“…Repair may be via the non-homologous end joining (NHEJ) pathway [ 65 ], leading to insertions and/or deletions (indels) at the target site. Alternatively, the activity of homology-directed repair (HDR) pathways can facilitate precise genome editing by introducing alternative sequences via a supplied donor DNA ( Figure 3 a) [ 66 , 67 ]. While the initial efficiency of specific targeting, especially when trying to introduce mutations or tags, was initially low and variable [ 68 , 69 ], various improved systems have been developed.…”