Yeast Hybrids and Polyploids as Models in Evolutionary Studies

In this chapter, we focus on budding yeasts, a group of related species, with fully sequenced genomes. Haploids and diploids from these species can propagate asexually or mate to produce hybrids and polyploids. There are no zygotic barriers among budding yeasts. Thus, interspecific hybrids and polyploid yeasts are widespread in nature or in domesticated strains used for the making of wine, beer, cider, biofuel, and bread. This, together with all the advantages of being fast-growing unicellular organisms, makes yeasts ideally suited for contributing to the understanding of evolution in hybrids and polyploids. We describe the insights gained from the analysis of the ancient whole-genome duplication that occurred in yeast approximately 100 million years ago. Namely, we summarize lessons from the nonrandom retention of duplicated loci in the context of sub- and neofunctionalization of genes and of networks of genes and proteins. We discuss how experimental analysis of yeast evolution (a unique feature in the field of polyploidy research) has contributed to the debate on haploid versus diploid polyploid superiority, showing the complexity of the issue. We show how yeast hybrids have been used as tools to study the mechanisms of divergence between species with regard to gene expression, nucleosome occupancy, DNA replication, and RNA stability. Finally, we discuss the challenges and open questions in this field. This edition first published 2013