The Saccharomyces cerevisiae genome sequence, augmented by new data on gene expression and function, continues to yield new findings about eukaryote genome evolution. Analysis of the duplicate gene pairs formed by whole-genome duplication indicates that selection for increased levels of gene expression was a significant factor determining which genes were retained as duplicates and which were returned to a single-copy state, possibly in addition to selection for novel gene functions. Proteome comparisons between worm and yeast show that genes for core metabolic processes are shared among eukaryotes and unchanging in function, while comparisons between different yeast species identify 'orphan' genes as the most rapidly evolving fraction of the proteome. Natural hybridisation among yeast species is frequent, but its long-term evolutionary significance is unknown.