She’s just a girl
I’m sure you’ve seen this kind of cat before. But have you ever thought about its unique color and why it is the way it is? Let’s find out!
Calico
This is a calico cat, a cat with three different coat colors (white, black, and orange). This domesticated cat is expected to be female most of the time, while the male calico cat is extremely rare. Why? because the black and orange colors are linked to the X chromosome, while the white color is determined by autosomal chromosomes.
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Quick refresher: organisms have two types of chromosomes: autosomes and sex chromosomes. Autosomes determine the traits (for example, hair color, eye color, hair texture), while sex chromosomes determine sex (XX for female and XY for male).
Random X-inactivation
A calico’s tricolor comes from something called random X-inactivation. Since the genes for black and orange fur sit on the X chromosome, a female can carry one X with the ‘black’ version of the gene and one X with the ‘orange’ version. But here’s the twist: a female with two different-color X chromosomes (‘black’ X and ‘orange’ X) will randomly shut off one X completely in each cell as she develops. So, some patches of her skin end up using the ‘black’ X and other patches end up using the ‘orange’ X, plus the white patches come from that separate autosomal gene. Thus, you get the classic calico look. Males, on the other hand, only have one X chromosome (they’re XY, remember?), so there’s no second X to create the patchwork. That’s why male calicos are very rare.
Male, rare, sterile
However, these rare exceptions can occur when there’s an error in cell division during gametogenesis (the process of forming sex cells: sperm in males and eggs in females). This error gives an extra X chromosome, making him XXY instead of the normal XY. As a result, he carries two different-color X chromosomes (‘black’ X and ‘orange’ X), allowing the calico pattern to appear despite being male. This is analogous to Klinefelter’s syndrome in humans, and it’s the reason male calico cats are almost always infertile.
Has personality
Another interesting bit: calico cats were reported as somewhat frequently more aggressive to humans in certain contexts (during veterinary visits, during handling, and during everyday interactions). Though this finding still needs more replication before being a solid scientific fact, consider yourself warned and don’t be too surprised if your calico gives you a little attitude every now and then hehehe.
Anyways, whatever their color, we love them all! They’re just as sweet as cats of any other color. And from now on, if you see a calico cat on the street, you’ll know it’s most likely a girlypop👑.
