what determines whether a person is male or female
Sexual differentiation in humans The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote.[3] Females have two X chromosomes, and males have a Y chromosome and an X chromosome. At an early stage in embryonic development, both sexes possess equivalent internal structures. These are the mesonephric ducts and paramesonephric ducts. The presence of the SRY gene on the Y chromosome causes the development of the testes in males, and the subsequent release of hormones which cause the paramesonephric ducts to regress. In females, the mesonephric ducts regress.