EMS treatment increased the frequency of cells with extreme YFP fluorescence.

<p>(A) The relationship between “forward scatter” (“FSC”, a proxy for cell size) and YFP fluorescence is shown for a population of control cells. FSC and YFP fluorescence are both reported in arbitrary units on a log scale. A similar linear relationship was observed for other genotypes. Approximately 2% of flow cytometry “events” had YFP fluorescence less than the range plotted and are not shown. The fluorescence phenotype of each sample in the secondary screen was calculated as the median YFP/FSC ratio for FACS events with FSC values between 5.30 and 5.55 (indicated with dotted lines). (B) The distribution of YFP fluorescence phenotypes is shown for EMS-treated (dashed curve) and control cells (solid curve) from one of the nine replicate populations of EMS-treated and control cells analyzed in the primary screen. Locations of the 1st, 5th, 95th, and 99th percentiles of the control sub-population are indicated, and vertical dashed lines show the average thresholds used for cell sorting (see also <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002497#pgen.1002497.s003" target="_blank">Table S1</a>). (C) The difference between the number of EMS-treated and control cells in the population is plotted for a range of fluorescence levels (grey line). The black curve shows a spline fit to these data. Positive values indicate fluorescence phenotypes that were more abundant in the EMS-treated sample, whereas negative values indicate fluorescence phenotypes that were more abundant in the control sample. The spline crosses zero at approximately the 17th and 84th percentiles of the control population. The percentage of the EMS-treated population that is either over or under represented is shown for the following percentile ranges: 1–17, 17–84, 84–99. The X-axis representing YFP fluorescence levels has the same scale as in panel B.