Fig. 6
Possible model of NCO mismatch repair pathway choice. NCO repair pathways such as Synthesis-Dependent Strand Annealing (SDSA) form heteroduplex DNA between the recipient homologue’s original sequence (blue) and a small tract of DNA copied from the donor homologue (red). Any mismatching bases must be resolved either by restoring to the recipient allele or converting to the donor allele; only the latter can be detected in offspring. Three possible NCO heteroduplex tracts are depicted, differing in the number and type of mismatch sites (these regions are illustrated as unwound for visual aid purposes only). In all cases, one proposed mismatch repair mechanism (orange arrow) converts site(s) on the recipient chromosome in a donor-strand-biased manner to the allele of the donor chromosome (red). However, in the particular case shown in the middle column—where there is a single mismatch site and the recipient chromosome contains a Strong (S = G or C), not Weak (W = A or T), allele—a different proposed repair mechanism (blue arrow) operates ~53% of the time and restores the G/C recipient allele in a recipient-strand-biased manner, resulting in no observable gene conversions at that site (Supplementary Fig. 8 and Supplementary Note 7). The sum of these two effects can explain the overall 68% bias of observed gene conversions towards G/C
