Organ system relationships and TF count by organ system. Number of TFs expressed at each stage for the sixteen organ systems. Colored circles show stage range when each organ system becomes detectable and connecting lines show developmental relationships between organ systems. Stage ranges are shown on the bottom line with corresponding developmental time in hours above. The two numbers on the right indicate the total number of TFs (Total) expressed in each organ system and the subset (u) representing TFs that were previously uncharacterized, or uncharacterized in embryonic development. See text for organ system descriptions.