Why Are Male Calico Cats So Rare?

An extremely rare cat was up for adoption at the Humane Society Silicon Valley — but his time as a rescue came to a quick end. Not surprisingly, he was adopted – and adopted quickly!.

The reason for all the excitement is that Sherman, a male cat, is a calico — a common feline color pattern — and only one out of every 3,000 calico cats is male.

“It’s like a unicorn,” explained Dr. Andrea Berger, an HSSV veterinarian. “I’ve been involved with shelters for 20 years, and I have never seen one.”

What makes male calicos so commonly uncommon? Well, it’s all up to genetics.

Sherman the cat has two X chromosomes, which is what makes his fur calico-colored. (Photo: Humane Society Silicon Valley)
Sherman the cat has two X chromosomes, which is what makes his fur calico-colored. (Photo: Humane Society Silicon Valley)


Coat color in cats is typically a sex-linked trait, which means the physical characteristic is related to the cat’s gender.

Both male and female cats may be orange or black because the gene that controls orange fur color is on the X chromosome.

However, in males, an orange color is usually present in a striped or tabby pattern.

Female cats, on the other hand, may be tabby, calico or tortoiseshell. Calico and tortoiseshell are very similar, but calicos have patches of white, orange and brown or black while torties’ coats are strictly orange and black.

Because the X chromosome is responsible for both orange and black fur, female cats may display both colors because they have two X chromosomes. Males, however, having only one X chromosome, may be either orange or black.

For a male cat to have a calico pattern, the feline must have three sex chromosomes: two Xs and a Y.

This XXY combination can sometimes occur when there’s an incomplete division of the male’s XY chromosome pair at the time of fertilization — and it doesn’t just happen in cats. It can occur in people too, resulting in a genetic disorder known as Klinefelter syndrome.

While you might assume that a cat like Sherman is valuable because of his rarity, male calicos are of very little interest to breeders because they’re usually born sterile.

It is estimated that only one out of 10,000 male calicos are fertile.

To learn more about the genetics of calico cats, the University of Miami breaks it all down right here.


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