Originally published as Genetics Published Articles Ahead of Print on July 29, 2007.

Genetics, Vol. 177, 449-456, September 2007, Copyright © 2007
doi:10.1534/genetics.107.077859

Complex Genetic Changes in Strains of Saccharomyces cerevisiae Derived by Selection in the Laboratory

Joshua T. Witten, Christina T. L. Chen and Barak A. Cohen1

Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63108

1 Corresponding author: Box 8510, 4444 Forest Park Pkwy., St. Louis, MO 63108.
E-mail: cohen{at}genetics.wustl.edu

Selection of model organisms in the laboratory has the potential to generate useful substrates for testing evolutionary theories. These studies generally employ relatively long-term selections with weak selective pressures to allow the accumulation of multiple adaptations. In contrast to this approach, we analyzed two strains of Saccharomyces cerevisiae that were selected for resistance to multiple stress challenges by a rapid selection scheme to test whether the variation between rapidly selected strains might also be useful in evolutionary studies. We found that resistance to oxidative stress is a multigene trait in these strains. Both derived strains possess the same major-effect adaptations to oxidative stress, but have distinct modifiers of the phenotype. Similarly, both derived strains have altered their global transcriptional responses to oxidative stress in similar ways, but do have at least some distinct differences in transcriptional regulation. We conclude that short-term laboratory selections can generate complex genetic variation that may be a useful substrate for testing evolutionary theories.