Did you know that calico cats are almost always female?

Cats present coats of an infinite variety of shades: from Pearl gray of a Persian cat to the cream color of a Siamese going through the orange, black, or multicolored furs. Now, when we see a cat with 3 colors: orange, black, and white we can almost certainly know that it is a female

Fig 1: Calico cat: orange, black and white spots. With 99.97% certainty, it will be a female.

Let´s start from the beginning; we can assure that a cat with a two color coat, specifically orange and black, practically with total certainty will be a female.

The reason lies in genetics, in order for a cat to be a male, he has to have a chromosome X and another chromosome Y (XY) while a female has to have a couple of X chromosomes, therefore XX. The orange color in cats is found in the X chromosome, the fact that a cat is orange or not is related with its gender; since for a cat to be able to express the orange color in its coat, one of these circumstances must happen:

  1. The cat is XY (male) and in his chromosome X carries the dominant gene “O” (Orange) which will make the cat orange. If the gene isn’t dominant, we will name it “o” and it will not express the color orange, so the cat will be of a different color that will come from other genes not connected with the X chromosome. Y chromosome is irrelevant for the cat color.
  2. If the cat is a female (XX): in this case it is possible that both chromosomes carry the dominant gene “O”, if this happens the cat will be orange. If the gene in both chromosomes is recessive “o” the cat won’t be orange, it will be black since it´s the color that will manifest in this case.

If the cat has the gene “O” in an X chromosome and in the other X chromosome the “o”, orange won´t be totally dominant and the color black which accompanies the gene “o” will also appear so the cat will be bicolor: orange and black. Some call these cats tortoiseshell.

Since males can´t have two X chromosomes (except genetic anomaly as we will see later) they can’t have a gene “O” and another “o” therefore they can´t be bicolor orange and black.

Fig 2: Tortoiseshell cat: Black and orange coat

Then, why if I see a cat that is 3 colors: orange, black, and white is it a female? The fact that white spots show up in an orange and black cat depends on a different gene (in this case not located in the X chromosome) which will determine if the animal’s hairs will have that pigment or not. For this reason if a female cat has this dominant gene, it will have white spots together with the orange and black tonalities, creating a tricolor animal. As we already know that black and orange cats can only be female, also tri-colored cats can only be female.

Like every rule, this one also has its exception: it is possible that a male cat isn´t XY but XXY. It is a chromosomic alteration very infrequent but it can happen and does occur, although it is extremely rare. Studies show that the probability is 0.03%. In this case, the cat (male) could be orange and black since it can gave two genes “O” and “o”, which a normal cat can´t have like we have seen previously.

In any case, if you see a calico cat, odds are that 99.97% of the times it is a female. It is a pretty safe bet.

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2 thoughts on “Did you know that calico cats are almost always female?

  1. In its final sentence, the eighth paragraph contains two errors, which contradict points made throughout the rest of the article:
    “As we already know that black and orange cats can only be male, also tri-colored cats can only be male.” (‘male’ should read ‘female’ in both cases).

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