This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic and genetic disorders, Subject name: Pediatrics
[{'content': 'Down&;s syndrome most commonly occurs due to \nSelect and explain. \nA. Reciprocal translocation, B. Nondysjunction in maternal meiosis, C. Translocation defect, D. Nondysjunction in paternal meiosis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Down syndrome occurs due to trisomy 21. In 97% of cases it occurs as result of non dysfunction of chromosome during maternal meiosis. Reference : Nelson TB of pediatrics 19th edition pg 402.', 'role': 'assistant'}]