By developing a statistical model to account for the genetic interactions, they could genotype any combination of the four SNPs in either strain of yeast and predict with a high level of confidence their effect on sporulation.
But in that study, the yeast were grown in the same environment glucose.
In the current study, the scientists grew the two yeast strains with all 16 combinations of four SNPs in different simple sugars: glucose, fructose, sucrose, maltose, raffinose, grape juice, galactose and a combination of sucrose, glucose and fructose.
"These were all mono- or di-saccharides, so the environments are not radically different from one another," Cohen explains. "It's not like we heated up the yeast or froze them, added acids or put them in a centrifuge. We simply changed the carbon source and measured the effects of those four SNPs in the different environments."
Surprisingly, the researchers found that the effects of the four SNPs on spore production were dramatically different in the different environments. The effects of different combinations of SNPs in one environment were not an accurate predictor of the effects of those same SNPs in other environments.
For example, one combination of the four SNPs increased sporulation efficiency by 40 percent in glucose, but that same SNP combination increased efficiency by 80 percent when the yeast were grown in raffinose.
Indeed, the relative importance of particular SNPs and their interactions were not constant but varied with the genetic background of the yeast strain and the environment.
"Having a particular combination of SNPs was never a great predictor," Cohen says. "If we didn't know the environment in which the yeast were grown, we could not accurately predict the effect of the S
|Contact: Caroline Arbanas|
Washington University School of Medicine