How does the Y chromosome influence sex determination in humans?

In humans, the Y chromosome is the primary genetic determinant of male sex. While all human embryos possess the potential to develop into either sex, they follow a default path toward female development unless specific masculinizing influences occur during gestation.12

The Y chromosome influences this process through the following mechanisms:

• Testis Determination: The Y chromosome carries specific genes—often referred to as maleness determiners—that direct the undifferentiated embryonic gonads to develop into testes.12
• Hormonal Signaling: Once formed, the testes in XY fetuses secrete Müllerian inhibiting hormone, which causes the female-precursor ducts to atrophy. Simultaneously, the testes produce testosterone, which stimulates the Wolffian ducts to develop into the male reproductive tract.1

If these Y-linked signals are absent or if the body fails to respond to them, the genitalia will develop in the female direction, regardless of the presence of testes. Conversely, normal female development requires two X chromosomes, as the X chromosome also plays an active role in the development of functional ovaries.1