If the cat only has these two colors, it is known as a tortoiseshell cat. Those two colors then combine on the cat’s fur to create the orange and black patches of fur. In both cases, these cells are replicated and the inactivated chromosome will always stay inactive. Other cells use the chromosome for black fur instead. One cell inactivates the chromosome for black fur resulting in orange fur. However, the offspring receives the chromosome for, for instance, black fur from one parent and orange fur from the other. In the case of calico cats, the same process occurs. So, for instance, if the female offspring receives the chromosome for black fur from both of its parents, she will have black fur. Likewise, another cell may silence the X-chromosome from the father and instead use the chromosome from the mother. That cell then creates more cells, each of which will use the father’s X-chromosome to determine the fur color. One cell may shut off the X-chromosome from the mother while leaving the chromosome from the father. The important thing here is that the same X-chromosome does not inactivate for each cell. Each cell only needs one X-chromosome, so early on when the feline embryo is developing, one of the two gets shut off, with the inactivated one supercoiling into something called a “Barr Body.” But females receive an X-chromosome from both the mother and father. A male offspring only receives an X-chromosome from his mother, so that alone determines his fur color. Why is this so important to the topic at hand? Because in cats the X-chromosome determines most of the fur color (with the potential exception of white). This is true for both humans and cats, along with many other animals. Thus, a female receives an X-chromosome from both of her parents while a male receives an X-chromosome from his mother and a Y-chromosome from his father. This allows them to pass down either an X-chromosome or a Y-chromosome to their offspring, determining the genetic gender.
Males, on the other hand, have an X-chromosome and a Y-chromosome. As you may or may not be aware, females have two X-chromosomes, meaning that they can only pass down an X-chromosome to their offspring.
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