A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by __________.1. X chromosome inactivation
2. An operon
3. RNA splicing
4. A homeobox
5. A mutation

X chromosome inactivation is a process that shuts down one X chromosome in all the cells of a female during early embryonic stages. It is done to balance the dosage of X-linked genes in males and females. The process of X chromosome inactivation is random which means that either paternal or maternal X chromosome may be inactivated in the cells. The inactivated X chromosome in a cell is transmitted to all of its daughter cells.

Therefore, some cells of a female express the paternal X chromosome while others express the maternal X chromosome. The random expression of the paternal or maternal X chromosome in females results in patches of cells with or without sweat glands.