All organisms with aerobic metabolism are subjected to oxygen and its reactive species (ROS) that cause oxidative stress to the organism. Oxidative stress happens when all cellular antioxidative mechanisms are overwhelmed and cannot keep up with removing ROS from the cell or fix the damage ROS caused to the cell. Resistance to oxidative stress is a polygenic trait in the yeast Saccharomyces cerevisiae. Improved oxidative stress resistance is highly desirable in industry, where the use of robust strains, which can uphold different stressful conditions, is more cost-effective. We intended iterative crossing of 3 yeast strains. We arranged them from the least to the most resistant and crossed the least resistant strain with the SGA strain Y7092. After crossing we chose the most resistant segregant. We planned to repeat the process two more times to shift the expressed phenotype to a more extreme level. The chosen segregant after the first iteration was more resistant to oxidative stress, caused with copper (II) sulphate, than both parental strains. When exposed to stress, caused with hydrogen peroxide, the segregant was more resistant than one of the parental strains. Therefore, we have in just one iteration succeeded to move the level of resistance to oxidative stress to a higher degree compared to the parental strains used.
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