Why Are Calico and Tortoiseshell Cats Female?

Cats' coats can come in many colors and combinations; cats can have fur in a solid color, or have markings, spots or patches of different colors. A very common pattern type is that of stripes, lines or dots that create a swirling or marbled effect; these are called "tabby cats", and can be male or female.

Cats can also be bicolor or piebald, that is, have coats with two distinct colors. These cats usually have white fur combined with a different color or pattern. Variations of bicolor coats include tuxedo and van. This type of coat is also common in the two sexes. Tortoiseshell or tortie cats have mottled red, orange or cream and black, brown or blue coats. The proportions of each color are variable.

However, cats can have more than two colors. Calico cats have tortoiseshell coats with white patches, which is why they are also called "tortoiseshell-and-white" or "tricolor". As you will see, tortoiseshell and calico coats are almost exclusive to female cats.

The color and pattern of a cat's coat depends on the animal's genes; more specifically, the information for hair color is coded into the two chromosomes that determine the animal's sex. Therefor, the color and pattern of the cat's coat is a feature that is linked to its sex.

Chromosomes are structures found in the nucleus of cells that contain all of a living organism's genetic information, that is, its DNA. Cats have 38 chromosomes: 19 are provided by the mother and 19 from the father.

Sex chromosomes are the ones that determine the sex of the cat. Cats, like all mammals, have two sex chromosomes: X and Y. The mother always gives an X chromosome, and the father can give X or Y. Depending on the combination, the cat can be male or female.

• XX: Female
• XY: Male

The information for black and orange colors are in the X chromosome. In other words, for these colors to show, the cat must have the X chromosome. Males only have one X, so a male cat will only be either black or orange. Females have two X chromosomes, so they can have genes for both black and orange and thus create tortoiseshell patterns.

The white color, however, is not linked to sex chromosomes. This is why a female cat can have three colors and therefore a tricolor or calico coat: they have an X chromosome for black, an X chromosome for orange, and white is expressed independently.

Depending on the chromosomes it has, a cat will express one color or another. Black and orange colors are encoded in the same chromosome, X. If the X chromosome is present, it will have one allele or another. X0 will be orange and Xo will be black. If the two alleles happen at once, which can only happen in a female cat, a tortoiseshell coat appears.

Female cats can inherit three chromosome combinations:

• X0X0: orange cat
• X0Xo: tortoiseshell cat
• XoXo: black cat

Male cats can only inherit two chromosome combinations:

• X0Y: orange cat
• XoY: black cat

As we said, white color is determined by the W gene (white) and it is expressed independently. This is why cats of all sexes can show white and other combinations, such as black and white, orange and white, and solid white, but female cats have the possibility of showing all three colors at once.

There are several types of tricolor coats in cats. They only differ in the proportion of white or type of pattern of their coat:

• Calico or tricolor cats: These cats show wide and noticeable white patches, and they can be mostly white, especially on the abdomen, legs, chest and chin. They show black and orange spots on their coat, which can appear diluted (blue or gray, cream) on the skin. In the picture you can see a calico cat.
  
  
• Tortoiseshell or tortie cats: These cats have coats with asymmetrically mixed black and orange, often diluted into lighter shades. There can be white mottling. Tortoiseshell cats are usually predominantly black.
  
  
• Tortie-tabby or torbie cats: These cats's coats have tortoiseshell combinations, but instead of solid colors, the black or orange parts - or both - are striped or brindled, as in a tabby cat.

Yes. Male tortoiseshell and calico cats do exist, but it is very rare to see them. The coat pattern is caused by a chromosomal abnormality: instead of having two sex chromosomes (XY), which would prevent them from showing orange and black at once, these cats have three (XXY). Because they have two X chromosomes, tortoiseshell and therefore calico patterns can be expressed just like in females.

This is known as Klinefelter syndrome and usually causes sterility. This is a rare condition, but it banishes the myth that all tortoiseshell and tricolor cats are females. However, it is so rare - it only happens in 1 out of 3,000 male cats - that if you come across a tortoiseshell or calico cat you can assume that it is probably a female.

Do you want to learn more about cats? Keep browsing AnimalWised and discover:

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• How to clean a cat without bathing

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