The phenotypic expression of canine coat color is dictated by complex molecular interactions across several genetic loci that control the production and distribution of two melanin pigments: eumelanin (black/brown) and phaeomelanin (red/yellow). The Extension (E) locus encodes the Melanocortin 1 Receptor (MC1R). A dominant E allele allows the production of eumelanin, while a homozygous recessive 'ee' genotype blocks eumelanin, resulting in a solid phaeomelanin (red/yellow) coat, as seen in Golden Retrievers. If eumelanin can be produced, the Agouti (A) locus, which encodes the Agouti Signaling Protein (ASIP), dictates the distribution of the black and red pigments (e.g., sable, wolf sable, or tan points). Furthermore, the Brown (B) locus encodes Tyrosinase-Related Protein 1 (TYRP1); recessive 'bb' mutations alter the structure of eumelanin, diluting black pigment to a brown/chocolate color, famously observed in Chocolate Labs.