Statistical Analysis The frequency distribution of cell division time asymmetry index was highly skewed in all the lineages. The trends in means and medians were similar. Ideally medians are preferred over means in skewed distributions. However since outliers in our data, which are old cells are central to the hypothesis being tested, we used means wherever important. Although the experiment had a factorial design, owing to the skewness of the data ANOVA could not be performed. We therefore relied on pair wise comparisons using nonparametric tools. Mann-Whitney test was used for comparison of asymmetry indices of any two lineages. For correlation analysis nonparametric Kendall’s tau was used. Supporting Information Table S1 Statistical analysis of index of cell division time asymmetry is given. Found at: doi:10.1371/journal.pone.0014516.s001 (0.05 MB DOC) Dataset S1 Raw data on cell division time asymmetry indices. References 1. 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