This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
"Transition mutation" occurs in 
Select and explain. 
A. A - G, B. A - C, C. A - T, D. D - G
A: A - G
Answer: A: A - G 
Explanation: Replacement of purine by another purine (A to G or G to A ) or pyrimidine by pyrimidine (T to C or C to T ) is called transition mutationRef: DM Vasudevan, 7th edition, page no: 612