Question

Calico cats have a randomly patterned coat. Which of the following correctly describes why this occurs?

A		Two copies of the X chromosome are expressed in some portions of the cat’s fur, but in others, one of the copies of the X chromosome has been randomly silenced.
B		The gene for coat color is located on the Y chromosome, which is only expressed in regions of the body not important in sexual characteristics, including the fur.
C		The gene encoding coat color is located on the X chromosome. In different parts of the body, one or the other X chromosome is randomly shut off.
D		As cells divide, the X chromosome previously sequestered to the Barr body is reactivated causing an alternation in coat pattern.

Answer 1

a. Two copies of the X chromosome are expressed in some portions of the cat’s fur, but in others, one of the copies of the X chromosome has been randomly silenced.

In calico cats, random silencing of one of the X's in each cell creates the distinctive pathcwork of coats in them.