* Females have two X chromosomes (XX).
* Males have one X and one Y chromosome (XY).
The Y chromosome contains the SRY gene, which is the key factor in male development. When the SRY gene is present, it triggers a cascade of events that leads to the formation of testes.
Here's a simplified breakdown:
1. Fertilization: An egg (X chromosome) is fertilized by either a sperm carrying an X chromosome or a sperm carrying a Y chromosome.
2. XY Embryo: If the sperm carries a Y chromosome, the embryo will be XY and develop as male.
3. SRY Gene Activation: The SRY gene on the Y chromosome becomes active, causing the gonads (which are initially undifferentiated) to develop into testes.
4. Testosterone Production: The testes begin producing testosterone, a hormone that triggers further male development, such as the growth of male genitalia and the development of secondary sexual characteristics.
It's important to note that:
* Other genes play a role in sexual development beyond just the SRY gene.
* Environmental factors can also influence sexual development, although these are generally less significant than genetic factors in mammals.
* Rare genetic conditions can result in individuals with unusual chromosome combinations or mutations in genes related to sex determination, leading to variations in sex development.
Let me know if you have any more questions!