The science behind why calico cats are female

With their patches of multicolor fur, usually in white, orange, and black, calico cats’ markings are unique. Except for in cases of genetic mutations, the calico pattern solely occurs in female cats, according to the article “A Calico Cat Wears a Coat of Many Colors” by Patty Rasmussen. A close examination of the genetics behind cat fur provides a thorough explanation for why these markings are generally found only in female cats.

The genetics behind a cat’s coat

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According to the article “The Genetics of Calico Cats,” several genes are responsible for a cat’s fur color, including one on the X chromosome. Females receive two X chromosomes, one from the mother and one from the father. Barring genetic mutations, a male will receive one X chromosome from the mother and a Y chromosome from the father. Thus, a male cat will only get a gene for fur color from its mother, while a female cat will get a gene for fur color from each parent. Different cells in the female will express this differently, as each cell will inactivate one of its X chromosomes.

The genetics of calico cats

Source: Shutterstock

Let’s say we have two cats, an orange female cat, and a black male cat. When these two cats procreate, their genes for fur color can manifest in their offspring in a few different ways, as outlined by both Rasmussen’s article and “The Genetics of Calico Cats.”

1. Male kittens with XY chromosomes will receive the gene for orange fur in the X chromosome from their mother. Since they receive a Y chromosome from their father and the gene for fur color is not linked to the Y chromosome, their coat color will not be affected by his genes.
2. Female kittens will receive a gene for orange fur from their mother and a gene for black fur from their father. Because each cell will have one X-chromosome inactivated, different parts of the cat’s coat will be orange while others will be black. If the fur also has patches of white, or unpigmented fur, known as piebalding, the female cat will have the markings of a calico cat.
3. In cases of genetic mutations, male cats can end up with two X chromosomes and one Y chromosome. When this happens, the male kittens can also have a fur with a calico pattern.

Calico cats are not only interesting for their distinctive markings but also for the fascinating genetics that makes them who they are.