Canine Coat Color Genetics: A Breeder's Guide to Predicting Puppy Coat Colors and Patterns

A dog's coat color and pattern are determined by a handful of well-studied genes, each located at a specific locus on the chromosome. At every locus a dog carries two alleles — one inherited from the sire and one from the dam. Some alleles are dominant and mask the effect of others, while recessive alleles only show their effect when a dog carries two copies. When two dogs are bred, the combination of alleles their puppies can inherit follows predictable Mendelian probabilities, which is exactly what a coat color genetics calculator computes.

The major loci include the E (Extension) locus, which controls whether dark eumelanin can be produced at all; the K (Dominant Black) locus, which can override the agouti pattern; the A (Agouti) locus, responsible for saddle, tan point and fawn patterns; the B (Brown) locus, which turns black pigment to liver; and the D (Dilution) locus, which lightens pigment to blue or lilac. Additional loci control white spotting, merle, roan, ticking, furnishing and curl, each adding another layer to the final appearance of the coat.

Genes do not act in isolation. One locus can mask or modify the effect of another — a relationship called epistasis. For example, a dog that is recessive red (e/e) at the E locus will appear red or cream regardless of what it carries at the K or A loci, because the e allele switches off the production of dark eumelanin pigment. Similarly, the dominant black allele (KB) at the K locus hides the agouti patterns controlled by the A locus, so a KB/KB or KB/ky dog will be solid black even if it carries the genes for tan points.

The B and D loci modify pigment rather than creating new colors. A B locus dog with two recessive b alleles turns all black eumelanin to liver (brown), and a D locus dog with two recessive d alleles dilutes pigment — black becomes blue and liver becomes lilac. Because these effects stack, a single dog can carry the genes for black, liver, blue and lilac simultaneously, and a breeding between two hidden carriers can produce puppies of colors neither parent visibly shows. This is why a true genetic prediction requires the full genotype of both parents, not just their visible color.

To predict the coat colors of a litter, a genetics calculator builds a Punnett square for every locus. Each parent can pass one of its two alleles to a puppy, so a heterozygous parent (for example E/e) passes each allele 50% of the time, while a homozygous parent (E/E or e/e) passes the same allele 100% of the time. Multiplying the per-locus probabilities together produces a full joint genotype distribution for the litter — the chance of every possible combination of alleles across all loci.

Each joint genotype is then translated into a visible phenotype using the dominance and epistasis rules described above. Different underlying genotypes can produce the same visible coat, so identical phenotypes are grouped together and their probabilities added up. The result is a ranked list of predicted puppy coat colors and patterns, each with its probability and a plain-language explanation of the genetics behind it. This is the same process a breeder would do by hand for a single locus, extended across every locus at once — which is why a dedicated tool like What's the FURcast? is so valuable for planning a litter.

A visible coat color only tells part of the genetic story. Two black dogs can carry hidden recessive alleles for liver, dilution or recessive red, and those alleles only surface when two carriers are bred together. DNA testing reveals the full genotype at each locus, turning a guess into a calculation. The more loci you have tested for both parents, the more precise the predicted distribution of puppy coat colors becomes — and the fewer “surprise” colors appear in the whelping box.

For loci that have not been tested, a good predictor marks the trait as unknown rather than assuming a negative result, so you are never given a false sense of certainty. Combined with an understanding of the dominance relationships and epistatic interactions described in this guide, DNA-tested genotypes let a breeder plan matings that reliably produce — or avoid — specific coat colors and patterns, while still respecting the natural variability of every litter.