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: Medicine
Mutation in sickle cell disease is a 
Select and explain. 
A. Silence mutation, B. Missense mutation, C. Nonsense mutation, D. Frame shift mutation
B: Missense mutation
Answer: B: Missense mutation 
Explanation: It is a point mutation at the 6th code of β globin chain leading to substitution of glutamine by valine.