Dog Coat Color Genetics Calculator

How 8-Locus Dog Coat Color Inheritance Works

Canine coat colors are governed by unlinked autosomal gene loci interacting epistatically. All colors derive from two pigments: black eumelanin and yellow/red phaeomelanin.

The 8 Major Loci Explained:

• A Locus (ASIP - Agouti): Determines whether the coat has fawn pigment (ay), tan points / black and tan (at), or recessive black (a).
• B Locus (TYRP1 - Brown / Chocolate): Recessive b/b turns black coat, nose, and foot pads into testable chocolate.
• co Locus (Cocoa): French Bulldog cocoa chocolate mutation. Recessive co/co produces chocolate base. Dogs with b/b co/co are Double Chocolate.
• D Locus (MLPH - Dilute): Recessive d/d dilutes black to blue, and dilutes chocolate to lilac or isabella!
• E Locus (MC1R - Extension & Mask): Em produces melanistic facial mask. Recessive e/e causes cream/red (masking all dark pigment, producing Platinum Frenchies).
• K Locus (CBD103 - Dominant Black): KB forces solid eumelanin; ky/ky allows tan points (A-locus) to show.
• M Locus (PMEL - Merle): M/m produces merle/dapple marbling. Never breed two visual merles together.
• L Locus (FGF5 - Fluffy / Long Hair): Recessive l/l produces long hair (Fluffy French Bulldogs and long-haired Bullies).

Commercial DNA Test Lab Translation Matrix

Different genetic testing laboratories use slightly different allele symbols. Below is the cross-reference translation table between major veterinary testing laboratories:

The Epistasis Hierarchy: How Canine Coat Color Genes Interact

In canine coat color genetics, genes do not operate in isolation. Instead, they interact through a biological phenomenon known as epistasis, where the expression of one gene locus masks or alters the phenotypic expression of alleles at entirely separate gene loci. To accurately predict the visual appearance (phenotype) of puppies from parental DNA genotypes, professional breeders and veterinary geneticists must evaluate loci in a strict hierarchical order:

Rare Color Combinations & DNA Genotype Formulation Table

In specialized breeds such as French Bulldogs, English Bulldogs, American Bullies, and Poodles, specific combinations of recessive alleles produce highly valued coat varieties. The following reference table outlines the required multi-locus genotypes for visual presentation:

Step-by-Step Mendelian Calculation Example: Predicting an Isabella Litter

To understand how the calculator evaluates complex multiple-locus pairings, consider a realistic breeding scenario between two health-tested French Bulldogs:

Because both parents are homozygous for Co/Co (non-cocoa), ky/ky (tan point permissive), and at/at (tan points), every puppy in the litter is guaranteed to express tan points. The segregation of colors depends entirely on the independent assortment of alleles at the B locus and D locus:

1. B Locus Segregation (Brown):
   Cross: b/b (Sire) × B/b (Dam).
   Offspring probabilities: 50% B/b (Black base carrying chocolate), 50% b/b (Visual testable chocolate base).
2. D Locus Segregation (Dilute):
   Cross: D/d (Sire) × d/d (Dam).
   Offspring probabilities: 50% D/d (Non-dilute carrier), 50% d/d (Visual dilute).
3. Joint Probability Calculation via Product Rule:
   Because the B locus on canine chromosome 11 and the D locus on canine chromosome 25 assort independently:
   • Isabella Tri (b/b d/d): $0.50 \times 0.50 = \mathbf{25.0\%}$ (Visual champagne taupe with tan points).
   • Testable Chocolate Tri (b/b D/d): $0.50 \times 0.50 = \mathbf{25.0\%}$ (Visual chocolate carrying dilute).
   • Blue Tri (B/b d/d): $0.50 \times 0.50 = \mathbf{25.0\%}$ (Visual blue carrying chocolate).
   • Black & Tan Tri (B/b D/d): $0.50 \times 0.50 = \mathbf{25.0\%}$ (Double carrier for chocolate and dilute).

The litter delivers an exact 1:1:1:1 phenotypic ratio, offering a 25% yield of the highly coveted Isabella Tri color while guaranteeing that 100% of the non-isabella puppies carry both valuable recessive alleles.

Understanding Complex Alleles: Merle SINE Lengths and S Locus Spotting

Beyond standard single-nucleotide polymorphisms, canine coat genetics involves mobile genetic elements and structural variants that demand careful interpretation:

The PMEL Merle Allelic Spectrum

The Merle gene (PMEL17) is not a simple binary on/off switch. It is caused by the insertion of a Short Interspersed Nuclear Element (SINE retrotransposon) containing a poly-A tail of varying length. The length of this base-pair insert directly determines the degree of pigment deletion and auditory risk:

• Cryptic Merle (Mc, 200–230 bp): Does not exhibit visual merle marbling and does not cause hearing or ocular deficits even when paired with classic merle.
• Atypical Merle (Ma, 231–254 bp): Muted dilution without distinct patches; minimal ocular risk.
• Classic Merle (M, 255–268 bp): Classic torn-paper patched marbling with blue ocular marbling.
• Harlequin Merle (Mh, 269–280 bp): Dramatic pigment removal leaving stark white backgrounds with torn dark patches. Extreme sensory risk if doubled.

The S Locus (MITF) and White Spotting Risks

The S locus encodes the Microphthalmia-Associated Transcription Factor (MITF). The wild-type allele S produces full pigment coverage, whereas the recessive piebald allele sp blocks melanoblast migration from the neural crest during embryogenesis. Dogs with sp/sp exhibit more than 50% white body coverage (piebald). When melanocytes fail to populate the stria vascularis in the inner ear cochlea, permanent congenital deafness ensues. Breeders selecting for extreme piebald markings must routinely perform Brainstem Auditory Evoked Response (BAER) testing on all litters.

Frequently Asked Questions About Dog Coat Color Genetics