Figure 1.

Simplified schematic illustrating DSB repair mechanisms induced by CRISPR/Cas9. The three pathways, HDR, NHEJ, and MMEJ, are used for different gene editing purposes. The black triangles indicate locations of the cut site. NHEJ leads to frequent small insertions or deletions that can lead to disruptive frameshift mutations and premature stop codons. This approach is best suited for generating point mutants or knocking out a gene. Both HDR and MMEJ pathways can be used to introduce longer DNA sequences, but they each require an exogenous donor DNA template. These mechanisms are well suited for introducing precise mutations or knocking in an epitope tag or reporter gene, such as green fluorescent protein. Modified from Sakuma et al.,³⁴ with permission.