X inactivation

Definition

X inactivation is the process by which one of the two X chromosomes in female mammals is randomly silenced to balance gene expression between males and females. This ensures that females, like males, have one functional copy of the X chromosome in each cell.

5 Must Know Facts For Your Next Test

1. X inactivation occurs early in embryonic development, typically around the blastocyst stage.
2. The inactive X chromosome forms a structure known as a Barr body.
3. X inactivation is random; either the maternal or paternal X chromosome can be silenced.
4. Once an X chromosome is inactivated in a cell, all descendant cells maintain that same inactive state.
5. X-linked recessive disorders can manifest differently depending on which X chromosome is inactivated.

Review Questions

• What is the purpose of X inactivation?
• At what stage of development does X inactivation typically occur?
• How does X inactivation contribute to genetic diversity within female mammals?

Related terms

Barr Body: A dense, inactive form of an X chromosome found in female cells.

Dosage Compensation: The mechanism that balances the dose of X-linked genes between males and females.

Lyon Hypothesis: The theory proposing that one of the two X chromosomes present in female mammals is randomly and permanently inactivated during early embryonic development.