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
CRISPR - Cas9 mediated gene editing involves which DNA repair mechanism 
Select and explain. 
A. Nucleotide excision repair, B. Mismatch repair, C. Base excision repair, D. Non Homologous End joining repair
D: Non Homologous End joining repair
Answer: D: Non Homologous End joining repair 
Explanation: CRISPR - Cas9 involves both homologous and non homologous end joining repair mechanism.