Why is female orange cats are very rare?
It’s not that orange female cats are rare, it is simply that an orange cat is more likely to be a male. For a female cat to be orange, she must inherit two orange genes — one from her mother (orange, calico, or tortoiseshell) and one from her father (who must be orange). A male cat needs only one orange gene, which he gets from his mother (orange, calico, or tortoiseshell). This is because the gene that codes for orange fur is on the X chromosome, and like humans, females have two Xs and males are XY. Genes on the X chromosome are said to be sex-linked.
Why is it super-rare to see a male calico cat?
Because in order for a male to be a calico, he must have the feline equivalent of Kleinfelter Syndrome and he is an XXY male. Because a calico male has an extra X chromosome, he is most likely sterile (cannot father kittens).
How fur color inheritance works in calico/tortoiseshell and orange cats?
Orange fur is due to what is known as dominant epistasis. It actually changes black pigment into orange! This is an example of gene interaction — where one gene changes the expression of another.
Calico or tortoiseshell coloration is the result of something called X-inactivation (also known as dosage compensation). Female mammals (including humans) have one X in every cell inactivated (shut down) as an embryo. In approximately half the cells, the paternal X (one from the father) is expressed, and the other half of the cells the maternal X is expressed. So when you look at a calico cat, where you see black fur –that came from one parent and where you see orange fur, that came from the other parent. Thus all female mammals are genetic mosaics!
How many genes are involved in determining a cat’s fur color?
Many. Here are a few of them:
Agouti vs. non-agouti: Provides the lighter fur background with striped cats.
Black vs. non-black
Color deposition: Determines how pigment is deposited, and also affects eye color.
Dilute vs. non-dilute: Gray is a diluted form of black and tan/beige is a diluted form of orange.
Spotting: If two dominant genes are inherited, a cat will have white on more than 50% of their body. If a cat has one dominant and one recessive gene, then the cat will have white fur on less than 50% of their body. If she gets two recessive genes, there will be no white on the body!
White vs. non-white: Just one white gene and the whole cat will be white! It is called a masking gene. A white cat could have the genetics to be a calico, black or any color cat but the white gene hides the other genes’ expression and the cat appears all white. White cats are not albinos unless they have red eyes. Albino cats are extremely rare and albinism is the result of color deposition and not the white gene.
There are also genes for tabby stripping, silver tipping and seal-pointing.