Illustration of the distribution of the number of functions that each gene participates in for the TRN of H. sapiens . Each circle represents a TF. The network is divided into six levels using the reachability as the penalty function and placed in relevant levels. The horizontal lines separate the TFs to different levels. The genes are colored according to the number of Gene ontology terms they are annotated with in gray scale. The least number of functions is assigned the color black, where the largest number of functions is assigned the color white.