Figure 11

Distribution of viable parameter points in the k ₁₁ k ₁₂ plane. (a) proportion of viable parameter points found through Monte Carlo integration in every bin of the k₁₁ k₁₂ plane. The highest density of viable parameter points appears in configurations for which k₁₁ and k₁₂ are high; that is, model architectures in which both feedback loops are present (although one of them may not be essential). (b) proportion of viable parameter points which define architectures based on a negative feedback loop as a function of k₁₁; that is, as a function of the single parameter that controls the strength of the positive feedback loop. The mean value of the parameter k₁₁ is significantly higher (p-value = 2.0 · 10^-27 Wilcoxon signed rank test) than the centre of the interval in which k₁₁ is defined. The density of viable parameter points increases with the value of the parameter k₁₁.