Home Miscellaneous Why Are Calico Cats Always Female?

Why Are Calico Cats Always Female?


Calico cats have always been a rare sight to behold mostly because of the reduced numbers that have been observed in comparison to cats of various other colors. This is one of the reason for which, in many cultures, they are believed to bring good luck. For instance, in the United States, calico cats are sometimes referred to as money cats due to their coloring and rarity while in Japan, the Maneki-Neko figures depict Calico cats, bringing good luck.

What most people are not aware of is that not only are calico cats fewer in number than other cats, but there are also significantly less males than females. Actually, a calico male cat is an oddity, since the genetic chances of a calico cat being male are extremely low.


In order to understand the logic behind their genetic coding, it would first be necessary to clearly differentiate a calico cat from all the rest. The term “Calico” refers only to a color pattern on the fur, not to a breed or to cats that have eyes of two different colors. Not only that, but in order to be termed a calico, a cat must present three distinct colors on its coat. Usually, it describes the color pattern of a white cat with orange (or red or reddish-brown), and black (or grey or blue) patches on the coat.

Since “calico” is a color and not a breed, these cats may be large, small, long-haired, short-haired and even hairless, if the cat happens to be one of the breeds with any of these characteristics.
Among the breeds whose standards allow calico coloration we can count the following: the Manx, American Shorthair, British Shorthair, Persian, Japanese Bobtail, Exotic Shorthair, Siberian, Turkish Van, Turkish Angora and Norwegian Forest Cat.
This does not go to show that other cat breeds cannot produce a calico kitten. However, statistically speaking, the probability of this happening in other breeds other than the aforementioned ones is significantly lower. Taking all of this into consideration, it is no surprise that all breeders request a steeper price for any calico kitten that these breeds produce. Unless you are prepared to pay an extra amount of money do not set your sights on having a calico kitten unless she is a domesticated cat of no particular breed.

As to the reason for why most of them are female is due to genetic determination which, in this case, is linked to the X chromosome. The locus of the gene for the orange/non-orange coloring is on the X chromosome and female cats normally have two X chromosomes instead of an X and Y chromosome as males do. Each kitten gets two sex chromosomes, one from its mother and one from its father. If it has two X chromosomes then it is a girl while a kitten that has an X and a Y chromosome is a boy. Since only boys have Y chromosomes, the mother always passes on an X chromosome to its offspring while the kitten’s gender is determined by the father’s chromosome. This is similar to gender determination in humans. The other 18 pairs of chromosomes are known as autosomes.

In contrast to humans, most cats have 38 chromosomes (19 pairs). The reason that this is an interesting aspect is because some cat species in South America have only 36 chromosomes.

The cats that have 36 chromosomes are those in the Ocelot lineage. They are the Ocelot, Oncilla, Geoffroy’s Cat, Pampas Cat, Kodkod, Margay, and Andean Mountain Cat while the Andean Mountain Cat is yet to be confirmed to fit this category. So what happens when a cat with 36 chromosomes breeds with a cat who has 38? Well, you get a cat with 37 chromosomes. So there is some compatibility, but breeders consider that the males with 37 tend to be sterile.

What is even more interesting is that some cat species have an unknown number of chromosomes due to the fact that the tests have never been done. As to why tests haven’t been done on these species it is mainly because some very rare cats have barely been studied at all, let alone had a genetic analysis. The logistical difficulties of finding rare cats in remote and sometimes hostile habitats is one of the reasons for the lack of research.

Each specific trait is coded by certain portions in the DNA. They are comprised of many genes which in turn is are made up by each chromosome. Genes on a cat’s chromosomes determine the cat’s color. About 20 different genes altogether determine the color and pattern of a cat’s coat. There are only two basic fur colors: black and red. These colors are produced by different pigments and all other variations in color are variations of these two.

To be more specific, the locus of the gene for the orange/non-orange coloring is on the X chromosome and this is why most calicos are females. The alleles present in those orange loci determine whether the fur is orange or not. The coding for white is a completely separate gene. In female mammals, one of the X chromosomes is randomly deactivated (which is called “X-inactivation”) in each cell. In contrast to female cats which all have two X chromosomes, male placental mammals, including chromosomally stable male cats, have one X and one Y chromosome. And since the Y chromosome does not have any locus for the orange gene, there is no chance that an XY male could have both orange and non-orange genes together, which is what it takes to create tortoiseshell or calico coloring. Therefore, the XXY mutation is a requirement for a male cat to be a calico.

In her book Shrinking the Cat: Genetic Engineering before We Knew about Genes, Sue Hubble offers further explanation on this matter:
“The mutation that gives male cats a ginger-colored coat and females ginger, tortoiseshell, or calico coats produced a particularly telling map. The orange mutant gene is found only on the X, or female, chromosome. As with humans, female cats have paired sex chromosomes, XX, and male cats have XY sex chromosomes. The female cat, therefore, can have the orange mutant gene on one X chromosome and the gene for a black coat on the other. The piebald gene is on a different chromosome. If expressed, this gene codes for white, or no color, and is dominant over the alleles that code for a certain color (i.e. orange or black), making the white spots on calico cats. If that is the case, those several genes will be expressed in a blotchy coat of the tortoiseshell or calico kind. But the male, with his single X chromosome, has only one of that particular coat-color gene: he can be not-ginger or he can be ginger (although some modifier genes can add a bit of white here and there), but unless he has a chromosomal abnormality he cannot be a calico cat.”

Though chances of a calico cat being male are extremely low it is not an impossibility. As mentioned above, for a calico cat to be male, the cat typically should have a chromosomal aberration of two X chromosomes and one Y chromosome (XXY) instead of a regular XY pair of chromosomes. However, this chromosomal configuration usually renders a cat sterile with only one out of three thousand male cats not affected by sterility. Considering that calico males are not able to breed, this only further explains how the calico gene is transmitted solely by female calico cats. Aside from being unable to reproduce, male calico cats do not suffer from any other impairment and they are not at any particular health risk due to this mutation in their genes. This genetic characteristic can also be found in humans with a rare genetic condition called Klinefelter’s syndrome or XXY Syndrome. While humans with this syndrome often present more prominent symptoms which may include weaker muscles, greater height, poor coordination, less body hair, smaller genitals, breast growth and less interest in sex, none of these signs are present in calico cats.

The act of reproducing the fur patterns of calico cats by cloning is yet to be realised. Although it has been considered a future possibility, at the moment, it is considered impossible to do so. Penelope Tsernoglou wrote “This is due to an effect called x-linked inactivation which involves the random inactivation of one of the X chromosomes. Since all female mammals have two X chromosomes, one might wonder if this phenomenon could have a more widespread impact on cloning in the future.” Consequently, there is no “breeders’ secret” of interbreeding certain cats in order to obtain this particular coat color mix; in the end, having a calico kitten, relies heavily on chance. Having a calico female cat as the mother is not a one hundred percent guarantee in terms of producing calico kittens.

As a final thought, it’s important for all cat owners to know and fully appreciate the gift of having a calico cat, especially a male one. Most people in general don’t even know that a three colored coated cat is even rare, let alone the specifics of a calico. It is also essential to remember that a “true” calico cat has large blocks of these three colors (orange, black and white) while a “tortoise shell” or “tortie” cat presents a mix of these three colors but they are blended/swirled together more than distinct blocks of color. And, while it is not specific to a certain cat breed, it remains a unique and rare sight to behold.


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