SRY (Sex-determining Region Y) Gene Role for Gender Identification

Context: Recent studies from Italy and the USA have reported rare cases of biological females carrying the SRY gene, challenging the traditional understanding of sex determination.

What Determines the Sex of a Baby?

• Sex determination is the biological process that decides whether a baby develops as a male or female, influenced by genetic and hormonal factors.
• The sex of a baby is determined by the SRY (Sex-determining Region Y) gene, which is located on the Y chromosome.
• If an embryo has an SRY gene, it develops as a male.
• If the SRY gene is absent, the embryo follows the default female pathway.
• In rare cases, individuals with two X chromosomes (XX) can have the SRY gene and develop male characteristics.

How Does the SRY Gene Work?

• Every human has 23 pairs of chromosomes.
• The first 22 pairs (1-22) are the same in males and females.
• The 23rd pair is the sex chromosomes:
  • Females (XX): Receive one X chromosome from the mother and one X from the father.
  • Males (XY): Receive an X chromosome from the mother and a Y chromosome from the father.

Role of SRY in Male Development

• The Y chromosome contains the SRY gene, which triggers the formation of testes.
• The testes produce testosterone, leading to the development of male sexual characteristics.
• If the SRY gene is non-functional (due to a mutation), an XY embryo develops ovaries instead of testes, becoming a biological female.

SRY Gene in XX Individuals (Rare Cases)

• Rarely, a mutation can transfer the SRY gene from the Y chromosome to the X chromosome. This process is called translocation.
• If a sperm carrying an SRY-positive X chromosome fertilizes an egg, an XX baby is born with the SRY gene.

What Happens to XX Individuals with the SRY Gene?

• Most cases: They develop as males because the SRY gene triggers testis formation. However, these males are sterile since other Y chromosome genes required for sperm production are missing.
• Rare cases: Some XX individuals with the SRY gene develop as biological females.

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