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: Biochemistry
Sickle cell anemia is the clinical manifestation of homozygous genes for an abnormal haemoglobin molecule. The event responsible for the mutation in the B chain is - 
Select and explain. 
A. Inseion, B. Deletion, C. Non disj unction, D. Point mutation
D: Point mutation
Answer: D: Point mutation 
Explanation: D i.e. point mutation