In discussing small cat hair colour, I think we have to divide the world of the small cats into two groups: the purebred cats and the non-purebred cats.
Purebred cats
These are created through artificial selection a.k.a. selective breeding. Selective breeding determines the genes that the cats carry and these genes determine the coat colour and pattern. In short, the human hand is written all over the purebred cats but nature does the finessing.
Non-purebred cats
The non-purebred cats are the standard domestic cats and the small wild cat species of which there are 30.
The coat colour and pattern of the small wild cat species are entirely determined by natural selection as espoused by Charles Darwin. This process works to improve survival by allowing genetic mutations to take hold and become fixed when they improve survival.
The non-purebred domestic cats are also subject to natural selection but influenced by the fact that they are domesticated and therefore their survival is influenced (supported) dramatically by the fact that they live in the human home. That’s why they have produced coat types which are not great camouflage. And it is why the coat of the small wild cat species are always excellent camouflage to aid survival.
The domestic cat in a good home does not need camouflage. They need to look attractive for their human caregiver. I regard this as a human influenced version of natural selection.
The production of colouring and patterning
It’s a very complex process which has been studied quite extensively and there is more to learn. The control of hair colour and pattern in the small cats has been investigated by Steven O’Brien and Eduardo Eizirik at the National Cancer Institute in Fredericksburg Maryland, USA. And other geneticists.
A lot of the work has been conducted on mice because scientists believe that the control of hair colour and pattern is the same in all mammals.
Several genes control the way melanin – which is the pigment that creates colour and pattern – is deposited within the hair strand at the hair follicle through the functioning of melanocytes which are cells that produce the pigment. And these cells control how the pigment is delivered to the hair strands when they are growing for the first time.
Each hair strand has its own melanocyte at its base. And if we take the tabby coat which is controlled by the tabby gene (the agouti gene A), we can see that the melanocytes work in unison across the entire body.
RELATED: Comprehensive page on the tabby coat.
The agouti gene dictates that melanin is deposited into the hair strand in bands. One band is darker than the other. If the dark band is at the top of the hair follicle the observer sees a dark coat at that place. If a group of hair strands with a dark band at the top are clumped together in a solid circle you will see a spot on the coat. That would be the spotted tabby coat. And there is, as you probably know, the mackerel i.e. striped tabby coat and the blotched tabby coat.
In basic terms, the smoke coat which is very popular, is produced by hair strands with a dark tip and a silver strand below it which is visible. The overall effect is a smoky kind of appearance. Clearly, in this instance, the melanin producing cells deposit the pigment into the hair strand when it first emerges from the skin then they stop producing it for most of the hair strand. The tip contains melanin and the rest of the strand doesn’t.
The entire coat is like a work of art, a painting, and the artist is nature using genes to create these beautiful patterns. And in the example of the tabby coat, it is about camouflage to protect the cat and improve survival. This is the original small wild cat coat which has been inherited by the domestic cat. It still the most common but there are now many other types of domestic cat coat which are not good camouflage.
The tabby coat of the domestic cat is higher contrast than it is in the African wildcat, the ancestor of the domestic cat. It’s as if nature has hardened up the pattern, made it more beautiful to the human eye whereas the wildcat needs a pattern which is in perfect harmony with its surroundings. It’s purely functional whereas for the tabby domestic cat there is a desire to aesthetically please the human caregiver. The objectives are different. The contrast has been improved even further in the popular purebred Bengal cat that’s thanks to human intervention by breeders employing selective breeding to make their cats more attractive to purchasers.
The white coat is due to a lack of melanin being present in the hair strands which leaves the hair strand an opaque white. This is not good camouflage and is due to a genetic mutation which is maintained in the domestic cat world.
In the small wild cat world, you will very rarely see white cats. Sometimes it will be due to albinism which is a complete lack of melanin: once again due to a mutation. But the white coat can be due to either albinism or the less impactful gene that creates a white coat.
Eye colour
Eye colour is linked to coat colour because the genes that control the coat can also control the pigmentation in the iris of the eye. The classic example is the white cat with blue eyes. Blue eyes are eyes without pigmentation in the iris. The gene which removes pigmentation from the hair strands also removes pigmentation from the iris. And it goes further because it can also affect the hearing mechanism of a domestic cat rendering them deaf.
