Canine Genetics & Health Testing
A plain-English reference to dog coat color genetics from a breeder who DNA tests every breeding dog. Each locus below has its own page covering alleles, dominance, interactions with other loci, breed examples and frequently asked questions.
The Loci
- E Locus: Extension (MC1R): The master switch that decides whether a dog's coat shows black-based pigment (eumelanin) or red/yellow pigment (phaeomelanin) — and whether a black facial mask is present.
- A Locus: Agouti (ASIP): Controls how black and red pigment are distributed across the body — producing sable, wild agouti, tan points (phantom), or recessive black. Only visible when the K and E loci allow it.
- K Locus: Dominant Black (CBD103 (β-defensin) & brindle modifier): The gatekeeper for the A locus — decides whether a dog shows solid color, brindle stripes, or an agouti pattern like sable or tan points.
- B Locus: Brown / Liver (TYRP1): Turns black pigment into brown (chocolate/liver) when a dog carries two recessive copies. Affects the entire eumelanin pigment system — coat, nose, paw pads, eye rims, and eye color.
- D Locus: Dilute (MLPH): Lightens eumelanin pigment: black becomes blue/grey and chocolate becomes lilac/isabella. Also potentially lightens phaeomelanin. Two copies of the recessive d allele are required.
- S Locus: White Spotting (MITF): Determines solid versus parti/piebald — the amount and placement of white on the coat, from a small chest spot to mostly white with colored patches.
- M Locus: Merle (PMEL (SILV)): Creates the mottled merle pattern through a variable-length DNA insertion. The insertion length determines patterning intensity — and breeding two merle dogs together risks producing double merles with serious deafness and blindness.
- Coat Genes: Furnishings, Curl & Shedding (RSPO2 · KRT71 · MC5R): The genes behind the 'teddy bear' doodle look — the beard and eyebrows (furnishings), the wave or curl (curl gene), and how much a dog sheds (MC5R shedding gene). Critical for families seeking low-shedding or allergy-friendly coats.