Demystifying the Sex/Color Connection in Cats

Why Does Color Affect the Sex of a Cat? Or Vice-Versa?

You always knew your cat was special, unusual, and certainly unique. But there are even more fascinating facts about the cat that have stumped people for some time. I am referring to what most cat lovers already know: cats of a certain color will be predominantly one sex or another. This has been common knowledge but back in the “dark ages” no one actually knew why. Happily, advances in the field of genetics have uncovered this feline mystery.

It all begins with a very unique genetic twist embedded into the chromosome code of the feline. This is an oversimplification but for the sake of this explanation lets just state that certain chromosomes determine gender (male or female). For example, females have two X chromosomes (XX) and males have only one X chromosome and one Y (XY). Now here comes the twist: a cat’s X chromosome coding is directly linked to the color of its coat! This unique coding is called a sex-linked gene.

Sex-linked gene determines color of cats

Sex-linked gene determines color of cats

Again this is an oversimplification, the coat color in all cats is an X-linked gene for black and orange-brown colors. So the color-coding would be Xb (for black) and/or Xo (for orange-brown). A female cat has two X chromosomes so she is able to “display” two colors at the same time: black AND brown-orange—and all the variations in between (the white color is a separate gene). A female cat with two Xb Xb chromosomes would be black. A female cat with two XoXo chromosomes would be orange-brown.

A male cat on the other hand will only receive his color designation from the one X chromosome and this chromosome would render a monochromatic coat. (The Y chromosome is a “blank.”) For a male to display BOTH red and black he would have to have two of the X chromosomes described above PLUS one Y (for him to be male). This could happen but it would be a mutation (abnormality) that would render him sterile.

The explanation gets a little more complicated when it comes to multi-patterned calicos and tortoiseshell cats (multi-colors of orange, brown, black, gray, cream, or white without patches). These coat colors and patterns are the result of a mutation that occurs during the forming of the embryo. For this to transpire the female will need start off with the Xb Xo combination. During embryonic development some cells randomly—through the process of mitosis (cell division)—will turn off the Xb or Xo gene. This in turn will produce patchy coat pigmentation that results in either a tortoiseshell or patterned calico cat.

As for the orange tabby cat being predominantly male that is true. However female cats can also be orange. It’s mostly a matter of probability. As explained above a male cat has only one color gene and that is located in his X chromosome. So, whatever color that X chromosome has attached to it is what he will be. The X chromosome inherited by the male will either be Xo (brown-orange) or Xb (black)—keep in mind that the white color is an entirely different gene. Therefore the odds are that male cats will be either orange/white; solid orange; brown/dark-brown; brown/dark-brown/white; black/white; solid black; or a dilution of black resulting in gray/white; or solid gray.

The female orange tabby has received two Xo chromosomes. And this does happen, producing females with varying degrees of ginger colors that can be accompanied by white markings. However, she is more likely to receive two different types of X chromosomes such as the XoXb combination. And because of the double X sex-linked color chromosome it is safe to say that female cats will display more color combinations than males.

Simba's unique brown coat is the result of his Xo chromosome that produces the brown-orange color. The white is a separate gene not attached to the X chromosome. Many breed specific cats such as the Siamese and Burmese have specific color-coded genes not related to their gender. Simba's tabby-stripes are visible in his brown coat and reveals the fact that all cats are tabbies, even the "solid" color ones.

Ezra has inherited the sex-linked chromosome Xb resulting in a black coat. A white gene adds a touch of class to this handsome gent.

Ezra has inherited the sex-linked chromosome Xb resulting in a black coat. A white gene adds a touch of class to this handsome gent.

Leon has inherited the sex-linked gene Xo producing a nice red tabby male with alert green eyes.

Leon has inherited the sex-linked gene Xo producing a nice red tabby male with alert green eyes.

Diamond is a lovely blue-cream and apricot medium hair calico. She inherited the sex-linked chromosomes XoXb resulting in the two colors. The pattern she displays is the result of cell mitosis and random shutting off of Xo and Xb resulting in a "pattern." Although she is not a black/red/white she is still considered a calico due to the white markings. She is indeed a wonderful example of genetic color diversification.

Diamond is a lovely blue-cream and apricot medium-hair tortoiseshell. She inherited the sex-linked chromosomes XoXb resulting in the two colors. The pattern she displays is the result of cell mitosis and random shut down of chromosome Xo and Xb resulting in a "pattern." She is indeed a wonderful example of genetic color diversification.

This little calico displays the traditional orange/black/white coloring of a calico cat. She inherited the XoXb sex-linked chromosomes and cell mitosis produced a lovely pattern on her coat. The white is a requirement for the calico color designation. Keep in mind that a calico cat is not breed. It is a distinct color.

This little calico displays the traditional orange/black/white coloring of a calico cat. She inherited the XoXb sex-linked chromosomes and cell mitosis produced the classic calico pattern on her coat. The white is a requirement for the calico color designation. Keep in mind that a calico cat is not breed. It is a distinct color.

Gracie displays the another variation of the chromosome XoXb sex-linked gene. This time the result is a tortoiseshell cat with a tabby stripe pattern, particularly around her head. Her coat coloring is called a dilute tortoisehell because the colors are muted.

Gracie displays another variation of the chromosome XoXb sex-linked gene. The result is a tortoiseshell cat with a tabby stripe pattern, particularly around her head. Her coat coloring is called a dilute tortoiseshell because the colors are muted.

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