What describes X-inactivation in humans?

• A. The process by which one of the two X chromosomes in females is randomly silenced to balance gene expression with males.
• B. The duplication of the X chromosome in males to ensure equal gene dosage with females.
• C. The activation of both X chromosomes in males to match the gene expression levels of females.
• D. The complete deletion of one X chromosome in females to prevent overexpression of X-linked genes.

Answer: (A)

Verified step by step guidance

1. Understand the concept of X-inactivation: In humans, females have two X chromosomes while males have one X and one Y chromosome. To balance the gene expression between males and females, one of the X chromosomes in females is inactivated.
2. Recognize that X-inactivation is a random process: In each cell of a female, one of the two X chromosomes is randomly chosen to be silenced. This ensures that females, like males, have one functional X chromosome per cell.
3. Learn about the mechanism of X-inactivation: The inactivated X chromosome becomes a Barr body, which is a dense structure in the nucleus. This process involves modifications to the DNA and histones, leading to the silencing of gene expression on that chromosome.
4. Consider the implications of X-inactivation: This process prevents females from having double the gene dosage of X-linked genes compared to males, maintaining balanced gene expression across sexes.
5. Differentiate X-inactivation from other processes: It is not the duplication of the X chromosome in males, activation of both X chromosomes in males, or deletion of one X chromosome in females. It specifically involves the silencing of one X chromosome in females.