Cat coat genetics
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The genetics of cat coat length and coloration is a complex subject, and many different genes are involved.
The genes involved include:
- the tabby gene, T/Ta/tb, which sets the basic pattern of stripes that underlies the coat: the basic wild-type tabby gene, T, produces what is called a mackerel striped tabby; a dominant mutant, Ta, produces an Abyssinian tabby, while a recessive mutant, tb, produces a blotched or classic tabby pattern.
- the agouti gene, A. The dominant A causes banded agouti-colored hair between the usual tabby stripes, while the recessive non-agouti, a, causes non-banded hair to be an identical color as the tabby stripes, and therefore a uniform coat color.
- the white Spotting gene, S, which has variable expression, so that an SS cat has more white patches than an Ss cat. It is this gene that creates the familiar white blaze across the face, a white bib, or dappled paws.
- the White masking gene, W. It is dominant and masks all other colors. A cat that is WW or Ww will be white, no matter what other color genes it has. A cat that is homozygous recessive (ww) will express the fur colors of the Orange gene.
- The Orange gene, O, determines if there will be orange fur. In its dominant form, O, the fur will be orange. In its recessive form, o, the fur will be a shade of black, based on the B gene.
- The B gene in its dominant form, B, will produce a black color; other, recessive variants are b, producing brown (or chocolate), and b1 producing light brown or cinnamon.
- the Dense pigment gene, D, corresponding to the dilute gene, d. When a cat has two of the recessive d genes, black fur becomes blue, and orange fur becomes cream. Blue-cream cats are normally female only, for reasons similar to the calico or tortoiseshell colorations.
- the Inhibited pigment gene, I, that produces tipped hairs that are pale but colored at the tip.
For a cat to be calico (or blue-cream), it must simultaneously express two alleles, O and o, which are located on the X chromosome. Males normally cannot do this, as they have only one X chromosome, and therefore only one allele, and so calico cats are normally only female.
It could be deduced that a grey male cat with a white bib and paws:
- has the o variant of the orange gene on its only X chromosome (because the grey color corresponds to black, not orange)
- has at least one S variant of the white Spotting gene (because it has the white bib and paws)
- has two w genes (because it expresses a fur color)
- has the dominant B gene (because its fur color is a shade of black rather than brown)
- has two d (dilute) genes (because its fur is grey, rather than black)
Cat fur length is governed by the Long hair gene in which the dominant form, L codes for short hair, and the recessive l codes for long hair.
There is also a gene for hairlessness, which produces the Sphynx cat.