Calico and Tortishell Cats / Discuss

Birdie2533    says:

Are calico cats all female?

Actually, they’re not. But the odds of the birth of a male calico is about 200 to one, so they’re considered pretty unusual. Calico is not a breed, it’s a description of the fur color of a cat. Calico cats are primarily white with patches of black and orange, while tortoiseshell cats are similar to calicos but with far less visible white fur.

Much like humans, cats have one pair of sex chromosomes, females XX and males XY. The gene for fur color is on the X chromosome, so to be a calico or a tortie, the cat would need two X chromosomes (XX), automatically making her a female. Occasionally, however, Nature gets a bit convoluted, and a male kitten will be born with three chromosomes (XXY). These XXY kittens can be male calicos, though because they are genetic mutations, they are invariably sterile. Some breeders have observed that male calicos and torties also exhibit female behavior, like attempting to nurse kittens.

Speaking of cat colors, have you ever noticed that most orange colored cats are male? The orange (or ginger) gene overrides all other colors. Since male cats have only one X chromosome (the one that determines color), they'll either be ginger or not. Female cats with their dual Xs must have both of them programmed for orange for them to be that color; otherwise, the genes fight each other, and the kitty ends up any variety of colors.
Posted at 8:21PM, 27 July 2006 PDT ( permalink )