Answer: In cats, one of several genes controlling fur color is located on the X chromosome. The gene has two versions, or alleles. One form of the gene codes for orange fur (XB), and the other form codes for black fur (Xb). While it's difficult to say which allele is dominant and which is recessive, since only one is ever expressed (see below), let's say, for the sake of argument, that orange is dominant to black. Ordinarily, this would mean that an animal inheriting one copy of each gene (genotype XBXb) should have orange fur. Surprisingly, a female cat heterozygous at that locus (XBXb) will not be orange. Instead, her coat will be a patchwork of orange and black, a condition known as tortoiseshell. Male color expression is straightforward. Because only one allele exists for the gene in each cell, it will be expressed. And all males have only B or only b. There are no heterozygotes, because the Y does not carry the allele.
Step-by-step explanation:
I got this from an article! I hope this helps.