In Down 's syndrome of a male child , the sex complement is

Options

A. XO
B. XY
C. XX
D. XXY

Explanation

To determine the sex complement in Down syndrome for a male child, we need to understand the genetic basis of the condition.

### 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.

2. **Karyotype of Down Syndrome**:
- The normal human karyotype consists of 46 chromosomes, arranged in 23 pairs. In Down syndrome, there is an additional chromosome, making it 47 chromosomes in total.

3. **Sex Complement in Males**:
- Males typically have one X and one Y chromosome, represented as XY. Therefore, in a male with Down syndrome, the karyotype would include the extra chromosome 21.

4. **Karyotype Representation**:
- For a male with Down syndrome, the karyotype can be represented as 47, XY, +21. This indicates that there are 47 total chromosomes, with the sex chromosomes being XY, and an additional chromosome 21.

5. **Choosing the Correct Option**:
- From the options given:
- Option 1: XO (not applicable for males)
- Option 2: XY (correct for males with Down syndrome)
- Option 3: XX (not applicable for males)
- Option 4: XXY (indicative of Klinefelter syndrome, not Down syndrome)
- The correct answer is Option 2: XY.

### Final Answer:
The sex complement in Down syndrome of a male child is **XY**.

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