**Core Concept**
The Barr body is a structure found in the cell nucleus that represents an inactive X chromosome in female mammals. It is a result of X-chromosome inactivation, a process that ensures dosage compensation between males and females, who have one X and one Y chromosome, respectively.

**Why the Correct Answer is Right**
The Barr body was first detected by Murray Barr in 1949 in neurons of the spinal cord. This discovery was significant as it provided evidence for the presence of inactive X chromosomes in female mammals. The Barr body is typically found in the nucleus of female cells, where it represents the inactivated X chromosome. This process of X-chromosome inactivation occurs early in embryonic development and ensures that females have the same level of gene expression as males, who have only one X chromosome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the Barr body was not first detected in the 1920s, and there is no evidence to suggest that it was discovered by a scientist other than Murray Barr.
**Option B:** This option is incorrect as the Barr body is not a feature of the Y chromosome, but rather an inactive X chromosome found in female cells.
**Option C:** This option is incorrect as the Barr body was not first detected in the 1950s, but rather in 1949.

**Clinical Pearl / High-Yield Fact**
The Barr body is a useful marker for sex chromosome abnormalities, such as Turner syndrome, where a female has only one X chromosome. The presence of a Barr body can also be used to distinguish between female and male cells in forensic medicine.

**Correct Answer:** C. 1949