If you're writing a soap-opera script about cats, leave out storylines that involve calico kittens accidentally switched at birth. Random gene expression practically ensures no pair of three-color cats looks identical. There qre multiple terms for specific coat configurations but "reverse calico" is a misnomer without a precise meaning.
Cat Color Genetics
If you want to understand why the term "reverse calico" doesn't make much sense, you need to learn a little bit about cat genetics. Cats carry hair color genes for orange or black fur on their X chromosome. This is straightforward in male cats -- they get orange or black fur -- but female cats can get both genes. Orange is dominant, but a process called lyonization randomly mutes one of the X chromosomes in each cell. Black and orange cats are called torties, short for tortoiseshells.
Calico cats are tortoiseshells with white fur caused by a different gene. (Say "pigmentless fur" and "piebalding" if you want to sound like a scientist.) Tortoiseshells have mixed swirls of orange and black fur. Many appear as if their dominant color is black, so some people call orange-dominant tortoiseshells "reverse torties." The term isn't popular today, and its accuracy is questionable. Calicos generally have solid orange and black patches and their stomachs and paws are often solid white. Neither black nor orange coloring appears dominant among all calicos, so there's no trend to reverse. That's why there's no such thing as a "reverse calico." You could assume so-called reverse calicos have more black spots than orange spots, a la reverse torties, but that usage isn't common, and its accuracy, too, is questionable.
The Cat's Pajamas
The name calico refer to all three-color cats, not a breed. Domestic short-haired cats -- the mutts of the cat world -- represent the bulk of calico cats. Some fanciers accept the tri-coloring as an unusual variation in Persian and Manx cats, among others, though. Cats come in eight basic colors, six of which -- gray, dark brown, tan, medium brown, beige and cream -- result from variations on black and orange genes. Calicos with these diluted colors are sometimes called "dilute calicos" or are named after the particular shade, like "blue calico" for gray, white and orange variations. The same goes for torties.
Almost all calicos (and, by extension, tortoiseshells) are girls. It's possible to have a male calico, but they're quite rare. Such cats are XXY, not XY, so, technically speaking, they're hermaphrodites. A lot of people still refer to them as "male calicos," though. These cats are usually sterile and have Klinefelter syndrome, which can greatly shorten their lives. An even rarer variety is a chimeric cat, who has both XX and XY cells in his body. They could, theoretically, be fertile, although they're vanishingly few well-documented studies.
- University of Miami Department of Biology: The Genetics of Calico Cats
- University of Maryland Chemical and Life Sciences Graduate Program: Mitosis, Meiosis and Calico Cats
- University of Florida: Genetic Control of Coloration in Cats
- TheCatSite.com: Calico Cats
- R. Roger Berreton and Nancy J. Creek: Cats of a Different Color
- University of California, Berkely: Basic Genetics as Revealed by Cats
- MessyBeast.com: Tortoiseshell and Tri-Color Cats
- Featherland Cattery: The Pigment Parade
- Fanciers.com: Cat Color FAQ -- Common Cat Colors
- Wendy Christensen: Calico Genetics
- Catster.com: Domestic Short-Haired Cats
- National Geographic: Domestic Cat (Felis Catus)
- UC Davis Veterinary Medicine: Feline Coat Color Tests
- J. Wastlhuber: History of Domestic Cats and Cat Breeds
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- Nature.com: X Chromosome -- X Inactivation
- TheCatSite.com: A Reverse Dilute Calico?
- TortoiseshellCat.org: All About Tortoiseshell Cats
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- TheCatSite.com: Calico Cats
- Thinkstock Images/Comstock/Getty Images