Fig. 1

Pathways of repair after nuclease cleavage. In a cell with many chromosomes, a unique site on one chromosome is targeted for cleavage by a programmable nuclease (red ‘lightning bolt’). Cells repair the break either by non-homologous end joining (NHEJ), which can leave small insertions or deletions (indels), or homology-dependent repair (HDR) using a template supplied by the experimenter. Although mitotic chromosomes are illustrated here, it is unlikely that these processes occur specifically in mitosis