Yeast species tree. We analyzed functional attributes and interactions of genes gained since the whole-genome duplication (red circle) along the path leading to S. cerevisiae. We assigned genes in S. cerevisiae to one of three age groups, pre-WGD, WGD, or post-WGD. The assignment was based on the recent reconstruction of the gene content of an ancestral pre-WGD yeast, which was derived from an analysis of the sequence similarity and synteny of genes in the listed species . An analysis using additional, more specific age groups is presented in Section S2.2 in Additional file 1.