* Sex chromosomes: Humans typically have two sex chromosomes: X and Y.

* Females have two X chromosomes (XX).

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

* The SRY gene: This gene is located on the Y chromosome and is considered the primary determinant of maleness. It codes for a protein that triggers the development of testes in the embryo.

Here's a simplified breakdown:

1. Presence of Y chromosome: If an embryo has a Y chromosome, the SRY gene is activated.

2. SRY gene activation: This leads to the development of testes, which produce testosterone.

3. Testosterone production: Testosterone drives the development of male characteristics like internal and external genitalia.

Absence of Y chromosome: If an embryo does not have a Y chromosome, the SRY gene is not activated. This leads to the development of ovaries, and the absence of testosterone allows for the development of female characteristics.

Important Note: This is a simplified explanation. Sex development is a complex process, and there are many other genes and environmental factors that can influence it. Variations in these factors can lead to intersex conditions, where individuals may have a mix of male and female characteristics.