Figure 3.
Two different gRNAs (#1 and #2) bind in a particular genomic region. When gRNA #1 and #2 are coexpressed with a Cas9 nickase, single-strand nicks are created in the DNA at (a), (b), and (c). The nick created at (a) is quickly repaired by HDR using the intact compliment strand as a template and no change occurs. The nicks at (b) and (c) are in close proximity (and on opposite strands) and together behave as a DSB.