Topology of the 100 gene regulatory networks proposed by Mendes. Blue/red edges correspond to activation/inhibition. For the Erdös-Rényi topology (a) each gene is equally likely to be connected to every other gene, while the scale-free topology (b) is characterized by large interaction hubs with many connections.
Margolin et al. BMC Bioinformatics 2006 7(Suppl 1):S7 doi:10.1186/1471-2105-7-S1-S7