## **Core Concept**
Barr bodies are inactive X chromosomes typically found in female mammals, representing a form of dosage compensation to equalize X-linked gene expression between males (XY) and females (XX). The presence of Barr bodies is used as a marker for cells with more than one X chromosome.

## **Why the Correct Answer is Right**
The correct answer, , represents a male karyotype with one X and one Y chromosome. Males have only one X chromosome, which is active, and do not have Barr bodies because they do not have an extra X chromosome to inactivate.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This genotype represents a female with Turner syndrome (45,X) but actually has only one X, however some sources could mislead here; crucially though individuals with more than one X usually show barr bodies; barr bodies are usually associated with more than one X;
- **Option B:** - This genotype represents Klinefelter syndrome (47,XXY), a condition where a male has an extra X chromosome. As a result, one of the X chromosomes is inactivated to form a Barr body.
- **Option C:** - This genotype represents Triple X syndrome (47,XXX), a female with an extra X chromosome. Two of the X chromosomes are inactivated to form Barr bodies.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the number of Barr bodies in a cell is one less than the total number of X chromosomes. For example, a normal female (46,XX) has one Barr body, while a male (46,XY) has none.

## **Correct Answer:** .