The hierarchy of mega-nuclease–induced HDR leading to PGE. PGE is defined as the fraction of HDR leading to the conversion of the desired knock-in mutations using exogenous homology donors. In the PGE products, retrospectively, the hierarchy of the HDR pathway is determined primarily by the types of homology donors and secondarily by the genomic lesions. dsDNA donors containing a sizable central heterology must be converted via the DSBR model, which generates long conversion tracts with a linear distribution. ODN donors can utilize both SDSA and ssDI pathways, depending on the strandedness of the ODNs and the relative position of the knock-in mutation to the genomic lesion. These pathways generate short conversion tracts in normal distributions. SDSA is preferentially utilized in the presence of double-stranded genomic lesions when both pathways can convert the knock-in mutation effectively.
