alleryDown syndrome in humans is caused by
Amonosomy of chromosome 21
Bdeletion in chromosome 5
Cmutation in HBB gene
Dtrisomy of chromosome 21
Answer & Solution
Correct answer: D. trisomy of chromosome 21
1. Down syndrome arises when an individual receives an extra copy of chromosome 21.
2. Karyotype shows 47 chromosomes with three copies of 21 (trisomy 21).
3. It results from non-disjunction during meiosis, typically in the maternal egg.
_Source: Maharashtra Balbharati Std XII Biology, Ch 3 "Inheritance and Variation" §3.10_
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