Kinefelter's syndrome is due to:

Options

A. One X and two Y
B. Two X and one Y
C. One X only
D. One Y only

Answer

**Step-by-Step Solution:**

1. **Understanding Klinefelter's Syndrome**: Klinefelter's syndrome is a genetic condition that affects males and is characterized by the presence of an extra X chromosome.

2. **Chromosomal Composition**: Normally, males have one X and one Y chromosome (XY). In Klinefelter's syndrome, the chromosomal composition changes to 47 chromosomes, specifically 44 autosomes, 2 X chromosomes, and 1 Y chromosome (XXY).

3. **Identifying the Cause**: The extra X chromosome in Klinefelter's syndrome is a result of nondisjunction during meiosis, where chromosomes fail to separate properly, leading to gametes with an abnormal number of chromosomes.

4. **Analyzing the Options**:
- Option A: 1X and 2Y - Incorrect, as this does not represent Klinefelter's syndrome.
- Option B: 2X and 1Y - Correct, as this matches the XXY configuration of Klinefelter's syndrome.
- Option C: 1X only - Incorrect, as this does not reflect the condition.
- Option D: 1Y only - Incorrect, as this does not reflect the condition.

5. **Conclusion**: The correct answer is Option B: 2X and 1Y, which accurately describes the chromosomal makeup of individuals with Klinefelter's syndrome.