Targeting approaches for genome editing. NHEJ uses a single guide RNA (green) targeting the protein coding sequence of a gene to disrupt expression by a frameshift mutation (×). Dual guide RNA uses two gRNAs in close proximity to delete the intervening sequences (blue arrow). HDR can be used with either a single-stranded DNA oligonucleotide (ssODN) or a double-stranded DNA donor (plasmid dsDNA) to induce specific mutations.