Hear the science behind uncommon female orange tabby cats and the extremely rare tortoiseshell or calico male cat.

Question: I have heard that all orange tabby cats are male, and to find one that is female is rare and worth up to $1,000. I also have heard that calico cats and tortoiseshell cats are female and to find a male is just as rare and prized. Is there any truth to this?

Answer: Your first statement is incorrect. Most, but certainly not all, orange tabby cats are male. Orange tabby cats are about 80/20 male to female. We have many female orange tabby cats in my practice. There is no monetary value, per se, associated with a female orange tabby cat. Calico and tortoiseshell cats, however, are almost always female.

Here’s how it works. To have black and orange in the same cat, the cat needs two X chromosomes. Two X chromosomes mean the cat will be female. Male cats need a Y chromosome and are XY.

Occasionally a mutation will arise during embryonic development and a kitten will be born with an extra chromosome: XXY. The two Xs allow for the cat to be black and orange. The Y makes it a male. This is how you get a tortoiseshell or a calico male cat.

Tortoiseshell and calico male cats are uncommon (one out of 3000 are male), but don’t get your hopes up about breeding these rare cats for money. As a result of this mutation, most tortoiseshell and calico male cats are sterile.