The Dominant Black Gene
Black is the “default” eumelanin colour for dogs. A dog which isn’t homozygous for liver (bb) or for dilution (dd) will have black eumelanin. This means that it will have a black nose and, usually, brown eyes (eumelanin affects eye colour too), and any eumelanin in its coat will be black. Eumelanin, in case you missed out the introduction pages, is one of two types of pigment that occur in dogs. The other is phaeomelanin, which doesn’t affect the eyes or nose and is only visible in the coat. It produces the colour “red”, which is anything from deep Irish Setter red to light cream. Phaeomelanin doesn’t “naturally” occur in the coat – it only appears if the dog has genes which allow it to occur.
There are two basic choices for a dog’s markings – solid (no tan markings, just eumelanin) or non-solid (tan markings of any sort). Whether a dog has a solid eumelanin (black) coat or a coat with tan markings (caused by phaeomelanin) depends almost entirely on the K locus. K consists of three alleles:
K – dominant black (solid black, no red)
k – recessive non-black (will still have black nose pigment and may have black markings, but may also have red markings too)
kbr – brindle (we won’t deal with this here – see the brindle page for more info on this allele)
A dog with even just one K gene will be solid black. A dog with two k genes (i.e. homozygous for k) will be able to show tan markings. These tan markings are determined by another locus, A. So basically, a genotype of kk allows a dog to show whatever it has on the A locus. A Kk or KK dog may be genetically tan-pointed or sable on the A locus, but won’t be able to show those markings because of its dominant black genes. Dominant black dominates the whole of the A locus, but it can be overridden by other genes, such as liver, dilution, greying and merle. All of these will alter the way a dominant black dog looks, but the one thing they cannot do is add phaeomelanin (red) to the coat. The only way phaeomelanin can be added to the coat of a dog with the dominant black gene is through the e gene (E locus) – recessive red. This turns a dominant black dog (or indeed, any dog) into a solid red dog with black nose pigment.
This all probably sounds very confusing at this point, and if you have no background in genetics you may not understand everything. Don’t worry – we’ll deal with the genes that can affect black on different pages a bit later on. For now, all you really need to know is that Kk and KK on the K locus produce a solid black dog. A kk dog may have some black in its coat, but it won’t usually be solid black. The stuff about eumelanin and phaeomelanin is particularly confusing, but I’ve made sure to use those terms all throughout this site because if you can get a handle on them, you’ll be able to understand dog genetics easily.
Those of you who do have a background in genetics through studying other species of animal may be interested to hear that dogs are one of the only species known to have a dominant black gene. Black in most animals is recessive (there is a recessive black gene in dogs – see below – but it is fairly rare). Dominant black in dogs is caused by a gene known as “beta-defensin”, which is associated primarily with the immune system. Beta-defensin has only been proven to affect coat/pigment colour in two mammals so far – dogs and cattle.
Examples of Dominant Blacks
All of these dogs are Kk or KK on the K locus. Notice the lack of red anywhere in the coat of any of these dogs. If there is a reddish undercoat or scattered red hairs, the dog is most likely a very heavy sable (or similar) rather than a dominant black, so will actually be kk. A brownish cast on the coat may, however, be due to bronzing. Bronzing is when sunlight lightens the black hairs on a dog, and it can also be caused by dietary factors. Bronzing is generally most extensive on long-haired and curly-coated breeds.
All three dogs above are dominant blacks showing no other visible genes. Dominant black is a common colour in gundogs such as these.
This Border Collie is a dominant black with irish spotting (it has the classic pattern, so its S locus genotype is most likely sisi). Note the bronzing on the tail and ears.
All of these dogs are dominant blacks with white in the piebald or irish spotting pattern and ticking or roaning.
This Border Collie is also a dominant black with irish spotting, like the other Border Collie above, but this one has the merle gene too (Mm), which has turned its black markings into broken patches on a grey base.
Believe it or not, these three dogs are genetically dominant blacks too, even though they don’t actually have any black on them. The German Spitz is a dominant black with the liver gene (bb), which has turned its solid black coat into brown, and the Greyhound and Weimaraner have the dilution gene (dd) added on top, making them blue and isabella respectively. As these examples show, in the dog world it is possible to be black without being black!
The Recessive Black Gene
Most solid black dogs are solid black because they have the dominant black gene, but there is another type of black – recessive black. Recessive black is very rare and only occurs in a handful of breeds, including the German Shepherd Dog, Shetland Sheepdog, Schipperke and Puli. Some breeds, such as the Belgian Shepherd Dog, are thought to carry both recessive and dominant black.
Recessive black is thought to be on the A locus. It is denoted by a, and is generally put right at the bottom of the A locus because it is recessive to every other A locus gene (sable Ay, agouti aw, tan points at). This means that if a dog has just one a gene, it will not be solid black (but sable, tan-pointed, etc), as it needs two a genes for the recessive gene to work.
If you’re wondering why the dog shown above is white, it’s because Samoyeds have also been proven to have the recessive black gene. However, here it is combined with other alleles, which dilute or remove the pigment.
Recessive black is, aesthetically, no different to dominant black. The only difference is in the breeding – a solid black puppy could be born from two parents who are non-solid black if they both carry (without expressing) one copy of the recessive black gene, whereas a dominant black pup could only be born if one or both of its parents are also dominant blacks. Another important aspect of recessive black is that it is on a different locus to dominant black. This makes it the only way that a dog can still be solid black if it is kk (non-solid black) on the K locus.
Unless you’re a dog breeder, recessive black is unimportant (but it’s still quite an interesting discovery!).
Seal is currently a complete mystery. Seal colouration makes black dogs appear brownish (with the nose remaining black), varying from a slight brown cast to a shade almost as light as liver. Seal dogs are born brownish whereas bronzing develops with age.
No genetic research has so far been conducted into seal, so it is unknown how it is caused or which locus is responsible for it.
Current theories include seal being an allele on the K locus (recessive to K), an allele on the A locus, or a modifier on an unknown locus that causes the A locus to partly show through on Kk dogs.
Seal mixed breed – photo by Jamie Elvert
More Examples of Dominant Black
All of the following dogs are genetically dominant black. Hover your mouse over each photo for a description of their colour.
“Dog Coat Colour Genetics.” Dog Coat Colour Genetics. N.p., n.d. Web. 24 June 2014.