Sandwalk on Calico Cats

Male cats can be black and white or orange and white, and so can female cats; but with the normal number of chromosomes, only female cats are black and orange and white, or “calico.” The reason is that the colour gene for black or orange is on the X chromosome. Males have only one to express. Females are expressing sometimes the X chromosome from their mother and sometimes the X from their father, and thus expressing different colours. The white is caused by another gene that suppresses colour, and can be expressed on more or less of the cat’s hide.

Dilute calico (Peek-A-Boo)

There’s been a discussion on Talk.Origins about calico cats—do they have to be female? The color pattern is an interesting combination of sex-linked genetics and epigenetics. Epigenetics is the inheritance of characteristics other than nuleotide sequence. In this case, it’s inheritance of an inactivated X-chromosome

Go to Larry Moran’s Sandwalk: Calico Cats for a detailed explanation.

The tortoiseshell cat has more blended colours than the calico, but the same sex-linked rules apply. This image from Kittenwars.com is called “Oswald and his sisters.” You can tell which kitten is Oswald because three of the kittens mix orange and black, while one has only black fur—so he’s the male.

I had a long-haired, tortoiseshell cat given to me when she was thirteen years old. She lived for ten more years, making her the oldest cat in my veterinarian’s practice.