Here's how it works:

* Females typically have two X chromosomes (XX).

* Males typically have one X and one Y chromosome (XY).

The Y chromosome contains the SRY gene, which triggers the development of male characteristics. Without the Y chromosome and its SRY gene, a person will develop female characteristics.

It's important to note:

* Biological sex is complex and not solely determined by chromosomes. There are many factors that influence how a person develops, and there is a spectrum of biological variation.

* Gender identity is separate from biological sex. It's how a person feels about their own gender, and can be different from their assigned sex at birth.