dog will always produce fawn or sable pups.

The "a^w" Allele

The a^w allele produces a color known as "wild sable." This coat coloration is sometimes called the "wild type," or in some breeds, "wild boar." With this coloration, the hairs switch pigmentation from a black color to a reddish or fawn color. This color is sometimes seen in German Shepherds and other shepherd breeds. It is recessive only to the a^y allele. This also means that it is dominant to the a^t and a alleles, and will be expressed before the a^t and a alleles.

If a dog is n/n for the a^y allele (meaning this allele is not expressed), a dog with one or two copies of the a^w allele will express the a^w coloration. A dog that is n/n for a^y and has one copy of the a^w allele can carry either the a^t or "a" allele and not express them. However, even though the a^t and “a” alleles do not appear on the coat, either allele can be passed to any offspring.

The "a^t" Allele

Both the "black-and-tan" and "tricolor" phenotypes (expressed traits) are caused by the a^t allele. A tricolor dog is black-and-tan, with white. White is generally just an absence of color, rather than a pigment the dog expresses. For a dog to be black-and-tan or tricolor, he must be n/n for the dominant black gene (the K-Locus). This means that the K-Locus is not expressed, and the dog will not be black. Furthermore, the dog must have either two copies of the a^t allele, or have one copy of the "a^t" allele and one copy of the "a" allele.

The dog must be n/n for both the a^y and a^w alleles in order for a^t to be expressed. This is because the a^y and a^w alleles are dominant over a^t. A dog that is a^t/a^t will always pass on a copy of the a^t allele to any offspring. This does not ensure that the puppies will be black-and-tan. However, the coat color of the offspring also depends on the genotype of the other parent.

The "a" Allele

If a dog is k^y/k^y on the K-Locus, the dog must be n/n for a^y, a^w, and a^t in order for the dog to express the a/a coloration. A dog that is solid black with the recessive K locus must also have the recessive a/a allele in order to express the black coloration. It is important to make this distinction because a dog can also be solid black with k^B/k^B or k^B/k^y under the K-Locus. The A locus is not needed for this type of dog. Therefore, this type of black dog does not need the a/a coloration in order to express the black color. You can learn more about this type of dog by reading about the K-locus or the B-locus.

This is also the case for dogs that are bicolor, and are negative for K-Locus (k^y/k^y). This is generally the cause of a solid black German Shepherd. The "a" allele is sometimes referred to as the recessive black gene. Because this allele is the most recessive, for a dog to express this phenotype he must have two copies of the "a" allele and be n/n for a^y, a^w, and a^t. A recessive black dog will always pass on the "a" allele to all offspring.