Dominant Black (K^B)

The dominant allele at the K-Locus (K^B) inhibits the production of phaeomelanin and causes a solid eumelanin-pigmented phenotype in dogs that is commonly called dominant black. Here we look at the variations and genetics of dominant black coat in dogs.

What is Dominant Black?

The K^B allele at the K-Locus promotes eumelanin synthesis and blocks phaeomelanin expression. Whatever pattern a dog has on its A-Locus (clear sable, shaded sable , agouti, saddle pattern, tan point, recessive black) will not be visible.

Example: Did you know that the majority of Labrador Retrievers has a tan point genotype (a^t/-) but can’t express tan markings because all black and brown Labs are almost always K^B/ K^B[2]?

If a dog is able to produce eumelanin the K^B allele causes a solid eumelanin-pigmented coat in all pigmented areas. By the way, dominant black was named after the black eumelanin pigment color in a wild-type coat. But an affected dog can just as well be brown, blue or lilac.

Besides brown pigment and color dilution, there are many other traits like merle, domino, white spotting or greying that influence the colors and color pattern on a dominant black dog.

The K^B-Allele

The K-Locus in dogs has gained the ability to play a role in pigment type switching several thousand years ago^[4]. Different alleles at this gene locus can allow or prohibit agouti gene expression^[1].

K^Black or K^B is the dominant allele in this series and is responsible for a dominant black coat while k^br and k^y allow for agouti gene expression.

Since K^B is a dominant trait even one copy of K^B is enough to produce a dominant black phenotype.

Dogs with an K^B/- genotype can carry brindle (K^B/k^br) or normal agouti expression (K^B/k^y). But a dog that is homozygous dominant (K^B/K^B) can only produce dominant black puppies.

Dominant black is found in many solid or solid-and-white colored dogs in breeds like Labrador Retrievers, Newfoundland, Weimaraner, Schipperke, Border Collie, Dalmatian or German Shorthaired Pointer.

At this point, we should mention that there is currently no commercial test available for the kbr allele. Since kbr has combined features from KB and ky it will show up in tests as KB/ky. So if your dog’s test comes back as K^B/k^y he might actually be K^B/k^br, k^br/k^br or k^br/k^y.

When will a dog be dominant black?

Dominant black causes a solid color in whatever shade of eumelanin a dog can produce in all pigmented areas. But first of all to express a dominant black phenotype a dog has to be able to produce eumelanin.

• K^B is not visible is in mostly white dogs. Since white spotting inhibits a dog from having pigmented coat K^B might be partially or completetly hidden “under” the white coat.

• A dominant black dog can also never be recessive red since these dogs can’t produce eumelanin.

If a dog is recessive red (ee) the K^B loses its ability to activate eumelanin production. So recessive red dogs can only ever produce phaeomelanin and dominant black simply can not be expressed.

Example: Labrador Retrievers are almost always E/- K^B/K^B and produce a solid black or brown coat. But since yellow Labradors are e/e K^B/K^B they can’t express dominant black since they can only produce yellow pigment.

Variability of Dominant Black

Many different genes can cause a variety of phenotypes on dominant black dogs.

Pigment color

Eumelanin can be black, brown, blue or lilac depending on a dog’s genotype at the B-Locus and D-Locus:

• B/- D/- causes black pigment
• b/b D/- causes brown pigment
• B/- d/d causes blue pigment
• b/b d/d causes lilac pigment

These genes determine the color of all the eumelanin on a dog’s body.

They not only turn all the eumelanin in the coat a certain color, they also influence a dog’s nose color, skin color and even eye color.

White Spotting and K^B

White spotting is caused by a partial or complete lack of pigmentation on some areas in a dog’s coat. White can mask whatever color these areas would normally have had.

Ticking or roan in white areas has the same color the coat would have had without the white markings. So on a dominant black dog all ticking will have the color of a dog’s eumelanin.

Example: Dalmatians, German Wirehaired Pointer or English Pointers are counted as basically fixed for K^B/ K^B[2]. but any color is only visible in the spots and patches while most of the coat is covered by white spotting.

Progressive Greying and K^B

The G-Locus can cause fading of eumelanin color in dominant black dogs and gives the coat an almost multi-colored quality with a color transition between hairline to hair tips.

Affected puppies are born with full pigment color but less and less color is found in the growing hair until the hair is light gray, beige or even silvery white.

Progressive Greying needs continuous-growing coats to take full effect. This is mostly visible in long-coated and furnished breeds like Bearded Collies, Poodles and some other bearded curly dogs.

Merle and K^B

Merle deletes some pigment in eumelanin-colored areas and causes a marbled pattern of pigmented, diluted or even white patches. Since Merle only has an effect on eumelanin it affects all the pigmented areas in a dominant black coat.

Breeds where K^B and Merle can appear together are bicolored Border Collies or Pyrenean Shepherd. And of course many color-bred dogs combine both of these traits so today there are also plenty of solid merle bully breeds, poodles or spaniels .

Great Danes take it one step further and can not only be black merle but also harlequin. In affected Great Danes a breed-specific mutation at the H-Locus modifies merle to express as white coat with black patches.

Domino and K^B

There are different alleles at the E-Locus (e^A, e^G and e^H) that can cause domino or grizzle patterns. To put it simply domino reduces eumelanin production. This can cause a dominant black coat to express as agouti-like or a greyish pattern.

Older studies claimed that domino possibly had no effect on K^B[3], but today we know that this is not true. But as unique and interesting a dominant black domino phenotype might seem it is also very rare.

Black Dogs: Look-Alikes and Mix-Ups

Of course there are exceptions to every rule:

• In some dominant black dogs the normally hidden agouti locus pattern becomes visible to some extent. In dogs with a sable genotype (Ay/-) at the A-Locus this is called Seal, in dogs with a tan point genotype (at/-) this is called Ghost Tan.
• Not all solid black, brown, blue or lilac dogs are dominant black. Recessive black also only allows for eumelanin production and basically causes the same phenotype but for different reasons. Examples for recessive black dogs are black German Shepherd Dogs and bicolored Shelties.

Learn More

Links

[1] Candille SI, Kaelin CB, Cattanach BM, Yu B, Thompson DA, et al. (2007) A beta-defensin mutation causes black coat color in domestic dogs. Science 11(1): 24–30. https://doi.org/10.1126/science.1147880

[2] Dreger DL, Hooser BN, Hughes AM, Ganesan B, Donner J, Anderson H, et al. (2019). True Colors: Commercially-acquired morphological genotypes reveal hidden allele variation among dog breeds, informing both trait ancestry and breed potential. PLoS ONE 14(10): e0223995. https://doi.org/10.1371/journal.pone.0223995

[3] Dayna L. Dreger, Sheila M. Schmutz. A New Mutation in MC1R Explains a Coat Color Phenotype in 2 “Old” Breeds: Saluki and Afghan Hound. Journal of Heredity, Volume 101, Issue 5, September-October 2010, Pages 644–649, https://doi.org/10.1093/jhered/esq061

[4] Ollivier M, Tresset A, Hitte C, Petit C, Hughes S, Gillet B, et al. (2013): Evidence of Coat Color Variation Sheds New Light on Ancient Canids. PLoS ONE 8(10): e75110. https://doi.org/10.1371/journal.pone.0075110