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Cats (Felines)
Domestic Cat Breeds
Cat Behavior

Is it true that calico cats can only be female?


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April 12, 2010 9:55PM

To put it simply, calico cats are caused by the random conversion during embyronic development of X chromosomes into Barr bodies. When you have a female cat, you have two X chromosomes (XX). When the female cat embryo is a morula (earliest recognizable embryo), each cell in the embryo randomly inactivates one X chromosome and passes this inactivation onto daughter cells in the same line. This is what allows for the spotted appearance of calico cats, as we are assuming momma kitty and papa kitty had different coat colors transferred to the embryo through the X chromosome. This random inactivation is also why females are typically not color blind. Color blindness is caused by an inability to perceive certain colors due to a deficient protein that has its DNA inside the X chromosome. Females have two X chromosomes, and one of them is randomly selected to be used in the development of each focal area of the eye. If the female had a color blind father, this means each eye would be roughly half color blind, and since half is enough to perceive color well, unaffected. A female could indeed be color blind if she received "bad genes" from her mother as well, but it's a much rarer circumstance.

You do not see the calico patterns with a normal male (XY) cat because the X chromosome does not become inactivated in male animals. However, cats are susceptible to the same genetic disease we are. In one particular disease, two cells fail to separate their X chromosomes during Meiosis (an event called Nondisjunction). This cat hence receives two X chromosomes from mom, and say in the case of a male, a Y from dad. This cat's resultant genotype is XXY and the cat has Klinfelter's Syndrome. The cat appears male (i.e. has a male phenotype) but he really has two X chromosomes. This tends to be why male calico cats are much rarer and are also sterile

To make things simple its very rare to have a male calico cat. And yes male calico cats are sterile. A regular female cat has XX chromosomes and a regular male cat as XY chromosomes. A male calico cat would have XXY chromosomes which in human form this would be called Klinefelter's syndrome. Which makes the male calico cat sterile.