clipped from www.nytimes.com

To be fair, the biology of sex is a lot more complicated than the average fan believes

If the person has XY chromosomes, you declare him a man. If XX, she’s a woman. Right?

Wrong. A little biology: On the Y chromosome, a gene called SRY usually makes a fetus grow as a male. It turns out, though, that SRY can show up on an X, turning an XX fetus essentially male. And if the SRY gene does not work on the Y, the fetus develops essentially female.

Even an XY fetus with a functioning SRY can essentially develop female

In the case of Androgen Insensitivity Syndrome

the genitals and the rest of the external body look female-typical, except that these women lack body hair

Moreover, a person can look male-typical on the outside but be female-typical on the inside, or vice versa

Matthew, a 19-year-old who was born looking obviously male, was raised a boy, and had a girlfriend and a male-typical life. Then he found out

that he had ovaries and a uterus

he had XX chromosomes

his body developed

male-typical