Number of Barr bodies in XXY males is?

**Core Concept**
In humans, the number of Barr bodies (inactivated X-chromosome bodies) in a cell is directly related to the number of X-chromosomes present, as each X-chromosome is inactivated to form a Barr body. This phenomenon is a result of X-chromosome inactivation, a mechanism that ensures dosage compensation between males and females.

**Why the Correct Answer is Right**
In XXY males (Klinefelter syndrome), one of the two X-chromosomes is inactivated to form a Barr body. This results in the presence of one Barr body in each cell. The process of X-chromosome inactivation is mediated by the X-inactive specific transcript (XIST) gene, which coats the inactive X-chromosome and silences its expression. This ensures that the gene expression from the X-chromosome is reduced to half the level of the single X-chromosome in males.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the number of Barr bodies in XXY males. The presence of two X-chromosomes would result in two Barr bodies if both were inactivated, which is not the case in XXY males.
**Option B:** This option is incorrect because it underestimates the number of Barr bodies in XXY males. In XXY males, one Barr body is present due to the inactivation of one X-chromosome.
**Option C:** This option is incorrect because it overestimates the number of Barr bodies in XXY males. While XXY males do have two X-chromosomes, only one is inactivated to form a Barr body.

**Clinical Pearl / High-Yield Fact**
In females (XX), the number of Barr bodies is typically one, due to the inactivation of one X-chromosome. However, in rare cases of X-chromosome abnormalities, such as XXY males, the number of Barr bodies can be altered.

**Correct Answer:** C. One.