Fig. 4

Network motifs from tinkering. Motifs are identified as small groups of interacting elements with a well-defined arrangement of links. These links can correspond to physical interactions among proteins or to regulatory links among genes. In this figure, gray balls and links indicate units and their interactions, respectively. Starting from the simplest graph (a), we can generate different motifs by gene duplication (DUP) or link addition (ADD). Three common motifs found in cellular networks are highlighted by the colored boxes. Here DUP, NEW, and DE indicate duplication events, introduction of new links, or their deletion, respectively