Calico is a mix of orange, black, and white fur found on certain cats. Not all
calico cats are female, but the vast majority are. Why? Like a lot of life's mysteries, it has to do with genetics.
PetPlace.com gives a surprisingly detailed explanation. Half a cat's chromosomes come from the mother, and half come from the father. The gene that determines a cat's coloring is found on the X chromosome.
Female cats have two X chromosomes, and each one can carry a different color. "In calicos...one X has the black gene; the other X has the orange gene." At some point in the female cat's development, one X chromosome becomes inactive. The timing of this determines the amount of calico patches.
So calico coloring isn't that uncommon among female cats. It's just a matter of the right chromosomal combination. In males, things are more complicated because they only have one X chromosome and "it's never inactivated."
A male cat can be calico if it's created with "two X chromosomes and a Y, allowing one X to be inactivated." This is a genetic defect known as XXY, and it's very rare. In fact, only
one out of every 3,000 calicos is male.
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