I’ve been thinking about how cats get their markings. My brother once told me someone told him it has something to do with temperature. That always stuck with me, but…the temperature of what, exactly? I pictured a tangle of kitten fetuses squished up against each other in utero. I imagined different splotches of color spreading across swaths of their fur depending on how and where each one was snuggled up against another. Maybe it worked sort of like a mood ring? A whimsical notion but almost certainly deeply flawed.
When I looked into the matter, I found I was pretty far afield. The temperature thing definitely doesn’t apply to feline coat markings across the boards. But it wasn’t a complete red herring. Temperature comes into play in a specific form of albinism that produces the trademark “point” coloration of Siamese cats (and their similarly patterned brethren–the Himalayans, Burmese, Tonkinese, Balinese, etc.).
There’s an enzyme, tyrosinase, whose job is to make melanin–the pigment that gives fur its color. In Siamese cats, the gene that makes tyrosinase is a clunker; the resulting enzyme doesn’t work at the regular body temperature of cats. Result: No color. But on the bits of the body that are cooler–the ears, face, tail and paws–tyrosinase behaves normally. The result is that striking contrast between the light torso and dark point areas.
And there is an in utero aspect that’s worth mentioning. Because unborn kittens in the womb are kept so uniformly toasty-warm, Siamese kittens are solid white when make their debut. Their dark points don’t start to emerge till a few weeks after birth.
Throughout their lives, temperature will continue to influence the shades of Siamese cats’ coats. If fur has to be shaved, for example for a veterinary procedure, it will commonly grow back dark. That’s because the skin temperature when “bald” is cooler, and therefore the screwed up enzyme is able to produce melanin. It’ll fade when the skin is furry again and therefore warmer. I even saw an anecdote about a cat who liked to lounge on a heat register and developed a very light patch of fur corresponding to the shape of the vent. If a Siamese cat spends a lot of time outdoors, its coat may lighten in the summer and darken in the winter. The mnemonic “cooler=color, warmer=whiter” helps me remember this intriguing relationship between temperature and pigment.
Do you have a Siamese cat? Ever notice any color shifting?
Animals Underfoot 
