of crude, PCR-amplified DNA from P4 (Figure 2B) had no evidence for reverted c.217_218 delGA. If 33% of the DNA were indeed previously reverted, the mutated allele at c.217_218 delGA should constitute only 33% of the P4 mixed traces in Figure 2B instead of the 50% expected if the culture were entirely ATM−/−, and this is nearly impossible to judge from a non-quantitative sequence trace. The most parsimonious interpretation is that reversion occurred early after reprogramming in the cluster C iPSC of Q3SC, possibly when this cluster was present as a single cell.
