A Barr body is:

• A. An inactive Y chromosome.
• B. An active X chromosome.
• C. An inactive X chromosome.
• D. An active Y chromosome.

Answer: (C)

Verified step by step guidance

1. Understand that a Barr body is related to the X chromosome in females. In humans, females have two X chromosomes, while males have one X and one Y chromosome.
2. Recognize that in females, one of the X chromosomes becomes inactive to balance the dosage of X-linked genes between males and females. This process is known as X-inactivation.
3. The inactive X chromosome condenses into a structure known as a Barr body. This is a normal process in female cells to ensure that only one X chromosome is active.
4. Remember that the Barr body is not an active chromosome; it is the inactivated X chromosome. This is a key point in understanding the concept of dosage compensation in genetics.
5. Therefore, the correct description of a Barr body is 'an inactive X chromosome.' This helps maintain genetic balance between males and females.