- An important goal of evolutionary biology is to identify the genetic mechanisms underlying phenotypes in organisms. Understanding adaptation to osmotic stress has many applications, since this stress affects almost all organisms on Earth. By studying the model organism Saccharomyces cerevisiae using experimental evolution, we can learn about genetic mechanisms driving adaptation to an osmotically stressful environment. I worked with three replicate populations of a Wine/European strain of S. cerevisiae that had adapted to osmotic stress in the laboratory for 750 generations. Seven mutations were identified in these evolved populations as candidates for adaptive alleles and were the subject of my experiment. I subjected cells from the ancestral and evolved strains to evolution experiments that competed their genotypes. I hypothesized that if these mutations were indeed beneficial in an osmotic stress environment, then they would increase in frequency in these experiments. My results showed either no significant change in allelic frequencies or an increase in the ancestor allele. I conclude that while these mutations may have been beneficial in the past environment, they are not advantageous in the yeast populations I studied. This could be due to my experimental design and/or due to the complexity of osmotic stress resistance in yeast.
- Key Words: Experimental Evolution, Genetics, Osmotic Stress, Saccharomyces cerevisiae