In each dog two pigments are the basis for their coat colour: black pigment (eumelanin) and red/yellow/cream pigment (pheomelanin). The production of black and red/yellow/cream pigment is controlled by the Melanocortin 1 Receptor (MC1R) gene, also known as Extension gene or E-Locus. The Coat Colour E-Locus (H734) and Coat Colour Em-Locus (H818) combined reveal the genetic status of the E-Locus. The E-Locus has three variants (alleles). The Em allele is dominant over the alleles E and e; allele E is dominant over allele e. The dominant allele Em causes a melanistic face mask. Dogs that are solid black may have the allele Em but the mask is not visible as it is indistinguishable from the body colour. Dogs with white muzzles may have the allele Em but the mask is overridden by white spotting patterns. The Melanistic face mask is present in a variety of breeds (e.g. Afghans, Akitas, Boxers, French Bulldogs, German Shepherds, Great Danes, Greyhounds, Pug Dogs and Whippets). Pug Dogs and Boxers are fixed for the Em allele. The allele E results in a black coat colour and the allele e results in a red coat colour. In Afghan and Saluki hounds a fourth allele has been identified which only is expressed when the dominant black (K-Locus) is not present and the A-Locus is at/at. This fourth allele Eg causes a pattern that is called grizzle or domino. VHLGenetics does not offer a test that detects the Eg allele.
The Coat Colour E-Locus and Coat Colour Em-Locus tests (together E-Locus) enclose the following results, in this scheme the results of the E-Locus are shown in combination with the possible results for the B-Locus:
| E-Locus | Em-Locus | E-Locus (complete) | B-Locus* | Coat Colour |
|---|---|---|---|---|
| E/E | Em/Em | Em/Em | B/B or B/b
b/b |
Black, melanistic mask is not visible
Brown/chocolate/liver, with melanistic mask |
| E/E | Em/N | Em/E | B/B or B/b
b/b |
Black, melanistic mask is not visible
Brown/chocolate/liver, with melanistic mask |
| E/e | Em/N | Em/e | B/B or B/b
b/b |
Black, melanistic mask is not visible
Brown/chocolate/liver, with melanistic mask |
| E/E | N/N | E/E | B/B or B/b
b/b |
Black, no melanistic mask
Brown/chocolate/liver, no melanistic mask |
| E/e | N/N | E/e | B/B or B/b
b/b |
Black, no melanistic mask
Brown/chocolate/liver, no melanistic mask |
| e/e | N/N | e/e | B/B, B/b or b/b | Red/Yellow/Cream |
* Three variants (bs,bc and bd ) of the b-allele are known. Since all three variants result in the same effect, in the above scheme all variants are named b. (B/bc, B/bd and B/bs are in the above scheme B/b. bc/bc, bc/bd/bd/bd, bs/bc, bs/bd and bs/bs are in the above scheme b/b). More explanation about the result > 2b please is available under B-Locus: H733 Coat Colour B-Locus.