Genetic defect in Klinefelter’s syndrome?
**Core Concept**
Klinefelter's syndrome is a genetic disorder characterized by the presence of an extra X chromosome in males, leading to various physical and developmental abnormalities.
**Why the Correct Answer is Right**
The genetic defect in Klinefelter's syndrome involves the presence of an extra X chromosome, resulting in a 47,XXY karyotype. This extra X chromosome disrupts the normal balance of sex chromosomes, leading to impaired testicular function, infertility, and other clinical manifestations. The extra X chromosome also affects the expression of genes involved in testicular development and function, contributing to the syndrome's characteristic features.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the genetic defect in Klinefelter's syndrome. The presence of an extra Y chromosome is not associated with this condition.
**Option B:** This option is incorrect because it suggests that Klinefelter's syndrome is caused by a defect in the Y chromosome, which is not the case. The syndrome is characterized by an extra X chromosome, not a Y chromosome anomaly.
**Option C:** This option is incorrect because it proposes a different genetic mechanism for Klinefelter's syndrome. The syndrome is not caused by a deletion or mutation of the X or Y chromosome, but rather by the presence of an extra X chromosome.
**Clinical Pearl / High-Yield Fact**
Klinefelter's syndrome is the most common sex chromosome disorder in males, affecting approximately 1 in 650 live births. It is essential to recognize the characteristic features of this syndrome, including tall stature, gynecomastia, and infertility, to provide appropriate medical care and counseling.
**Correct Answer: D. Presence of an extra X chromosome.**