alleryDown syndrome is most commonly caused by:
AA monosomy of chromosome 21 (only one copy)
BA trisomy of chromosome 21 (three copies)
CTranslocation of chromosome 14
DDeletion of chromosome 5p
Answer & Solution
Correct answer: B. A trisomy of chromosome 21 (three copies)
Down syndrome = Trisomy 21 (3 copies of chromosome 21 instead of 2).
Caused by non-disjunction during meiosis, more common with maternal age.
**Features:** flat face, short stature, intellectual disability.
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