Last year I told you about seven genes that control almost all cat fur colors and patterns. Of course, I couldn’t get to some of the more fascinating and complex color patterns such as the pointed color of Siamese and other Oriental breeds, the smoke and shaded colors, the "hairless" gene, the rex (curly/wavy fur) gene, rosette patterns, and rare colors such as brown. So, let’s get started with lesson two on cat genetics and unusual coat patterns and colors.
Brown cats are rarer than you might think; in fact, the Havana Brown is one of the very few breeds that do produce a true brown coat. Brown isn’t just a faded black; it’s controlled by a gene all its own, a mutation of the B gene that produces black pigment. There are two shades of brown: chocolate (b) and cinnamon (b1). Solid brown cats also carry the non-agouti gene, a.
The colored points of Siamese, Balinese and Himalayan cats are due to a phenomenon called partial albinism. The recessive gene cs causes temperature-sensitive expression of color pigments: on the warmer parts of the cat’s body, the fur is paler, but on the cooler parts of the body such as the ears, face, tail and legs, the color is darker. The most common colors are seal (black/dark brown) and chocolate (brown). Other colors such as lilac and blue occur because of a dilution gene related to the dilute color gene, d.
If you’ve ever seen a cat with a shaded silver coat, you were probably amazed by its beauty — and if you were like me, you wanted to know what genes made that happen. Well, it’s all about the inhibited pigment gene, I. The dominant allele, I, produces hairs that are colored at the tips and white at the base. This gene also interacts with the non-agouti gene, a, to produce the smoke color pattern.
Rosettes are the "leopard spots" seen in some hybrid breeds, such as the Bengal. There’s a lot of speculation about what genes might be responsible for rosettes, and at this time the most commonly accepted hypothesis is that they’re a variant of the agouti gene, A, which causes tabby patterns.
If you’ve ever petted a Sphynx or Peterbald cat, you know they’re actually not hairless at all; they have very fine hair that feels like peach fuzz. But what gene controls this odd mutation? Surprise — it depends on the breed! Variations of the recessive h gene control hairlessness in the Canadian, British and French versions of the Sphynx, but in the Russian-born Peterbald and Donskoy breeds, hairlessness results from a variant of the dominant gene, H.
As with all fur colors and patterns that don’t occur in nature, the rex coat popped up as a spontaneous mutation in a number of different locations around the world. Thus, like the hairless gene, there are different variations of it. Variants of the recessive r gene control the coats of the Cornish Rex and Devonshire Rex. The dominant Se gene controls the coat of the Selkirk Rex, and it’s thought that a special allele, the dominant Lp, produces the LaPerm‘s unique curly fur.
Keep in mind that no gene acts in isolation. There are hundreds if not thousands of genes that control every element of your cat’s coat color, length and texture. This is an extremely basic explanation of a very complex and fascinating subject. If you’d like me to go into more depth about these or any other cat genetics, let me know in the comments.
One final note: A lot of you asked about the genetics that control orange, calico and tortoiseshell patterns. I actually interviewed a genetics teacher about this on my blog, so if you want to get the full scoop on marmalade kitties, check out this post.
About JaneA Kelley: Punk-rock cat mom, science nerd, animal shelter volunteer, and all-around geek with a passion for bad puns, intelligent conversation, and role-play adventure games. She gratefully and gracefully accepts her status as chief cat slave for her family of feline bloggers, who have been writing their cat advice column, Paws and Effect, since 2003. JaneA dreams of making a great living out of her love for cats.