The 23rd pair of chromosomes are the sex chromosomes. There are two types of sex chromosomes, an X and a Y. The X chromosome is a sex chromosome that both males and females have (females have two X chromosomes). The Y chromosome is the sex chromosome that contains one gene that signals a series of chemical events to occur during prenatal development, which together, result in the development of a male child. This Y chromosome comes only from the father, so if chromosomes from two women were combined to produce a child, they would be unable to produce a male.