How Can Modular Gene Networks Help Evolve New Complex Traits?
We believe that for gene network co-option to occur the organism must have previously evolved modular gene networks. According to [5], a gene network consists of two or more linked gene regulatory circuits, which in turn consist of a signaling pathway (e.g., the wingless signaling pathway) that targets a particular gene. A modular gene network, on the other hand, is a network that behaves in an integrated and context-independent fashion during development [20]. Currently there is no knowledge regarding the size of these modular networks and how common they are in developmental networks, but we will exemplify the concept of modularity with a simple network consisting of two linked gene circuits (X activating Y, and Y activating Z, via their respective signal transduction pathways). The following simplified scheme omits the signal transduction elements: gene X, activated by a CRE in a particular developmental context, produces a protein that activates gene Y by binding to a CRE in Y, whi
