Mapping of regulatory space to functional space. a. GAL networks connecting the ancestor and intermediates to S. cerevisiae. Boxed numbers correspond to the network configurations in Table 2. Arrows indicate the connections between networks resulting from the possible evolutionary changes at each intermediate. Two example paths are shown. Red arrows indicate the sequence: specialization of GAL3, specialization of GAL1, loss of GAL4 duplicate, loss of GAL2 duplicate, loss of GAL80 duplicate; green arrows indicate the sequence: specialization of GAL1, loss of GAL2 duplicate, loss of GAL80 duplicate, specialization of GAL3, loss of GAL4 duplicate. The blue arrow indicates the WGD. b. Functional space of GAL network operation showing three network features. More galactokinase (Gal1p, Gal1/3p) molecules in high galactose (+ gal) indicate higher induction strength. Less galactokinase and co-inducer (Gal3p, Gal1/3p) molecules in very low galactose (- gal) indicate better repression strength and switch effectiveness respectively. Black spheres are intermediate GAL networks. S. cerevisiae and the pre- and post- WGD ancestors are indicated by colored squares. Red, green, and blue arrows indicate the evolutionary changes from Figure 3a.