The inactivation of one X chromosome is also done in humans. The reason it occurs in patches is that it happens randomly in each cell early in development. Progeny cells keep the same pattern of inactivation. So there will be patches of cells all with the same X chromosome inactivated. Patterns like this are called mosaics, and calico cats are the classical example used in all the textbooks. BTW, the white color underneath is due to another gene entirely.
I have a sixteen year old Tortie. She is definitely the queen of the house. She is also very much a bitch. She will not tolerate another cat in the house at all! Our daughter brought a kitten home for Christmas break last year. She tried to sneak the little thing up to her bedroom but our cat saw it. She not only was out to get the poor little kitty, she was outwardly hostile towards our daughter- her owner from birth! She can be a sweet cat, as long as everything goes her way. I had no idea a cat would hold a grudge.
tomas, my best friend’s calico is just like your cat! Same age, same attitude toward other cats… come to think of it, she’s only marginally more accepting of strange humans. 
Yet when my friend goes away for a few days and comes home, she is so happy to see him that you can hear her purring in the next room, and she drools like crazy. Go figure!
I have a white cat with one blue eye and one brown eye. Did you know that white cats with blue eyes are always deaf? (My cat isn’t, since her eyes are different colors)…she’s sooo cute, but VERY high strung and shy.
Both of my torties are sweethearts. One is so adorable that everyone falls in love with her. She’s even-tempered, friendly, loves to have her belly rubbed, always wants to sleep beside us, and cries if no one’s around. The other isn’t quite so open and gets irritated easier, but she loves to be petted and also calls for attention. Neither cat has ever scratched or bitten anyone (unless you deliberately annoy them so much that they don’t have a choice). My vet also said that a male tortie is extremely rare. Neither cat has any white on them, and one is more orange than black (extraordinarily beautiful cat, btw).
My calico is certainly temperamental and unpredictable. One moment she is rolling on her back purring and begging for a belly rub, then next moment she is slashing and hissing, but that is only with other people usually. My wife says the cat is slavishly devoted to me, which is kind of true, but not wholly true. Every now and then she’ll get into a snit and slash at me too, but most of the time she curls up on my chest, puts her nose up to mine and goes to sleep. The cat also has an uncanny antipathy towards my mother-in-law: she really hates my mother-in-law; she’ll slash and pounce without any provocation, helping to keep the mother-in-law away from my home. * ** Good cat! Good Cat!* **
I’ve known about half a dozen calicoes in my lifetime, and one was an absolute sweetheart, but then again, another one decided one day that my sister’s face ought not to be attached to her head.
Does anyone have any idea why calicos might have a predisposition to ill tempers?
Is no one going to say how pretty my calico Piper is?
White cats with blue eyes have a higher incidence of being deaf but this is not always true. I have a white cat with blue eyes and he hears just fine!
As for the calico/tortie attitude, ask your vet next time about this. As I said earlier, it is just anecdotal evidence, but at every clinic I have ever worked at, when we have a calico or tortie and it misbehaves, we shrug and say, “Typical.”
And yes, Piper is very pretty! Are those tabby patches on her though? Wouldn’t that make her a “torbie” or something? Ah, who cares, she’s cute.
Thank you, Cyndar, for that spontaneous and unsolicited endorsement!
I don’t know what you mean about “tabby patches”…Piper has some tabby-ish striping, but the colors are strictly orange, black and white, like any calico. I sometimes call her “Mars kitty” because her colors resemble that planet.
Her brothers are tabbies, though. Jack (who I don’t have a digitized photo of) is all tabby except for a white ascot, while Buster is tabby and white in patches.
“BTW, the white color underneath is due to another gene entirely.”
Actually the white in calicos is the result of a lack of pigmentation in those regions of skin as opposed to a specific gene. During embryonic development some cells are established early on as being melanocytes which are the cells responsible for producing pigment and thus hair or skin color. Normally during development these cells migrate out from the neural tube (which becomes the spinal cord) and end up evenly distributed throughout the skin. Sometimes the migration is not as complete which leaves areas of unpigmented skin which is seen as white fur. This is why the white patches usually show up on the belly and extremities, but rarely the back of the animal.
Interestingly this also accounts for the high incidence of deafness in white cats. If a cat is totally white due to lack of melanocytes it means that these cells were never established. Melanocytes are also normally present in the cochlea and are required for normal hearing. If the cat has no melanocytes it cannot hear. Some white cats can hear, but their color is not due to lack of melanocytes, but rather a lack of pigmentation in the melanocytes.
John
My aunt’s all white cat with blue eyes is deaf.
We have another all white cat with greenish brownish eyes. She’s a Turkish Angora, though…
Just want to weigh in against the evil-tempered calico generalization. We have Emma, a calico who is about nine months old. She gets along with everyone, including our other five cats. Purrs like a little motorboat she does and loves tummy rubs.