Genotype of a Down's syndrome is

Options

A. 45 + XX
B. 44 + XY
C. 44 + XXY
D. 22 + XY

Explanation

### Step-by-Step Solution:

1. **Understanding Down Syndrome**: Down syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. This results in a total of 47 chromosomes instead of the normal 46.

2. **Chromosome Count**: In a typical human, there are 46 chromosomes, which consist of 44 autosomes (22 pairs) and 2 sex chromosomes (XX for females and XY for males).

3. **Trisomy Definition**: The term "trisomy" refers to the condition where an individual has three copies of a particular chromosome instead of the usual two. In the case of Down syndrome, there are three copies of chromosome 21.

4. **Genotype Representation**: The genotype of an individual with Down syndrome can be represented as:
- 44 autosomes + 1 extra chromosome 21 (making it 45 total autosomes) + 2 sex chromosomes (which can be XX or XY).
- This can be summarized as 45 + XX or 45 + XY.

5. **Conclusion**: Therefore, the correct genotype representation for Down syndrome is 45 + XX or 45 + XY, indicating the presence of an extra chromosome 21 along with the normal sex chromosomes.

### Final Answer:
The genotype of Down's syndrome is 45 + XX or 45 + XY.

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