FIG. 11.

Fragility of a four-node reduced version of the Human Gonadal Sex Determination model of [48]. Panel A depicts the interaction network. Each node symbol contains the update function of the node. Blue edges ending in filled circles indicate positive regulation, and red edges ending in open circles denote negative regulation. Panel B shows the state transition graph under the synchronous update. Attractor states are indicated by thick borders. The basin of attraction of each attractor is highlighted by the same color as the attractor. State transitions are shown with black arrows, and orange double-sided arrows indicate state pairs that are related by single-node perturbations. These are the transitions that can arise from single-node perturbations and that lead to different long-term behavior than is observed without perturbation. The thickness of each orange edge indicates the Hamming distance between the corresponding attractors. Panel C shows how to calculate the fragility of this reduced model exactly using the information in panel B.