Lyonization can convert one form of these structures into a Barr body.

• A. X chromosome
• B. Y chromosome
• C. Autosomes
• D. Mitochondria

Answer: (A)

Lyonization is X-chromosome inactivation in female mammals. To balance gene expression between males (one X) and females (two Xs), one X chromosome in each cell is largely silenced. The silenced X condenses into a dense, inactive form called a Barr body, typically located near the nuclear envelope. This targeted silencing happens specifically to the X chromosome, not to the Y chromosome, autosomes, or mitochondria, which don’t form Barr bodies. So lyonization converts an X chromosome into a Barr body, explaining the mosaic pattern of X-linked gene expression in females.