Dog coat color calculator

How is dog coat color inherited?

Every color a dog can have comes from just two pigments: eumelanin, which is black or brown, and phaeomelanin, which is red or yellow. A handful of genes decide which pigment is made, where on the body and in what shade. Each gene sits at a spot called a locus, and every dog has two copies of it, one from each parent. A puppy gets one copy from the sire and one from the dam, picked at random, which is exactly what a Punnett square shows.

Worked example: two black Labradors that both carry yellow (E/e) and chocolate (B/b). The calculator opens with this pair. Per puppy, the odds are 56.25% black, 18.75% chocolate, 18.75% yellow with a black nose and 6.25% yellow with a liver nose. In a litter of eight you might get exactly that 9:3:3:1 split, or all black: each puppy is a separate roll of the dice.

The six loci in the calculator

The A locus uses the classic four alleles. UC Davis now reports it in more detail: ay splits into dominant yellow and shaded yellow, and at into black saddle and black back. If your test uses the new names, pick the classic allele they belong to.

Which gene wins? The order that decides color

Genes don't act side by side; some override others. The calculator applies them in this order:

1. E locus first. A dog with two copies of e can't put black or brown pigment in its coat, so it is red, yellow or cream whatever the other genes say. Its nose still shows black, liver or a diluted shade.
2. K locus next. One copy of KB (dominant black) makes the coat solid and hides the A locus completely. kbr adds brindle stripes to the red parts of the pattern. Only ky/ky dogs show their A pattern as it is.
3. A locus pattern. Fawn or sable, agouti, tan points or recessive black (a/a), which looks solid even without KB. Em adds a dark mask that shows on the lighter patterns.
4. B and D change the shade. Two copies of b turn black into brown (liver, chocolate), as the UC Davis brown test explains; two copies of d dilute black to blue and brown to lilac, per the dilute test.
5. M adds merle on top, as patches of diluted black or brown pigment.

Why you should never breed merle to merle

Merle is incompletely dominant: one copy (M/m) gives the familiar marbled coat, two copies (M/M) give a double merle. Breed two merles and 25% of puppies are expected to be double merles, with another 50% merle. Double merles are often largely white, and UC Davis lists hearing and eye defects, along with skeletal, heart and reproductive problems, among the risks. Breeding two merles is discouraged.

Pairing a merle with a non-merle avoids double merles entirely: 50% of puppies are merle and the rest are not. The catch is proving the other parent is really non-merle. Cryptic merles carry a short form of the gene and show little or no pattern, and a red or yellow (e/e) dog can carry merle without any visible sign. A merle DNA test on both parents is the only safe check, and the calculator warns you whenever one parent's merle status is a guess.

What if the parents aren't DNA tested?

You can still use the calculator by picking a "Not tested" option that matches what you see, such as "Not tested: black nose" for the B locus. Each of those treats every genotype that fits the description as equally likely, so an untested black-nosed dog counts as a 50% chance of carrying brown. That is a planning assumption, not a fact about your dog: in a breed where brown is rare, the true chance is much lower.

Visible colors tell you more than you might think. A brindle dog must have kbr, a blue dog must be d/d, and a tan-pointed dog with no brindle must be ky/ky with at least one at. Start with what is certain and use "can't tell" only where a gene is hidden, such as the A locus under a solid black coat.

What the calculator can't predict

• White markings. Piebald and other white spotting, ticking and roan depend on further genes and are not modelled.
• Shade of red. Whether a red dog is cream, gold or deep red depends on intensity genes outside the six loci.
• Breed-specific variants such as cocoa in French Bulldogs, harlequin in Great Danes, grizzle in Salukis, and dilutes that UC Davis notes are still unexplained in some breeds.
• Merle length. Testing labs such as UC Davis now report merle by allele size, which predicts how strong the pattern is. The calculator treats every merle allele the same.
• Brindle tests. The UC Davis K-locus test reports dominant black (KB) only, so brindle carriers are usually worked out from the dog's coat and pedigree.