**Core Concept**
The Barr body is a compact, inactive X chromosome found in female mammals, including humans, that has undergone X-chromosome inactivation. This process is crucial for dosage compensation to ensure that males and females have equal expression of X-linked genes.

**Why the Correct Answer is Right**
In females, one of the two X chromosomes is randomly inactivated in each cell through a process involving the XIST gene, which coats the inactive X chromosome and prevents its expression. This inactivated X chromosome then condenses into a compact, darkly staining body visible under a microscope. The Barr body is a hallmark of female mammals and serves as a visible indicator of X-chromosome inactivation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because the Barr body is indeed present in females, who have two X chromosomes. The presence of a Barr body in females is a direct result of X-chromosome inactivation.
* **Option B:** Incorrect because the Barr body is not typically associated with males, who have only one X chromosome and therefore do not undergo X-chromosome inactivation.
* **Option C:** Incorrect because this option is incomplete, but generally speaking, the Barr body is indeed present in females with Turner syndrome, who have only one X chromosome.
* **Option D:** Incorrect because this option is also incomplete, but females with Klinefelter syndrome (XXY) would not typically have a Barr body.

**Clinical Pearl / High-Yield Fact**
The presence of a Barr body is a useful diagnostic tool for identifying female mammals, particularly in cases where the sex of the individual is unclear. However, it is essential to note that the Barr body is not present in males or in females with certain chromosomal abnormalities.

**Correct Answer: B. Males do not have a Barr body.**