Absence of one sex chromosome causes

Options

A. Turner's syndrome
B. Klinefelter's syndrome
C. Down's syndrome
D. Tay-Sach's syndrome

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the condition caused by the absence of one sex chromosome. We need to identify which syndrome is associated with this genetic anomaly.

2. **Identifying the Syndromes**: The options provided are:
- Turner's syndrome
- Klinefelter's syndrome
- Down syndrome
- Tay-Sachs syndrome

3. **Analyzing Turner's Syndrome**:
- Turner's syndrome is a genetic condition that affects females and is characterized by the absence of one of the two X chromosomes (45,X instead of the typical 46,XX).
- It is caused by a phenomenon known as non-disjunction, where the sex chromosomes fail to separate properly during the formation of the egg or sperm.

4. **Analyzing Klinefelter's Syndrome**:
- Klinefelter's syndrome occurs in males and is caused by the presence of an extra X chromosome (47,XXY). This is not related to the absence of a chromosome.

5. **Analyzing Down Syndrome**:
- Down syndrome is caused by the presence of an extra copy of chromosome 21 (trisomy 21), which is unrelated to sex chromosomes.

6. **Analyzing Tay-Sachs Syndrome**:
- Tay-Sachs syndrome is a genetic disorder caused by the absence of a specific enzyme that breaks down fatty substances. It is not related to sex chromosomes.

7. **Conclusion**: Based on the analysis, the only condition that is caused by the absence of one sex chromosome is Turner's syndrome. Therefore, the correct answer is Turner's syndrome.

### Final Answer:
The absence of one sex chromosome causes Turner's syndrome.

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