Genetic basis of e2 allele - is a variant of the MC1R gene at the E locus. It is specifically found in Australian Cattle Dogs and produces a cream coat color variant distinct from the common recessive red allele (e1). The mutation causing e2 is c.-432G>C (a change in the promoter region or regulatory region of the gene), which leads to altered MC1R function and reduced eumelanin production. This allele results in a loss-of-function of the MC1R receptor impacting pigment production similarly to other recessive red alleles but with subtle differences in coat color expression.
Pathophysiology - The loss-of-function mutation prevents normal signaling that stimulates eumelanin (black/dark pigment) production. Therefore, dogs homozygous or compound heterozygous for e2 and other loss-of-function alleles (e1) produce mainly phaeomelanin (red/yellow pigment). The e2 allele causes a cream or pale red coat color that is often non-standard compared to classic red or yellow caused by e1.
Complications - No direct health problems are related to the e2 allele. The allele only influences coat pigment production.
Clinical Presentation - Coat colors vary from cream to pale red/yellow in Australian Cattle Dogs carrying the e2 allele. Dogs with e2/e2 or e1/e2 genotypes typically have lighter coats. The diluted phenotype is sometimes confused with other dilution or pale color genes but genetically distinct.
Inheritance - The e2 allele is recessive, expressed in homozygous e2/e2 or compound heterozygous e1/e2 genotypes. Dogs with one copy of e2 and one copy of dominant E alleles will have normal eumelanin pigmentation. The presence of e2 can modify coat color expression in combination with other loci like K and A.
Why This Matters to Breeders and Vets - Identifying the e2 variant improves breed-specific coat color prediction and helps breeders manage or select for desired coat colors. Genetic testing for e2 alongside other MC1R variants supports informed breeding decisions and maintains genetic diversity.
