The Beta-defensin gene (CBD103 gene) produces dominant black vs. brindle vs. fawn coat colours. This gene is also known as the K-locus or Dominant black gene. The coat colour is further complicated by the interaction with the E-locus and the A-locus (agouti). The Coat Colour K-Locus (H819) tests for the genetic status of the K-Locus. The K-locus has three variants (alleles). The allele KB is dominant over the alleles kbr and ky; allele kbr is dominant over allele ky. The dominant allele KB, also called dominant black allele, does not allow the agouti gene to be expressed. A dog with at least one copy of the KB allele expresses a base colour, which is determined by the B- and E-Locus. The allele kbr results in brindling and allows the agouti to be expressed but causes brindling of the agouti patterns. The A-Locus (agouti) represents several different colours, such as fawn/sable, wild sable, tan points and recessive black. The allele ky allows the agouti to be expressed without brindling. When a dog has two copies of the ky allele (homozygous ky/ky) the agouti locus determines the dog’s coat colour. The test does not discriminate between the alleles kbr and ky.
The Coat Colour K-Locus test encloses the following results:
| K-Locus | Coat Colour |
|---|---|
| KB/KB | Self-colored (solid color in pigmented areas), hides expression of the A-locus, basic colour determined by B- and E-locus, only allele KB will be passed on to an offspring |
| KB/N | Self-colored (solid color in pigmented areas), hides expression of the A-locus, basic colour determined by B- and E-locus. The test does not discriminate between the alleles kbr and ky, N can be allele kbr or ky. The dog is KB/kbr or KB/ky, either allele KB or kbr/ky will be passed on to an offspring |
| N/N | The test does not discriminate between the alleles kbr and ky. N can be allele kbr or ky. The dog is kbr/kbr, kbr/ky or ky/ky. If the dog is kbr/kbr: Brindling and expression of A-locus, it can only pass on allele kbr to an offspring. If the dog is kbr/ky: Brindling and expression of A-locus, either allele kbr or ky will be passed on to an offspring. If the dog is ky/ky: Expression of A-locus without brindling, only allele ky will be passed on to an offspring. |