recently named the K locus. In Labradors a highly-active mutated version of the K gene, (K^B) is invariant, producing uniform eumelanin distribution independent of the Agouti genotype and leaving differences in MC1R to mediate the sole variability of this signaling pathway.

A recessive mutation in this E gene truncates the protein, producing a non-functional receptor incapable of directing eumelanin deposition in the fur. Among dogs, this mutation is unique to yellow