alleryDown's syndrome results from an extra copy of chromosome:
A21
B12
C18
D13
Answer & Solution
Correct answer: A. 21
1. The disorder is caused by a gain of a chromosome.
2. Down's syndrome results in the gain of an extra copy of chromosome 21.
3. So the correct answer is 21.
_Source: syllabus Biology, Ch 5 'Principles of Inheritance and Variation'_
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