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.
Alleles
B: Black pigment (dominant)
Normal black eumelanin. Dominant — one copy keeps pigment black. B/B dogs are clear; B/b dogs look black but carry a hidden chocolate allele.
b: Brown pigment (recessive)
Several sub-variants exist (bc, bd, bs, be). Two copies — any combination of any two b variants — convert all black eumelanin to chocolate/liver: coat, nose, paw pads, eye rims, and eye color (often amber). One copy alone produces no visible brown.
What the B locus does
TYRP1 modifies the molecular structure of black eumelanin pigment granules. With two recessive b copies (b/b), the enzyme is non-functional, and every eumelanin-containing area of the dog — coat, nose, paw pads, eye rims, and even the visible iris — shifts from black to warm brown.
Multiple b variants exist (bc in Labradors, bd in Sloughis, bs in dogs with certain haplotypes, be in others). Crucially, any two b copies — even two different variants — combine to produce a brown dog. A dog that is bc/bd is just as chocolate as a bc/bc dog.
Important details about B locus expression
The B locus only affects eumelanin (the black pigment family). It has no visible effect on phaeomelanin (red, cream, gold). An e/e recessive red dog can be b/b — and the coat still looks entirely red or cream — but the nose will be brown/liver instead of black. This is the classic 'red Poodle with a liver nose' that hints at the hidden b/b genotype.
Chocolate dogs have lighter amber or hazel eyes compared to the brown eyes of black-pigmented dogs, because the iris also contains eumelanin that is shifted to chocolate.
Responsible breeding for chocolate means health testing first — never chasing color at the expense of soundness. Chocolate is beautiful, but both parents must be DNA tested to plan chocolate pairings reliably.
Chocolate in toy breeds we work with
Toy Poodles: Chocolate Toy Poodles are b/b. Because many Poodle lines carry b as a hidden carrier allele, chocolate can appear even from two non-chocolate parents if both are B/b. DNA testing every breeding dog eliminates the guesswork.
French Bulldogs: Chocolate Frenchies are b/b. They often also carry dilute (d/d) to produce lilac/isabella, or dilute alone to produce lilac. 'Testable chocolate' is a term used for b/b French Bulldogs specifically, distinguishing them from 'non-testable' or so-called 'cocoa' (a separate, breed-specific allele).
Cavapoos and Cockapoos: Chocolate Cavapoos and Cockapoos are b/b. Cavalier King Charles Spaniels and Cocker Spaniels both commonly carry b, so Cavapoo and Cockapoo lines frequently include chocolate carriers and chocolate dogs.
B Locus FAQ
What makes a dog chocolate or liver colored?
Chocolate (liver) happens when a dog is b/b at the B locus (TYRP1). Two recessive brown copies convert all black-based eumelanin to brown — in the coat, nose, paw pads, and eye rims. The dog is identified by its warm brown coat and brown (not black) nose. Two copies of b are required; one copy (B/b) produces no visible brown.
Can a red or cream dog be chocolate?
Yes. An e/e red dog can be b/b (chocolate) and still look red or cream in the coat — because the B locus only affects eumelanin, and e/e dogs produce no eumelanin in coat hairs. The clue is the nose: an e/e b/b dog has a brown/liver nose instead of a black one. DNA testing is the only certain way to know a red dog's B locus genotype.
Can two black dogs produce a chocolate puppy?
Yes, if both black parents are chocolate carriers (B/b). Two B/b parents have a 25% chance of producing a b/b chocolate puppy. Because B/b and B/B dogs look identical, carrier status can only be confirmed by DNA testing. This is one of the most common 'surprise' results in dog breeding programs.
What is a 'testable chocolate' French Bulldog?
In French Bulldogs, 'testable chocolate' refers to b/b at the TYRP1 (B) locus — detectable by standard canine DNA tests. This distinguishes it from 'cocoa' or 'non-testable chocolate' (sometimes called Frenchie chocolate), which is caused by a separate breed-specific mutation in another gene that some older tests didn't screen. Modern comprehensive panels (like Embark) test for both variants.
What are the b locus variants (bc, bd, bs, be)?
There are multiple recessive brown alleles at the B locus, caused by different mutations in the TYRP1 gene. The major ones are bc (common in Labradors and many breeds), bd (found in some sighthounds), bs (in some breeds), and be (in others). For practical purposes, any two b alleles — regardless of sub-variant — together produce a chocolate/liver dog. Embark and similar DNA tests screen for the common variants.
How do I breed chocolate puppies reliably?
The only reliable method is to DNA test both parents. Pair two b/b parents for 100% chocolate offspring. Pair a b/b parent with a B/b carrier for 50% chocolate, 50% carrier. Two B/b carriers give 25% chocolate, 50% carrier, 25% clear. Two clear (B/B) parents cannot produce chocolate. Without testing, you are guessing — and many breeders are consistently surprised when 'black' dogs produce chocolate.
What color are a chocolate dog's eyes?
Chocolate dogs typically have amber, hazel, or lighter brown eyes (rather than dark brown) because the iris also contains eumelanin that is shifted to the b/b chocolate form. This lighter eye is one of the visual hallmarks of a chocolate dog, along with the brown nose and brown paw pads and eye rims.
Does chocolate affect health in dogs?
The b/b genotype itself does not cause any health condition — chocolate is cosmetic. However, responsible chocolate breeding requires health testing for conditions that may be more prevalent in certain lines that also happen to have high b allele frequency. Never breed for color at the expense of health testing.