Overview of the circadian pattern of gene expression in Arabidopsis thaliana. All expression profiles are grouped into four separate phase classes by correlation to a cosine curve with the same sampling rate (12 points over 2 complete periods). Profiles are then sorted by decreasing autocorrelation with circadian shift. The pattern of two areas of elevated gene expression (red) interspaced by the areas of lowered gene expression (green areas) reflecting two complete cycles over two days of observation is clearly visible throughout entire data. The heatmaps show all transcripts represented on microarray (over 22,000 probesets).