Sex determination and differentiation (human)

Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination.Sexual differentiation includes development of different genitalia and the internal genital tracts, breasts, body hair, and plays a role in gender identification.

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. 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.

Divergent sexual development, also known as intersexuality, can be a result of genetic and hormonal factors.

A baby’s genetic sex is determined at the time of conception. When the baby is conceived, a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell, determining whether the baby will be genetically female (XX) or male (XY). To be genetically female, one needs to be (XX), whereas to be a genetic male, (XY) is needed. It is the Y chromosome that is essential for the development of the male reproductive organs, and with no Y chromosome, an embryo will develop into a female. This is because of the presence of the sex determining region of the Y chromosome, also known as the SRY gene.

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