CRISPR/Cas9 complexes target specific genomic sequences to create double strand breaks adjacent to the PAM site. b The error-prone non-homologous end-joining (NHEJ) DSB repair pathway can be harnessed by CRISPR/Cas9 to introduce pre-mature stop codons in the coding sequence of a gene. c Homologous recombination (HR) is a less efficient, but useful pathway for repairing DSBs in the presence of a DNA template so that precise genome editing can be achieved