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Genetic George explains the K locus in dog coat color genetics, including dominant black, brindle, ky patterns, and testing tips today.
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If coat color genetics were a nightclub, the K locus would be the security or bouncer at the velvet rope. The A locus (Agouti) might show up dressed to impress with sables, tan points, and agouti patterns… but K gets the final say on whether those patterns even make it onto the dance floor.
Charlie (my Boston Terrier) believes K stands for “King,” and Mary (my Griffon) insists it stands for “Keep it classy.” Genetics says it stands for “Keep it black (sometimes)”—and honestly, that’s not far off.
The K locus is strongly associated with a gene called CBD103, and it’s famous for driving what breeders often call dominant black. The big headline is this: The K locus can mask what would otherwise be visible patterning from the A locus.
That masking effect is exactly why K matters so much in breeding outcomes. Two dogs can carry all sorts of pattern potential underneath, but if K is set to “override,” the coat can present as solid eumelanin (black/brown/blue/etc.) with minimal pattern showing.
At the K locus, we commonly talk about three alleles that shape a huge amount of what we see in the coat:
The K locus has three main alleles: KB (dominant black), kbr (brindle), and ky (non-black).
Dominant black dogs (usually KB/ky or KB/KB) tend to be solid eumelanin across the coat, though that eumelanin can be modified by other genes into liver, blue, Isabella, and even combined with patterns like merle—but you typically won’t see true red/tan areas unless something unusual is going on (more on that in a moment).
ky/ky dogs are the “non-blacks.” They show what they have on the A locus (sable, tan points, agouti, etc.). Dogs with kbr also show their A-locus pattern, but any phaeomelanin areas can be brindled.
Also worth remembering: Most solid black coats come from KB, but recessive black can also occur via the A locus in some lines and breeds.
One of the landmark discoveries in coat-color genetics is that a mutation in beta-defensin (CBD103) is associated with black coat color in domestic dogs. This is the work that helped cement the K locus as a central switch in the color conversation.
Reference: Candille, S.I., Kaelin, C.B., Cattanach, B.M., Yu, B., Thompson, D.A., Nix, M.A., Kerns, J.A., Schmutz, S.M., Millhauser, G.L., & Barsh, G.S. (2007). A beta-defensin mutation causes black coat color in domestic dogs. Science, 318(5855), 1418–1423. doi: 10.1126/science.1147880
(Charlie heard “Science” and assumed it meant treats would be dispensed. Sadly, no.)
Now let’s talk about one of the most intriguing coat phenomena breeders see in real life: seal.
Seal is currently a mystery. It’s a color effect that makes black dogs appear brownish—sometimes just a faint warm cast, sometimes almost as light as liver—while the nose remains black. Often there’s a black stripe down the back, and the legs and tail stay darker than the body.
Seal dogs are often born looking brownish, and the bronzing effect can change with age. The key point breeders can anchor on is this: a black seal will always have a black nose, no matter how “brown” the coat appears.
Here’s the frustrating (and fascinating) truth: No definitive genetic research has yet pinned down seal, so it’s unknown which locus is responsible or how it’s caused. Many seal dogs test as KB/ky and are often Ay/Ay on the A locus, which makes it plausible that the A locus is “leaking through” the black coat in some way. The mechanism, however, remains unknown—and that’s where the mystery stays.
Seal can also combine with other alleles, leading to outcomes like liver/blue/Isabella seal, and even seal merle in some combinations. Add “ghost tan” into the mix (where tan point patterning seems to whisper through dominant black), and you can see why K locus conversations rarely stay simple for long.
Mary’s summary: “So, it’s black… but also not black… but the nose tells the truth.” Mary is, annoyingly, correct.
A practical note for breeders who rely on DNA results: kbr can sometimes be defined as a combination of KB + ky signals in classic testing frameworks. That means the typical detection of KB and ky variants can leave ambiguity when kbr is present.
In other words, dogs with a KB/ky reading on a basic test may, depending on the assay, need additional analysis to correctly distinguish between possible genotypes—such as KB/ky, KB/kbr, kbr/kbr, and kbr/ky—and therefore to make a correct statement about inheritance risk for brindle versus dominant black.
The takeaway is simple: the “right” test approach can depend on breed context and what color outcomes you’re trying to predict, and sometimes a combination of methods is the most accurate path.
Understanding K doesn’t just help you predict “what color shows up.” It helps you interpret surprises, explain outcomes to puppy buyers clearly, and plan matings with fewer unintended results.
If you’re aiming for reliable A-locus pattern expression, knowing whether your dogs are ky/ky (versus carrying KB) can be the difference between “planned pattern” and “solid coat takeover.”
To celebrate K month, I’m doing a simple giveaway for one lucky SHOWSIGHT reader:
Prize: A Canine Coat Color DNA panel (or equivalent coat-color genotype assessment) to help you confirm your dog’s K locus status and better understand what may be hiding beneath the coat.
How to enter (quick and painless): Email (george@orivet.com) in (1) your breed, (2) your dog’s registered name, and (3) a clear photo of the dog standing in natural light—plus the words “K Locus Giveaway” in the subject line.
I’ll pick one winner and share a short, educational breakdown of the result in next month’s column (with identifying details removed unless you want the bragging rights).
Charlie wants the winner to also receive a snack hamper. Procurement has declined.
K locus genetics is one of the most useful tools in the coat-color toolbox because it influences what patterns can show and when. But it’s still just one chapter in responsible breeding—alongside health, temperament, structure, and long-term breed welfare.
And if you ever feel overwhelmed by the alphabet soup of loci… don’t worry. Even Charlie gets confused when Mary starts running the household agenda.
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