Did you ever wonder why most orange, or ginger, cats are male? Well, the mutation that causes a cat’s coat to be ginger rather than the usual shades of brown and black is inherited differently from other coat colors. It relates to the “dominance” rule in genetics. When a gene trait is “recessive”, it has to be present on both chromosomes that the animal inherited each from his or her mother and father. Otherwise, the other “dominates”. Usually, animals with one dominant and one recessive gene are indistinguishable on the outside from animals with two dominant versions of a gene. The dominant gene, or genes, take over the trait characteristics.
However, there is one major exception to this rule. If a cat carries one orange and one brown version of the gene for coat color, then both appear in the coat, in random patches. That would be the explanation for a tortoiseshell-tabby or “tortie” cat, where we see the result of the chromosome with the orange version switched on, and in another part of the skin it is the brown-black pattern that “wins”. The precise color of the patches depends on other coat-color genes. So, if the cat also caries (two copies of ) the black mutation, then the brown patches are black, so their tabby pattern is obscured (producing a regular black cat). While within the orange patches, upon which the black mutation has no effect, you see orange and yellow with the tabby pattern still visible, producing a tortoiseshell or calico.
Second, the gene itself is carried on the X chromosome. Female cats have two X chromosomes. Males have only one, in addition to only one copy of the much smaller Y chromosome that makes them male, but which carries no information about coat color. Thus, for a female cat to be orange, it must carry the orange mutation on both chromosomes. That is statistically much harder to do, and thus, approximately 95% of orange cats are therefore, male. If a female cat has only one orange coat color gene, it will outwardly have a tortoiseshell coat. For this reason, tortoiseshell cats are almost always female. AND, the only way for a male to be tortoiseshell, he has to have two X chromosomes and a Y chromosome, the result of an abnormal cell division. So that is an even rarer situation. A common misperception holds that ginger, or “marmalade”, cats are always male, hence the phrase “ginger tom”. Still, if you are going with the odds, orange cats are more likely to be male. But go ahead and make sure your vet checks just in case, and BEFORE he is scheduled to be neutered, and turns out to be a rare female!
Hope you found this brief genetics lesson interesting, cat lovers!
Dr. Dawn
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