Saccharomyces cerevisiae YPH499N Genome sequencing

The modern evolutionary synthesis entails that mutations occur at random, independently of the environment in which they confer an advantage. However, there are indications that cells in challenging conditions can rapidly adapt utilizing processes beyond selection of pre-existing genetic variation. Here, we show that a challenging environment can induce mutations independently in many yeast cells in the absence of general mutagenesis. Whole genome sequencing of cell lineages reveals a repertoire of independent mutations within a single lineage that arose only after the cells were exposed to the challenging environment. Other cells in the same lineage adapted without any mutation in their genomes. Thus, our experiments uncovered multiple alternative routes for heritable adaptation that were all invoked in the same lineage during a short period. Our results imply the existence of adaptation mechanisms beyond random mutation, suggesting a tight connection between physiological and genetic processes.