PM- and MM-probe intensities of four selected probe sets before (t = 0) and after (t = 17) washing: Each probe set contains eleven PM and MM probes. Washing affects the different probes in a selective fashion. For example, the high-intensity PM-probes a and b (see labels in the figure) remain nearly unaffected, wheras the weak-intensity probes c and d respond strongly to washing. The horizontal dashed lines are the mean intensities which are log-averaged over all eleven probes of each probe set. The figure shows probes with relatively large set-averaged intensities which are predominantly hybridized with specific transcripts. The sequences of the four labeled probes (a-d) are explicitly given together with the total number of adenines, cytosines, guanines and thymines per sequence. Note that there are no obvious correlations between the given sequences and the intensity changes owing to washing.