The structure and dynamics of the gap gene network. (a) Nested feedback loops with two different kinds of regulations. Different kinds of regulations generate precise spatial expressions and permit shared spatial expressions. (b) Gene regulatory network of gap genes. This figure shows that the gap genes are activated or repressed by maternal genes, and are expressed in two broad domains (bcd and cad domain) along the AP axis (Jaeger 2009). (c) Conceptual illustration of an attractor. Dynamic trajectories of the gene states (red nodes) flow to the fixed point attractor (yellow node). (d) Spatial distribution of the five participating gap genes along the anterior-posterior (AP) axis (where 0% EL is the anterior pole), with gap genes plotted separately. The attractors are represented by dotted lines in 50, 60, 70 and 90% EL, respectively.