This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'A Down syndrome child is mentally retarded. All cytogenetic abnormalities may occurs except? \nSelect and explain. \nA. Deleted 21, B. Trisomy 21, C. Robesonia translocation, D. Mosaic', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans is 'a' i.e., Deleted 21", 'role': 'assistant'}]