Long-haired orange female cats hard to find, genetically speaking

Posted: Wednesday, May 17, 2006

Linda Daniel


The woman was buying greeting cards, all featuring orange cats. "I have two of them," she explained. They're brother and sister."

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"You have an orange female? That's unusual, you know," the clerk replied. "I read somewhere that only one out of three orange cats is a girl."

"One out of four," the customer replied.

"One out of a hundred," piped up a voice from within the shelves.

Then they burst out laughing because cat genetics was such an unlikely topic for a spontaneous conversation - even considering the impact on the brain of thirty-something straight days of rain. And I went home to check the Internet to see which of them was right. Turns out, they all had a piece of the truth.

To be born wearing an orange coat, a female kitten needs to inherit the orange gene from both parents. There are three variations on the orange theme. A female kitten has a equal chance of being born orange, tortoiseshell or calico. Tortoiseshell coats are orange and black with the two colors swirled together. Calico coats are tri-colored, with distinct patches of orange, black and white.

All of the orange males in the litter will be simply orange. (Orange cats with white patches are included in the "orange" category.) But having both orange and black in the coat is strictly a female trait.

Since half of all kittens are males and half are females, we get three orange males for each trio of females - one orange, one tortoiseshell and one calico.

Genetically speaking, there is no such thing as a male tortoiseshell or calico. Once in a very great while, such a kitten is born as a consequence of nature fumbling when cells are combining. It's a birth defect that affects 1 out of every 3,000 tortoiseshells and calicos. Most of these males are sterile. Only one in 10,000 of them is able to reproduce.

So all of this adds up to the 3-1 ratio cited by the clerk. That's when you're looking only at those litters produced by two cats with orange genes - the only pairing that can produce an orange female.

There are many other pairings in which only one of the parents carries the orange gene. These parents, too, can have orange kittens. However, all of those redheads will be males.

Figure that into the equation, and you get into the ballpark of the ratio cited by the customer: one orange female for every four orange males.

Rarest of all the orange females is the one with long hair. Short hair is a dominant trait; long hair is recessive. Breed a long-haired cat with a short-haired one, and the majority of the offspring will have short hair. Put that together with the small number of orange females, and getting a long-haired female is a real long shot - one out of 100 orange cats.

There is an ancient Egyptian myth that is relevant. It goes like this:

Heroic humans set out to slay a dragon that was the source of all chaos in the world. The dragon was known as A-Pop. When the humans cornered him and struck a killing blow. A-Pop did not die, but flew into a million fragments. The pieces of A-Pop remain suspended, one fragment reappearing in each long-haired, orange female cat.

For those of you who have long-haired orange females, this explains a lot.

• Linda Daniel has spent her life in the company of cats, most of whom simply showed up at her door. She's a believer in spaying and neutering to reduce the number of homeless cats.

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