Which chromosomal nondisjunction disorder is caused by the presence of an extra full or partial copy of chromosome 21 (Trisomy 21)?
Answer and explanation
Correct answer: B. Down syndrome
- Step 1: Down syndrome arises when homologous chromosome 21 pairs fail to segregate during gametic meiosis, giving 47 chromosomes. Step 2. It is characterized by intellectual disability, characteristic epicanthic folds, and congenital cardiac anomalies. Answer: Down syndrome. Why not the others: Turner syndrome is 45,X monosomy; Klinefelter syndrome is 47,XXY; Cri-du-chat is a partial deletion on chromosome 5.
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