SUPERSTOCK Resea R ch highlights Nature Reviews Genetics | ao P, published online 2 March 2010; doi:10.1038/nrg2770 Ev OL ut ION Multiple alleles can be maintained in is conserved in the close yeast relative in the presence of galactose and, the gene pool of a population by bal- Saccharomyces kudriavezii, but it was conversely, functional alleles are at ancing selection (in response to local thought to be non-functional in this a disadvantage in backgrounds in adaptations, for example). Hittinger species. To their surprise, Hittinger which only partial gene networks are et al. now show that balancing and colleagues found that whereas constitutively expressed. selection also operates at the level of the Japanese strains of S. kudriavezii Ways in which alternative allelic whole gene-networks. In the example have indeed lost functionality, states could be maintained at studied, the well-characterized Portuguese strains have retained it. multiple loci have been described galactose (GAL) gene network in Having verified that they were previously and include tight linkage, yeast is maintained in alternative still dealing with a single spe- chromosomal inversions, reduced genetic states within a species, cies, the authors showed that this gene flow and inbreeding. With this a phenomenon the authors call a functional polymorphism is very study, Hittinger et al. have added ‘balanced unlinked gene network old indeed — about 89% as old as a new mechanism to this list and polymorphism’ (BuGNP). the species itself. Importantly, the argue that, given the many examples Saccharomyces cerevisiae authors showed both recent and of...