The relative levels of inter-sample variation for all mismatch probes across exon 50 are displayed graphically in Figure 4 . The error bars represent one standard deviation from the mean of the hybridization specificity ratio determined over a running window of 10 bases in each of the 68 samples. Note that the substitution probes show lower inter-sample variability than one base deletion, two base deletion and . Hybridization specificities of mismatch probes. A 10-base running window of the log 10 hybridization specificity ratios of substitution (red), one base deletion (green), two base deletion (blue) and one base insertion (black) was plotted for the sense (A) and antisense (B) strands of ATM exon 50. The light red, light green, light blue and gray shaded areas represent -1 SD of the log 10 hybridization specificity ratios for the substitution, one base deletion, two base deletion and one base insertion probes, respectively. one base insertion probes, in agreement with Table 1 . The variability in hybridization specificity measurements is consistent across all 62 ATM coding exons (Supplementary Figure 1) .