What is the Barr body in the context of X-inactivation?

• A. A gene responsible for determining sex
• B. A structure found in male cells
• C. A protein that initiates X-inactivation
• D. An inactivated X chromosome in a female cell

Answer: (D)

Verified step by step guidance

1. Understand that in humans, females have two X chromosomes (XX) while males have one X and one Y chromosome (XY).
2. Recognize that X-inactivation is a process that occurs in female cells to ensure dosage compensation, meaning that females do not have twice the number of X-linked gene products as males.
3. Learn that during X-inactivation, one of the two X chromosomes in each cell is randomly chosen to be inactivated. This inactivated X chromosome condenses into a compact structure known as a Barr body.
4. Note that the Barr body is typically found in the nucleus of female cells and is not present in male cells, as males have only one X chromosome.
5. Remember that the Barr body is an example of how cells regulate gene expression to maintain balance between the sexes, ensuring that females, like males, have one functional set of X-linked genes.