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 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.
In other words, every dog will be black unless it has genes which turn its black pigment into liver, blue or isabella, or genes which
add tan (red) markings. I don't include white markings here because technically white isn't created or controlled by pigment - it is, in fact, lack of pigment.
So when I say "solid black" I assume white markings may 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 genes:
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 gene)
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.
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. Usually only longhaired or curly-coated dogs will show bronzing, and it is generally mainly on the back and around the head.
All three dogs above are dominant blacks showing no other visible genes. The Groenendael in the middle has a little bronzing on its face and neck, making
it look slightly brown. Groenendaels in fact carry both dominant and recessive black (see below), so it's impossible to know which type this dog has.
This Border Collie is a dominant black with irish spotting (it has the classic pattern, so its S locus genotype is most likely sisi)
All of these gundogs are dominant blacks with white in the piebald pattern and ticking or roaning. The pointer is most likely an extreme white (swsw) rather than
a normal piebald, because it has no patches on its body.
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 two dogs are genetically dominant blacks too, even though they don't actually have any black on them. The Portuguese Water Dog
is a dominant black with the liver gene (bb), which has turned its solid black coat into brown, and the Weimaraner is the same but with the dilution gene (dd) added on top, making it isabella-coloured.
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, saddle markings as). 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.
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!).