Barr body is seen in :
**Core Concept**
The Barr body is a cytogenetic feature associated with X chromosome inactivation, where one of the two X chromosomes in female mammals is inactivated to avoid dosage compensation. This process is crucial for the proper development and function of female mammals.
**Why the Correct Answer is Right**
Klinefelter's syndrome is a condition characterized by an extra X chromosome in males, resulting in a 47,XXY karyotype. The presence of an extra X chromosome leads to X chromosome inactivation, and the Barr body is a visible representation of this process. In individuals with Klinefelter's syndrome, one of the X chromosomes is inactivated, forming a Barr body. This is in contrast to normal males, who have only one X chromosome and therefore do not form a Barr body. Testicular feminization, also known as androgen insensitivity syndrome, is a condition where individuals are genetically male (46,XY) but have a female phenotype due to resistance to androgens. However, this condition is not associated with the presence of a Barr body.
**Why Each Wrong Option is Incorrect**
* **Option A:** Turner's syndrome is a condition characterized by a missing or partially deleted X chromosome in females, resulting in a 45,X karyotype. Since individuals with Turner's syndrome have only one X chromosome, they do not form a Barr body.
* **Option C:** The correct spelling is "Testicular feminization syndrome," and it is not associated with the presence of a Barr body. Individuals with this condition are genetically male (46,XY) but have a female phenotype due to resistance to androgens.
* **Option D:** Normal males have a 46,XY karyotype and only one X chromosome, which is not inactivated. Therefore, they do not form a Barr body.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the presence of a Barr body can be used as a cytogenetic marker to identify individuals with X chromosome abnormalities, such as Klinefelter's syndrome. This knowledge is crucial in the diagnosis and management of these conditions.
**✓ Correct Answer: B. Klinefelters syndrome**