and all of the somatic cells in human males contain one X and one Y chromosome (Figure 3). The same is true of all other placental mammals — males produce X and Y gametes, and females produce ...

The X and Y chromosomes, commonly referred to as the sex chromosomes, are one such pair. They determine the biological sex, reproductive organs, and sexual characteristics that develop in a person.

"You either have XX or XY chromosomes," Rep. Nancy Mace, R-S.C., wrote Feb. 20 on X. "Those are the options." Most commonly, a person is born with two X chromosomes (female) or an X and a Y (male).

Why are the human sex chromosomes called “X” and “Y,” while the other 22 chromosomes are identified only by numbers? The answer begins in the late 1800s, when insect gonad cells, whose large ...