A recent Trump executive order defines sex based on gamete size. But the order oversimplifies genetics, hormones and reproductive biology.

Female (XX) mammals inherit one X chromosome from each parent, but males (XY) receive an X from their mother and a Y sex chromosome from their father. X and Y chromosomes determine not only the ...

"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).