Figure 1.

The (simplified) gene regulatory network controlling chicken primary sex determination (see electronic supplementary material, figure S1 for the complete network). Normal green and blunt red arrows represent positive and negative interactions, respectively, and dashed arrows indicate indirect or proposed interactions. Z1 and Z2 represent each a Z chromosome, whereas W represents a W chromosome; the sex chromosome constitution (ZW or ZZ) is thus specified by an adequate combination of these input components.