This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
In sickle cell anaemia, the mutational event responsible for the mutation for beta chain is - 
Select and explain. 
A. Crossing over, B. Point mutation, C. Inseion, D. Deletion
B: Point mutation
Answer: B: Point mutation 
Explanation: In sickle cell disease there is single nucleotide change in the B globin gene leading to substitution of valine for glutamate at position 6 of the B globin chain, this is point mutation. Ref:Postgraduate Hematology by Victor Hoffbrand pg :109