Consistent with the first MEP strain examined above, we observed a significant increase in total LOH events at MET15 in populations of aging UCC5185 cells (Figure 2B). By 45 hours, when populations have passed their median viability, median LOH rates were increased 2-fold compared to the rate observed in the young population (Figure 2B) (p<0.0001, Fisher's exact test based on contingency tables). Between 70 and 95 hours, when population viability had fallen below ∼10%, median LOH rates were increased by four to eight-fold (p<0.0001, Fisher's exact test based on contingency tables). We found both reciprocal and non-reciprocal events increased with similar kinetics in aging populations (Figure 2C), indicating that cells maintain a stable ratio of these events throughout the aging process. This result suggests that aging cells may experience an increased frequency of DNA damage within the rDNA array, rather than an age-associated defect in a particular repair pathway.
