Down's syndrome is an example of

Options

A. aneuploidy
B. polyteny
C. polyploidy
D. monoploidy

Answer

### Step-by-Step Solution:

1. **Understanding Down's Syndrome**:
- Down's syndrome is a chromosomal disorder characterized by the presence of an extra chromosome. Specifically, individuals with Down's syndrome have three copies of chromosome 21 instead of the usual two. This condition is referred to as trisomy 21.

2. **Identifying Chromosomal Abnormalities**:
- The presence of an extra chromosome indicates an abnormal number of chromosomes in the cells. The typical chromosomal count in humans is 46 (2n), but in Down's syndrome, it is 47 (2n + 1).

3. **Analyzing the Options**:
- The options provided are:
- **Aneuploidy**: This refers to a condition where the number of chromosomes is not an exact multiple of the haploid number, indicating an abnormal count (e.g., 2n - 1, 2n + 1).
- **Polyteny**: This is a condition where chromosomes replicate without separating, resulting in multiple copies of the same chromosome.
- **Polyploidy**: This refers to cells having more than two complete sets of chromosomes (e.g., triploidy, tetraploidy).
- **Monoploidy**: This condition involves having only one set of chromosomes.

4. **Conclusion**:
- Since Down's syndrome is characterized by an abnormal number of chromosomes (specifically, an extra chromosome), it falls under the category of aneuploidy. Therefore, the correct answer is **aneuploidy**.

### Final Answer:
Down's syndrome is an example of **aneuploidy**.

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