Why do Calico cats tend to be female?

Why do Calico cats tend to be female?
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People are often surprised to hear that calico cats are primarily female. This may be because calico is mistaken for a breed, when it’s actually a tri-color coat pattern of black, white, and orange.

Feline coat color is genetically linked to gender. Like humans, female cats have two x chromosomes, while males have one x and one y.

The x chromosomes are responsible for the black and orange colors in a cat’s coat—white is on a separate gene. Since male cats have only one x chromosome, they can be either black or orange, but not both. Females, however, can display both colors—one on each of their two x chromosomes.

If a male cat is calico, he has the rare x-x-y syndrome, and is probably sterile.

– Dr. Larry McDaniel, DVM for the “Purina® Animal Instincts” Podcast Series