K Locus (Dominant Black), Agouti Expression Locus, Dominant Black Coat Color, K Locus, KB Locus, ky Locu
A mutation in K Locus (CBD103 gene) known as the K-KB allele allows the production of black pigment (eumelanin) by preventing A Locus expression which would normally block the production of black pigment. The naturally occurring version of the K Locus gene that lacks a mutation normally functions to allow for A Locus gene expression which inhibits black pigment synthesis. The K-KB mutation is referred to as dominant which means only one copy of the mutation is required to inhibit A Locus gene expression and result in a black coat coloring commonly referred to as “Dominant Black”. Dogs with one or two copies of the mutation will not express A Locus coat colors (sable/fawn, tricolor, black and tan, or tan points) and their coat color will be solid in pigmented areas with the final coat color determined by the E and B Loci. Dogs that test “Clear” for the K-KB mutation allow A Locus gene expression and can produce puppies with sable/fawn, tricolor, or tan points depending on the mutations present at the A locus.
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These dogs have two copies of the normal K Locus gene, which allows for A Locus expression and can result in a variety of coat colors including sable/fawn, tricolor, tan points, black or brown. The coat color for dogs with a normal K Locus gene is dependent on its genotype at the E, A and B Loci and they will not pass the K-KB mutation to their offspring.
These dogs have one copy of the normal gene and one copy of the K-KB mutation that leads to black coloring in pigmented areas of the dog. They can have a black-based coat and will, if bred, pass the mutation to 50% of its offspring, on average. This dog’s coat color is also dependent on its genotypes at the E and B Loci.
C. (AT RISK/AFFECTED):
These dogs have two copies of the mutation that allows black coloring in pigmented areas of the dog and will pass the mutation to 100% of its offspring. This dog’s coat color is also dependent on its genotypes at the E and B Locus genes.
Autosomal Dominant Dependent On E Locus And B Locus
C.231_233del (3 Bp Deletion)
Candille SI, Kaelin CB, Cattanach BM, Yu B, Thompson DA, Nix MA, Kerns JA, Schmutz SM, Millhauser GL, Barsh GS. A β-defensin mutation causes black coat color in domestic dogs. Science. 2007 Nov 30; 318(5855):1418-23. [PubMed: 17947548]