Biology Calculator
Coat Color Calculator
Predict the possible coat colors of offspring from two parents using Mendelian inheritance across the base color, extension, dilution and agouti loci. Supports dogs, horses and cats, returning each color with its probability, the most likely outcome, and an optional full genotype breakdown.
Coat Color Calculator
Predict offspring coat colors from parent genotypes
Loci modelled: B, E, D
Carries chocolate and yellow, but not dilution.
Carries chocolate and yellow, but not dilution.
Key Loci — Dog
B — B (black pigment) is dominant over b (brown/chocolate).
E — E allows dark pigment; ee blocks it entirely, producing yellow regardless of B.
D — D is full colour; dd dilutes black to blue and chocolate to lilac.
Results
Select both parent coat colors, then click Predict Coat Colors
Understanding Coat Color Inheritance
Coat color is controlled by several genes, each sitting at a specific position — a locus — on a chromosome. Every animal carries two alleles at each locus, one inherited from each parent, and which alleles are present determines the visible color, or phenotype.
The critical insight is that appearance does not reveal the full genetic picture. Two black Labradors can produce yellow and chocolate puppies because each parent may quietly carry recessive alleles it does not display. This calculator therefore asks for a genotype rather than just a color, because the same black coat can hide very different breeding potential.
Coat Color Probability Formula & Rules
Predicting coat color combines one arithmetic formula with three inheritance rules:
1. Probability Calculation
Each locus contributes four equally likely allele pairings, so a cross across three loci produces 64 outcomes:
2. Dominance Rule
A dominant allele masks a recessive one, so a single copy is enough to show its effect:
3. Recessive Expression Rule
A recessive color appears only when both parents contribute the recessive allele:
4. Dilution Rule
Dilution genes modify the intensity of the base color rather than replacing it:
Practical Impact of Coat Color Genetics
Understanding the genotype behind a coat color matters well beyond curiosity about appearance:
- Informed Breeding Decisions: Knowing which recessives a parent carries predicts which colors a pairing can and cannot produce, so a breeder aiming for a specific color can select mates whose genotypes make it possible rather than relying on appearance alone.
- Teaching Mendelian Genetics: Coat color is one of the clearest real-world demonstrations of dominance, recessive carriers, epistasis and independent assortment, which makes these crosses a standard teaching tool in biology courses.
- Health Linkage Caution: Some color genetics carry health risks — breeding two merle dogs together can produce deafness and blindness, and double-dilute horses have associated concerns. Color should never be selected for at the expense of health screening.
Key Loci Reference by Species
Each species has its own set of genes governing coat color. These are the loci this calculator models:
| Species | Locus | Alleles | Effect |
|---|---|---|---|
| Dog | B | B / b | Black pigment vs brown (chocolate/liver) |
| Dog | E | E / e | ee blocks all dark pigment → yellow |
| Dog | D | D / d | dd dilutes black → blue, chocolate → lilac |
| Horse | E | E / e | ee produces chestnut/sorrel |
| Horse | A | A / a | A restricts black to points (bay); aa is solid black |
| Horse | Cream | D / d | One copy → buckskin/palomino; two → cremello/perlino |
| Cat | B / D / A | B / b, D / d, A / a | Base color, dilution, and tabby vs solid |
Classic Mendelian Cross Ratios
Single-locus crosses follow a small number of fixed ratios. Multi-locus results are these ratios multiplied together:
| Cross | Genotype Ratio | Dominant Shown | Recessive Shown |
|---|---|---|---|
| BB × BB | All BB | 100% | 0% |
| BB × bb | All Bb | 100% | 0% (all carriers) |
| Bb × Bb | 1 BB : 2 Bb : 1 bb | 75% | 25% |
| Bb × bb | 1 Bb : 1 bb | 50% | 50% |
| bb × bb | All bb | 0% | 100% |
| BbEe × BbEe | 9 : 3 : 3 : 1 (dihybrid) | 56.25% both dominant | 6.25% both recessive |
Benefits of Using the Coat Color Calculator
Example Calculations
Here are three scenarios worked out step-by-step:
Example Scenario 1 — Labrador Retriever
Parent 1: Black (BbEe), Parent 2: Black (BbEe).
Both parents carry one chocolate (b) and one yellow (e) allele
B locus cross: Bb × Bb → 1 BB : 2 Bb : 1 bb (75% black pigment, 25% brown)
E locus cross: Ee × Ee → 1 EE : 2 Ee : 1 ee (75% pigment allowed, 25% yellow)
Black = B_ and E_ = 0.75 × 0.75 = 56.25%
Chocolate = bb and E_ = 0.25 × 0.75 = 18.75%
Yellow = ee (any B) = 25%
Result: Black 56%, Chocolate 19%, Yellow 25%
Example Scenario 2 — Horse Bay × Chestnut
Parent 1: Bay (EeAA), Parent 2: Chestnut (eeaa).
