Calico Girls and Orange Boys: Cat Color Genetics

What does a cat’s sex and coat color have to do with genetics? Everything! A quick overview of cat colors is an easy way to understand how genetic traits are passed along.


Any cat person can tell you that orange cats are usually male and tortoiseshell/calico cats are usually female. The reason why is simple. All variations of cat colors are either red-based or black-based. The red color is sex-linked because it is carried on the X chromosome. A male (XY) has one X chromosome, so if he carries a red gene, he will be red. Females (XX) would need two red genes to be red, and this rarely happens. If a female has one red and one black, the tortoiseshell (black and orange) coloring will result. Calico is black and orange mixed with white.


On the flip side, all-black coloring is more common in males than females because a male only needs one gene to be black, while a female needs two. Females that are either all red or all black are uncommon, but they do exist. Even rarer is a tortoiseshell male (usually sterile) because he will have an extra X chromosome.


Hair length is also controlled by genetics. The gene for short hair is dominant and the gene for long hair is recessive. Short hair is more common in cats because it will be dominant even when carried by just one member of a chromosome pair. Long hair only occurs when both members of a chromosome pair have the gene.


What about the supposed connection between white fur, blue eyes, and deafness in cats? This is true in some cases. There are 3 genetic causes of white coloring in cats: albino white, dominant white, and white spotting.


White spotting produces those familiar “tuxedo” white socks and bib markings. White spotting can also occur on all-white cats. It is this white spotting that causes blue eyes (or one blue eye) and deafness. If the white spotting spreads to the eyes, they will be blue. If it spreads to the ears (or one ear), it will cause degeneration of the inner ear (cochlea) shortly after birth and result in deafness.


Congratulations, you just passed Cat Genetics 101…good job!


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  • Aaron Seminoff
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