Fig. 1

Evolutionary changes in a hypothetical Gene Regulatory Network (GRN). The consequences of altering an interaction within a GRN can differ enormously, depending on local context. Here, ovals represent genes and arrows represent the activity of that gene product as transcriptional activation (—>) or inhibition ( -|) of another gene. Altering a connection near the beginning of the GRN (red arrow) is more likely to have widespread effects than a connection that involves a single gene at the periphery of the network (blue arrow). Genes encoding regulators near the periphery are in a position to alter functionally related sets of genes in a coordinated manner (gold arrows) that might change a single trait without altering others. Interactions that provide feedback inhibition (purple arrow) or feedback activation can stabilize expression if changes evolve elsewhere in the GRN