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A Calico Cat Wears a Coat of Many Colors

calico cat
Calico cats, like this tiny kitten, are almost always female. And "calico" actually refers to the markings on their fur, not their breed. AlexTurton/Getty Images

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You might think of only those animals living in the wild as having distinctive coats or markings. Zebras, giraffes and tigers come to mind. But the domesticated calico cat not only wears a unique coat, this fascinating feline also has other intriguing features that make her worth knowing about. Here's a hint: Amazon.

No, not the e-commerce site, though your calico probably loves playing in the empty boxes lying around your apartment. Think more like Amazons, as in the tribe of ancient female warriors. What's that got to do with calico cats? Keep reading.

First, "calico" refers to the tricolor cat's fur. It's not a breed. Calico cats are almost always white with black and orange splotches, although they can sometimes sport other colors like brown or gray. Second, most interestingly (and here's where the Amazons come in), calicos are almost always female. It all comes down to basic genetics.

Calico Cats and Genetics

Let's do a quick biology review. Eggs have one X chromosome and are contributed by the female. Sperm is contributed by the male and contains either an X or a Y chromosome. When sperm joins with the egg, the combination of XX or XY creates the gender of the cat. The sex chromosomes are referred to as the XX (female) or XY chromosomes (male). Some attributes, like coat color, are passed down in the cat's sex chromosomes, says Dr. Bruce Kornreich, associate director of the Cornell Feline Health Center at Cornell University in New York.

"Normal females are XX and normal males are XY," Kornreich says. "Because females have XX, they can receive coat input from the queens (females) and the toms (males). In other words, if one of the X chromosomes (in a female cat) carries a black gene and the other one is an orange gene, in that case you'll have this (calico) mix. But because males only get one X chromosome, it's not common for them to have this mix. They only get the coat color from the queen alone, from one parent."

Think of it this way: In order for calico to occur, one of a cat's X chromosomes has to carry a black gene and the other might carry an orange gene. If both the female chromosomes are black, then she'll be black. If they're both orange, she'll be orange. If the chromosomes are mixed, black and orange, she'll be calico.

The patches in calicos occur during the early stages of development in a complicated process called "X chromosome inactivation," which happens when genes for black fur and genes for orange fur are randomly distributed all over the fertilized egg. A black patch of fur is created when the X chromosome carrying the gene for orange fur is inactivated. Conversely, an orange patch of fur is created when the X chromosome carrying the gene for black fur is inactivated. Because of this unusual genetic component, no two calico cats are alike. The markings will never be exactly the same, even in twins.

Male Calico Cats Are Rare

Something else highly unlikely in calico cats? Males. The chances are only one in 3,000, Kornreich says. So, what accounts for that random one out of 3,000? Occasionally a male cat will inherit an additional sex chromosome and becomes XXY.

"There's actually something similar in humans called Klinefelter syndrome," Kornreich says. "But in the case of the cat, it will have an extra chromosome and if both the Xs aren't the same coat color, they can become calico. It's very rare, as the one in 3,000 number suggests, but it does occur."

If being rare wasn't enough of a life hurdle, male calicos are also sterile. And even though they can't reproduce, experts still recommend they be neutered to deal with territorial spraying or other behavioral issues.

Are Calicos Cool Pets?

As for whether calicos make good house pets, cats in general have a reputation for being aloof or standoffish. Kornreich says there is good science to back up the notion that behavior can be genetically imparted, but that has to do with breeding and calico is all about coloring. Is there any connection between the color of a cat's coat and its behavior? A 2015 study by researchers at the University of California-Davis explored that very idea.

Dr. Liz Stelow, a behavioral expert at UC-Davis Veterinary Medical Teaching Hospital, and her colleagues, professors Melissa Bain and Phillip Kass, used an internet-based survey to collect data from more than 1,200 "cat guardians." The survey asked these pet owners to rate the frequency of behaviors such as hissing and biting using a five-point scale.

"Guardians reported sex-linked orange female (tortoiseshells, calicos and "torbies") black-and-white, and gray-and-white cats to be more frequently aggressive toward humans in three settings: during everyday interactions, during handling, and during veterinary visits," read the report.

Does that mean calicos don't make good pets? Not necessarily, says Kornreich, describing the study as anecdotal. "It's based on an owner's perceptions," he says. "The notion of calico cats being more aggressive, picky or finicky has always been folklore."

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