Why orange cats are usually male

Have you ever wondered why orange cats are usually male? And why calicos and tortoiseshells are female? For decades, scientists at leading universities have explored why cat fur color is linked to sex. 

Now, building on past work, researchers at Stanford University and Kyushu University have each conducted independent studies and found a definitive answer. 

It all has to do with a long-posited but elusive genetic mutation – a DNA deletion near a gene called ARHGAP36. This mutation causes pigment cells to produce a ginger hue. At the same time, it suppresses the cells that create brown or black coloring. 

The X sex chromosome contains the genetic instructions for orange fur. Most fully ginger cats are male because they typically have only one of these chromosomes.

Female cats, on the other hand, normally have two X chromosomes. For a female kitty to have a fully orange coat, both X chromosomes must activate the genetic instructions for that color. More usually, only one of her X chromosomes carries the ginger trait. The result is a calico or tortoiseshell cat, with a mottled or patchy coat of orange, black and gray. 

Other mammals – such as tigers, golden retrievers, or red-haired people — often have ginger coloring. But in their case, pigmentation isn’t linked to sex chromosomes. This means individuals of both sexes will display this coloration. Domestic cats appear to be the only species where orange coloration is linked to sex.

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