This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Genetics, Subject name: Biochemistry
[{'content': 'Sickle cell anemia is the clinical manifestation of homozygous gene to an abnormal haemoglobin molecule. The event responsible for the mutation in the b chain is: \nSelect and explain. \nA. Insertion, B. Deletion, C. Nondisjunction, D. Point mutation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D Harper, 26th ed, p. 409, Table (40-6) & 25th ed, p. 500, Table (42.6)', 'role': 'assistant'}]