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
Patient with HNPCC (hereditary nonpolyposis colon cancer) has genes with microsatellite instability. This is due to failure of which repair mechanism of DNA 
Select and explain. 
A. Mismatch repair, B. Base excision repair, C. Homologous end joining repair, D. Non homologous end joining repair
A: Mismatch repair
Answer: A: Mismatch repair 
Explanation: Mismatch repair: It is one of the repair mechanisms in DNA replication. It operates when there is mismatched base paining. For eg: when A pairs with C. This repair mechanism is defective in HNPCC.