E locus cross: Ee × ee → 1 Ee : 1 ee (50% allow black pigment, 50% chestnut)
A locus cross: AA × aa → all Aa (100% agouti, so black is restricted to the points)
Bay = E_ and A_ = 0.50 × 1.00 = 50%
Chestnut = ee (agouti hidden but still inherited) = 50%
Result: Bay 50%, Chestnut 50%
Example Scenario 3 — Dilute Colors
Parent 1: Black carrier (BbEeDd), Parent 2: Blue (BBEEdd).
D locus cross: Dd × dd → 1 Dd : 1 dd (50% full colour, 50% dilute)
Both parents supply dark pigment and allow expression (B_ and E_)
Black = D_ (at least one full-colour allele) = 50%
Blue = dd (two dilution alleles, diluting black to blue-grey) = 50%
Result: Black 50%, Blue 50%
Polygenic Complexity Note
Real coat color is polygenic — far more loci are involved than any simplified model includes. Dogs also have the K (dominant black), A (agouti), S (white spotting) and M (merle) loci; horses have grey, dun, silver, roan and the spotting patterns; cats have the X-linked orange locus that creates tortoiseshell and calico coats. Shade intensity within a single color is set by many small-effect modifier genes. Treat these percentages as expected statistical ratios across many offspring, not predictions for an individual animal, and use genetic testing when the answer actually matters.
Frequently Asked Questions
- How do you calculate coat color probability?
- Count how many genotype outcomes produce each visible color, then divide by the total number of possible outcomes: Probability (%) = (matching outcomes ÷ total outcomes) × 100. For a two-locus cross there are 16 equally likely combinations, so a color matching 9 of them has a 9/16 = 56.25% chance.
- Why do two black Labradors produce yellow puppies?
- Because black parents can each carry a hidden recessive yellow allele (e). A BbEe parent looks black but passes on e half the time. When both parents contribute e, the puppy is ee and cannot produce dark pigment anywhere in its coat, so it is yellow regardless of its B genotype.
- What is the difference between a dominant and a recessive coat color?
- A dominant allele shows its effect with only one copy present, so a single B allele produces black pigment. A recessive color requires two copies — one from each parent — which is why chocolate (bb), yellow (ee) and blue (dd) only appear when both parents contribute that allele.
- How do dilution genes work?
- Dilution does not add a new color; it lightens the pigment already present. In dogs, two copies of the recessive d allele turn black into blue-grey and chocolate into lilac. In horses, the cream allele lightens bay into buckskin and chestnut into palomino, with two copies producing near-white cremello or perlino.
- What does the E locus do in dogs?
- The E (extension) locus controls whether dark pigment can appear in the coat at all. A dog with at least one E allele expresses whatever the B locus specifies. A dog that is ee produces only red or yellow pigment, which masks its B genotype entirely — so a yellow Labrador may be genetically black or chocolate underneath.
- Why is bay the most common horse color?
- Bay requires at least one E allele and at least one A allele, both of which are dominant. Because dominant alleles only need a single copy, the genotype combinations producing bay are far more numerous than those producing solid black (which needs aa) or chestnut (which needs ee).
- Can this calculator predict tortoiseshell or calico cats?
- No. Tortoiseshell and calico patterns come from the X-linked orange locus, which behaves differently from the autosomal loci modelled here and produces sex-dependent results — calico cats are almost always female. This calculator covers the black-series base color, dilution and the agouti/tabby locus only.
- How accurate are these predictions for a real litter?
- The percentages are statistical expectations across many offspring, not guarantees for one litter. A 56% black prediction means each individual offspring has a 56% chance — a litter of four could easily be all black or contain none. Real outcomes also depend on loci this model does not include.
- What does it mean for a parent to be a carrier?
- A carrier displays a dominant color but holds one hidden recessive allele, such as a black dog that is Bb. Carriers look identical to homozygous dominant animals but can produce recessive-colored offspring when bred to another carrier. Genetic testing is the only reliable way to identify a carrier.
- Why does the calculator ask for a genotype instead of just a color?
- Because a single visible color can correspond to several different genotypes with very different breeding outcomes. A black dog that is BBEEDD can never produce chocolate, yellow or blue, while a BbEeDd black dog can produce all three. Selecting the genotype removes that ambiguity from the prediction.