Trisomy of 21st chromosome results in

Options

A. Down's syndrome
B. Sickle cell anaemia
C. Turner's syndrome
D. Klinefelter's syndrome

Answer

**Step-by-Step Solution:**

1. **Understanding Trisomy**: Trisomy refers to the presence of an extra chromosome in an individual's genetic makeup. In the case of trisomy 21, there is an additional copy of the 21st chromosome.

2. **Identifying the Condition**: The question asks what condition is caused by trisomy of the 21st chromosome. The options provided are Down syndrome, sickle cell anemia, Turner's syndrome, and Klinefelter syndrome.

3. **Analyzing the Options**:
- **Down syndrome**: This condition is indeed caused by trisomy 21, where individuals have three copies of chromosome 21.
- **Sickle cell anemia**: This is an autosomal recessive disorder caused by a mutation in the hemoglobin gene, not related to trisomy.
- **Turner's syndrome**: This condition is caused by the absence of one of the X chromosomes (monosomy X) in females, not related to the 21st chromosome.
- **Klinefelter syndrome**: This condition is caused by the presence of an extra X chromosome in males (XXY), also not related to the 21st chromosome.

4. **Conclusion**: Based on the analysis, the only condition that results from trisomy of the 21st chromosome is Down syndrome.

5. **Final Answer**: Therefore, the correct answer is Down syndrome.

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