Describe the determination of sex in humans (XX and XY chromosomes)

Sourav PanNovember 4, 2024

Answered

The determination of sex in humans is primarily governed by the presence of two types of sex chromosomes: X and Y. This system is known as the XY sex-determination system. Here’s how it works:

Sex Chromosomes

1. XX Chromosomes:
   • Females typically have two X chromosomes (XX). Each parent contributes one sex chromosome, with the mother always providing an X chromosome through her egg.
2. XY Chromosomes:
   • Males have one X and one Y chromosome (XY). The father contributes either an X or a Y chromosome through his sperm. If the sperm carries an X chromosome, the resulting offspring will be female (XX); if it carries a Y chromosome, the offspring will be male (XY).

Mechanism of Sex Determination

• The presence of the Y chromosome is crucial for male development. Specifically, the SRY gene (Sex-determining Region Y) located on the Y chromosome acts as a master switch that initiates male sexual development. When the SRY gene is activated, it triggers a cascade of genetic events that lead to the formation of male reproductive structures and the production of male hormones, such as testosterone.
• In the absence of a Y chromosome (i.e., in XX individuals), the default developmental pathway leads to female characteristics. This occurs because there is no SRY gene to initiate male development, allowing for the formation of female reproductive anatomy.

Summary

• XX (Female): Two X chromosomes lead to female development; both X chromosomes are inherited from parents (one from each).
• XY (Male): One X and one Y chromosome lead to male development; the X is inherited from the mother, while the Y is inherited from the father.

Exceptions and Variations

While most individuals fit into these categories, there are exceptions due to various genetic conditions:

• Swyer Syndrome: Individuals with an XY genotype may develop female characteristics due to mutations affecting the SRY gene.
• Klinefelter Syndrome (XXY): Males with an extra X chromosome may have reduced fertility and other physical traits.
• Turner Syndrome (X0): Females with only one X chromosome may experience developmental issues.