Question

Sol.(c) [Key Concept: Down's Syndrome — Trisomy 21] Down's syndrome is due to THREE COPIES OF CHROMOSOME 21 (trisomy 21). Non-disjunction of chromosome 21 during meiosis produces an egg or sperm with two copies; fertilisation results in 47 chromosomes with 3 copies of chromosome 21. Features: intellectual disability, characteristic flat facial features, epicanthal folds, single palmar crease, and congenital heart defects in 40% of cases.