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They're the result of an exceedingly rare genetic abnormality.
By
Laura Moss
Laura Moss
Writer
- University of South Carolina
Laura Moss is a journalist with more than 15 years of experience writing about science, nature, culture, and the environment.
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Updated July 18, 2022
Male calicos are the unicorns of the cat world. Only females carry the chromosomal combination needed for the calico pattern, but every now and then, a male cat will develop an extra chromosome and come out with the signature tricolored coat. The chances of this happening are only about one in 3,000.
These uncommon felines are coveted by buyers, but unpopular among breeders. Find about more about calico cats and why male calicos are so rare.
What Is a Calico Cat?
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"Calico" describes not a particular breed of cat, but rather a certain pattern of cat including any three colors—white, cream, and grey, or the more widely recognized white, orange, and black combination. This coveted color scheme can show up in a number of cat breeds: American shorthair, British shorthair, Manx, Japanese bobtail, Maine coon, Persian, and more. Being calico doesn't affect the cat's personality or lifespan, although males tend to live fewer years than females due to the chromosomal differences discussed below.
What Makes Male Calicos So Uncommon?
Genetics are the reason calico tomcats are so rare. Coat color in cats is typically a sex-linked trait—in other words, color is coded into certain chromosomes. Both male and female cats can be orange (a mutant gene) or black because the gene that controls those colors is on the X chromosome. And while females can have both colors, because they have two X chromosomes, males, who have one X and one Y chromosome, can only have one or the other unless they have a genetic abnormality. In that case, three chromosomes—including two Xs—are present.
An article by the American Council on Science and Health explains how the gene that dictates fur color is located on the X chromosome, hence the unusual pattern:
"If the X chromosome carrying the gene for black fur gets inactivated, that cell will instead create orange fur. If the X chromosome carrying the gene for orange fur is inactivated, that cell will create black fur.Because the Xs that are inactivated are chosen at random, the patternon each calico cat is distinct from another."
This is why the vast majority of calico, tortoiseshell, and tabby cats are female. The difference between these three is that calico cats have large, distinctive markings on white fur, while tortoiseshell cats have mottled tricolor coats, and tabby cats are streaked, with M-shaped markings on their foreheads. Generally, tortoiseshell cats (aka torties) have very little white, and if they do it appears on the face, paws, or chest. They tend to have two colors (marbled orange and black), whereas calicos have three. Tabbies can be identified by stripes on their sides and typical black and ginger patches.
Chromosomal Abnormalities in Male Calicos
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For a male cat to have a calico pattern, the feline has to have three sex chromosomes: two Xs and a Y. This phenomenon can happen in both humans and animals and is, in either case, known as Klinefelter syndrome. The XXY combination can occur when there's an incomplete division of the male's XY chromosome pair at the time of fertilization.
This phenomenon is rare, although the likelihood of a male cat ending up with an extra X chromosome is unclear. Klinefelter syndrome affects only one in every 500 to 1,000 humans. Like humans with this condition, cats with the XXY combination have malformed sexual organs, which typically makes them sterile. This makes them an unpopular pick for breeders, despite their rarity.
Every cat is different, but often male calico cats with Klinefelter syndrome experience a range of health problems that shorten their lifespans. Some common problems associated with the syndrome include increased body fat, which leads to diabetes, joint pain, and heart disease. One pet insurance site says, "It's possible for male Calico cats with Klinefelter’s Syndrome to lead full and happy lives, but they may require special care to help deal with these issues."
Calico Cats in Folklore
In addition to being an infinitely interesting research subject—what with the way their genetics present through their physical traits and the anomaly of the XXY variation—calicos have spawned many a myth and superstition over the years. According to Irish folklore, a calico cat's tail can cure a wart. They've been a symbol of fortune in Japan since the 19th century, hence the tricolor pattern of Maneki-neko, the beckoning feline figurine commonly displayed in shops and restaurants. In 2015, 3,000 people attended the funeral of a calico stationmaster that was thought to increase ridership at a Japanese train station.
Even outside of Japan, calico and tortoiseshell cats are referred to as "money cats" because they are thought to bring wealth and good luck to the families who adopt them. And if uncommonness is the cause of their innate good fortune, then a male calico cat like Sherman must be impossibly lucky.
Why This Matters to Treehugger
At Treehugger, we are advocates of animal welfare, including our pets and other domestic animals. The better we understand our cats, the better we can support and protect their wellbeing. We hope our readers will adopt rescue pets instead of shopping from breeders or pet stores, and will also consider supporting local animal shelters.
