Question

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

• A. XY
• B. XO
• C. XX
• D. XXY

Answer 1

The correct option is A

XY

The correct option is A:

Explanation of the correct answer:

1. Down's syndrome occurs due to the presence of an additional copy of chromosome 21 which results in trisomy of chromosome 21.
2. It does not affect the sex chromosomes.
3. Hence, a male child with Down's syndrome will have normal sex chromosomes - XY.

Explanation of the incorrect options:

Option B:

1. XO chromosome abnormality is indicative of Turner's syndrome wherein females have a missing X chromosome.

Option C:

1. XX is the normal sex complement for a human female.

Option D:

1. XXY is indicative of Klinefelter's syndrome wherein a male is born with an extra sex chromosome.

Final answer: The sex complement is XY in Down's syndrome of a male child.