The locus E or extension refers to a mutation in the MC1R gene. Dogs with one or two dominant E alleles produce eumelanin (black pigment) while dogs with two copies of the e^1 allele will have a red or yellow coat. For dogs with at least one E allele, coat colour will be determined by other genes, including the A, B, D and K locus. Two other variants of this mutation were identified in 2018: the e^2 allele found in the Australian Cattle Dog (see DOG-LOCUS-E-CATTLEDOG) and the e^3 allele in the Husky (see DOG-LOCUS-E-HUSKY).
