Fig. 2
From: CRISPR/Cas9: the Jedi against the dark empire of diseases
Comparison of NHEJ and HDR. The double-stranded breaks induced by nucleases can be joined by either homologous end joining or homologous directed repair. (a) The NHEJ mediated repair results in gene knockout without any donor DNA. (b) When donor DNA is available,it is cut by the nuclease simultaneously resulting in compatible overhangs; hence gene insertion may also take place by NHEJ. (c) HDR in the presence of donor DNA can be used for precise nucleotide substitutions resulting in modified genes. (d) HDR can also result in gene insertion