This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics of Common Disorders, Subject name: Pediatrics
[{'content': 'Down syndrome is due to non-disjunction of - \nSelect and explain. \nA. 21, B. 18, C. 11, D. 15', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., 21 Chromosome In 95% of cases of Down syndrome-trisomy of 21:-o Extra chromosome is of maternal in origin.o 1% have mosaic with some all have 46 chromosome,o 4% have robertsonian translocation,o t (13 : 21)o t (14 : 21)o t (15 : 21)o Very rarely long arm of chromosome 21 is triplicate (Partial trisomy).", 'role': 'assistant'}]