If the orange color is sex regulated, how does it also appear on the females?
In: Biology
Orangeness is determined by the O allele, which is on the X chromosome. O, for orange, is relatively uncommon and o, non-orange, is the majority of the cat population. For quick terminology review, a gene is the area of DNA that produces some protein, and alleles are the different types. O produces the protein that makes orange hair, and o doesn’t. Because we have two of most chromosomes, most of them (autosomes) we have in pairs, so the genes on those chromosomes also have two alleles in each of us, which can be the same or different. X and Y chromosomes are a pair too, but Y is tiny and doesn’t have much on it, so most of the chromosomes are only on X, and males only have one while females also have a pair of alleles.
Most cats aren’t orange or calico and have only one (male) or two (female) o alleles. If they inherit one O, males are orange but female most likely have O and o, so they are calico. A female with an orange father (O) and calico mother (Oo) can inherit two O’s and be orange. A cat with two orange parents (O and OO) will always be orange.
Calico happens because each cell in cats or humans has only one active X chromosome, and which one is active is random early in development but not at the beginning. So one chunk has O and a orangish, and another chunk is o and looks brown/black, and the mix produces calico.
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