Melanocortin 1 receptor (MC1R) on E locus is responsible for regulation of pigment production in melanocytes. Mutation inMC1R gene results in non-functional receptor and switches pigment production to pheomelanin. Because production of eumelanin is disabled, effect of other loci is not possible. Mutation is recessive therefore, two such alleles are necessary for yellow-red (pheomelanin) coat colour expression. Different dog breeds with genotype e/e express different colour shades from light cream (Golden Retriever) to deep red (Irish Setter). E locus does not interfere with pigment production on pads, nose and eyes (regulated by B locus).
Dominant normal E allele allows production of eumelanin therefore, all homozygous (E/E) and heterozygous (E/e) dogs will be either black or other colour, if other loci are expressed (B, A and K locus).
|E/E:||dog is homozygous for normal allele; normal eumelanin production, expression of other loci can determine coat colour.|
|E/e:||dog is heterozygous; because E allele is dominant eumelanin production is normal and expression of other loci can determine coat colour; dog is a carrier of recessive mutation and will transfer it to 50% of its offspring.|
|e/e:||dog is homozygous for e allele; only pheomelanin is produced; dog expresses light cream to dark red coat colour.|