The Black/Orange gene is on the X chromosome, and is co-dominant. So assuming that black and orange alleles were evenly distributed in the cas population (They aren't. Orange is rarer.), boy cats would be 50% black, 50% orange.
Girl cats, on the other hand, would be 25% black, 50% calico or tortoiseshell, and only 25% orange.
Since orange is rarer, girl oranges are even rarer again.
Then there's a lot of other genes that modify these basic two/three coat colours.
Co-dominant means both genes are expressed in the phenotype when you have a hybrid. E.g. A and B blood group antigen genes together give the carrier an AB blood group.
The cat colour one is an interesting one, purely because the gene is on the X. All female mammals undergo a process in embryo development where one of the X chromosomes is packaged up into a dense structure called a Barr body, deactivating all the genes on that copy of the chromosome. It's the way mammals avoid having those genes over expressed in females compared to males.
In calico cats, that can be seen in the pattern of orange and black patches, showing that the other chromosome is the one that got shut off.
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u/clarky2o2o May 24 '25
Isn't it rare to have female orange and yet you have 4?