Sexual differentiation

Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote. As male and female individuals develop from zygotes into fetuses, into infants, children, adolescents, and eventually into adults, these differences become more pronounced.

Overview

Sexual differentiation starts with the XY sex-determination system that is present in humans, and complex mechanisms that interpret these chromosomal variables into gonadal sex. This is followed by the differentiation of the gonads into either testes or ovaries, depending on the presence of specific factors. These factors also control the development of the internal and external genitalia, leading to the differences between males and females.

Genetic Determination of Sex

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females typically have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males typically have two distinct sex chromosomes (XY), and are called the heterogametic sex.

Gonadal Differentiation

Gonadal differentiation is the process of development of the gonads into either testes (in males) or ovaries (in females). The development into testes is triggered by the SRY gene, which is normally found on the Y chromosome. The development into ovaries is currently thought to be triggered by the lack of the SRY gene.

Development of Genitalia

The development of the genitalia is a part of sexual differentiation and is directed by the gonads. The internal genitalia are derived from the same embryonic structures in males and females, and their final forms are determined by hormones produced by the gonads. The external genitalia are also derived from the same embryonic structures, and their development is also directed by hormones.

Disorders of Sexual Differentiation

Disorders of sexual differentiation (DSDs) are medical conditions involving the development of the sexual organs and/or the sex chromosomes. They can involve abnormalities in the number or structure of the sex chromosomes, the development of the gonads, or the development of the genitalia.

See Also

• XY sex-determination system
• Disorders of sexual differentiation
• Gonadal differentiation
• Development of genitalia

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  Y Chromosome Showing SRY