Fig. 1.

The (simplified) gene regulatory network controlling primary sex determination in placental mammals (see Additional file 1: Figure S1 for the more complete network). Ellipsoids and rectangles represent Boolean and multi-valued variables, respectively. Black nodes correspond to inputs. Normal green and blunt red arrows represent positive and negative interactions, respectively. Y stands for Y chromosome, which contains the gene Sry; AS stands for the developmental signal that allows Sry activation; AF stands for the developmental signal that activates Foxl2; and IW stands for the developmental signal that inhibits the Wnt4 signalling pathway; b-cat stands for ß-catenin. Description of these temporal signals is provided in the Additional file