Figure 7
From: Threshold-dominated regulation hides genetic variation in gene expression networks
In the case of very steep sigmoids, the (μ1, μ2) space of Model 2 is divided into 5 domains, each domain comprising the parameter values giving a particular type of SSP. For example, in the domain denoted (Z1, 1), x1 is at its threshold and is singular, thus Z1 ≠0, 1, while x2 is above its threshold, thus Z2 = 1. Only in the shaded domain are both variables singular and actively regulating. For steep, but not infinitely steep response functions the relations are approximately true.