Genes of low regulatory complexity are common and genes of high regulatory complexity are rare in D. melanogaster and C. elegans. Distribution of genes with respect to complexity of expression in (a) FlyBase index (FBx), (b) BDGP in situ hybridization index (BDGPx), and (c) WormBase index (WBx). In all three cases, the distributions are heavily weighted toward genes expressed in a small number of locations and show relatively few genes deployed in a large number of tissues.
Nelson et al. Genome Biology 2004 5:R25