Turner's syndrome is due to

Options

A. Trisomy of chromosome 21
B. Trisomy of chromosome 18
C. Autosomal recessive gene
D. Absence of one sex chromosome

Answer

### Step-by-Step Solution:

1. **Understanding Turner's Syndrome**:
- Turner's syndrome is a genetic condition that affects females. It is characterized by the absence or structural abnormalities of one of the X chromosomes.

2. **Identifying the Cause**:
- Turner's syndrome is classified as a monosomic disorder. Monosomy refers to the presence of only one chromosome from a pair, which means that in Turner's syndrome, one of the X chromosomes is missing.

3. **Chromosomal Composition in Females**:
- Normally, human females have two X chromosomes (XX). In the case of Turner's syndrome, one of these X chromosomes is absent or partially missing, leading to a total of one X chromosome (X0).

4. **Differentiating from Other Conditions**:
- The question provides options that include trisomy of chromosomes 21 and 18, which are associated with Down syndrome and Edwards syndrome, respectively. These conditions involve the presence of an extra chromosome, not the absence of one.
- Additionally, the mention of an autosomal recessive gene is incorrect because Turner's syndrome is a sex-linked disorder, not an autosomal one.

5. **Conclusion**:
- Therefore, the correct answer to the question "Turner's syndrome is due to" is the absence of one sex chromosome.

### Final Answer:
Turner's syndrome is due to the absence of one sex chromosome.

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