K-KB Locus (K-KB Locus)
A mutation in K Locus (CBD103 gene) known as the K-KB allele allows production of black pigment (eumelanin) by preventing A Locus expression which would normally block production of black pigment. The naturally occurring version of the K Locus gene lacking 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 KB 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 K-KB 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 allows A Locus gene expression and can produce puppies with sable/fawn, tricolor, or tan points depending on the mutations present at the A locus.
A (CLEAR/NORMAL): 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.
B (CARRIER/AFFECTED): 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.