Why are calico cat predominantly female?

It is a well known fact that calico cats are mostly female; male calico cats do exist, but this can only happen if the cat has Klinefelter Syndrome, which will be explained later. The reason why only female calico cats is because of a concept called Sex-Linked Genes, a concept that certain traits are determined by the sex chromosomes of an organism.

This diagram shows the X and Y
chromosome relationship with fur
color. 

Fur color in cats is determined by the X chromosome, so in most cases, the genotype of the mother cat will determine what kind of fur color the offspring will have. Since male cats have one X chromosome and one Y chromosome, the male cat's color will be determined by the one X chromosome. For example, if the mother has a X chromosome that expresses orange fur, the son will have orange fur. If the mother has black fur, the son will have black fur.

This idea is more complex in daughter cats. If a daughter has two X chromosomes that express the same fur color, a process called Lyonization will occur. Lyonization is a process that occurs during the blastula stage of embryonic development, and arises randomly in each cell. In each cell, one of the X chromosomes is coiled into a Barr Body, leaving the remaining X chromosome of express the trait. For example, if a daughter has two X chromosomes that express black fur, then one of those chromosomes will become a Barr Body, and the other chromosome will express the black fur in the phenotype. Once again, this is only at the cellular level

Calico cats have two different kinds of X chromosomes- one that expresses black fur and one for orange fur. The cats will not express both of these traits in the same cell; instead, each cell will express only black fur or only orange fur. In Lyonization, both X chromosomes will be separated, and be accompanied by their own Barr Body. Afterwards, each cell will arise from either the X chromosome that expresses from orange fur, or from the X chromosome that expresses black fur. This results in various patches that occur throughout the body called a tortoiseshell coloration.

Male calico cats are the result of Kilnefelter Syndrome, which is when a cat has two X chromosomes and one Y chromosome. The two X chromosomes will be one that expresses orange fur and one that expresses black fur. The only problem with this process is that the male calico cats become unfertile.

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