A, K and E locus

I am asked frequently why two solid colored dogs can have tanpoint offspring. That’s why I wrote this article, which should clarify the interaction between the gene loci A, K and E.

Imagine the color of a dog like a painting on a canvas. In this imagination, the gene loci A, K and E represent the layers of color applied on top of each other.

While gene loci A, K and E represent the layers of color applied on the canvas, gene loci B and D can be compared to different paint. In principle, there are two “paint types”: black color (eumelanin) and yellowish color (pheomelanin). If a dog has genotype d/d on the D locus, some “blue diluent” is mixed into the eumelanin. If it has genotype b/b, some brown diluent is mixed into the eumelanin. If the dog has both d/d and b/b, both “thinners” are mixed into the eumelanin, the picture is painted with a beige eumelanin in that case.

The A locus represents the first layer of paint. Depending on the genotype at the A locus, a specific color distribution of pheomelanin and eumelanin is applied to the canvas here. So, with the genotype at/at, the picture of a “tanpoint” dog is created: eumelanin on the body, and pheomelanin on the tan markings.

The K locus represents the second layer of paint. If the genotype here is KB/KB, a uniform color layer of eumelanin is applied over the first layer.

In case of ky/ky, the second color application consists of a layer of “clear lacquer”.

In case of KB/ky, there are two possibilities: Either the dominant KB is layered over the first color layer as in the KB/KB genotype. Or – if a brindle factor is added – a stripe-like pattern of eumelanin stripes overlies the first color application. Since it is not yet possible to test for the brindle factor, there is currently no way to find out by genetic testing whether a dog with the KB/ky genotype is simply heterozygous dominant black or whether it carries the brindle factor.

The E locus now represents the third layer: If a dog has genotype e/e here, a third color layer of pheomelanin is applied. Genotype E/E (or E/e), on the other hand, means a layer of “clear lacquer”.

So, it is also understandable that every dog (also a yellow Labrador, a brown German Shorthair Pointer or a Weimaraner) has three “layers” (i.e. a genotypes) at all these three gene loci.

Depending on the genotypes of the parents, it can also happen that black-and-tan or even black-and-brindle puppies derive from purebred solid Labrador Retrievers or tanpoint puppies derive from two solid Weimaraners – as in these two examples:

This is a black-and-brindle Labrador puppy from yellow and brown parents.

This is a tanpoint Weimaraner.

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