Comparison of age related changes in body parts for some biological process. a) For each probeset, we consider the differences in their fold changes between 40-day old and 3-day old flies for the three different conditions (whole body, head or thorax). The mean values for all the probesets associated with certain GO terms corresponding to biological processes were computed and plotted for the three conditions. Note that genes associated with oxidative phosphorylation (GO:0006119) and ATP synthesis (GO:0042773) are more strongly downregulated by age in the thorax (dark gray) than in the head (light gray) or at the whole body level (white). This is not observed for genes related to the TCA cycle (GO:0006121), which behave similarly in the three conditions. In contrast, the genes encoding members of the proteasome complex (GO:0000502) are much more strongly induced by age in the thorax than in the head or at the whole body level, as shown in more detail in b).