Figure 1.

Classes of designer nucleases and gene-editing outcomes. Targeted double-strand breaks can be induced using ZFNs, TALENs, or CRISPR/Cas9. DNA breaks are repaired via endogenous repair pathways such as non-homologous end joining (NHEJ) and homologous recombination (HR). The NHEJ pathway results in short deletions or insertions at the target site that can result in a targeted gene knock-out. The HR pathway is a high fidelity pathway that uses the sister chromatid as a template to correct the DNA break. An exogenous DNA template may be provided for homology directed repair (HDR). This pathway can be exploited to repair mutations or modify DNA at the resolution of a single nucleotide.