A Genetic Comparison of Baker’s and Brewer’s Yeast

Kramer, Trenton

A Genetic Comparison of Baker’s and Brewer’s Yeast

Persistent URL

https://dspace.allegheny.edu/handle/10456/56760

Author(s)

Kramer, Trenton

Date Issued

April 3, 2023

Abstract

Brewer's yeast and baker's yeast are two strains of Saccharomyces cerevisiae with a long history of domestication by humans to perform best in the production of beer and bread, respectively. Despite being the same species, brewer's yeast and baker's yeast have significant differences in gene expression for at least 20 genes (Davydenko et al., 2020). However, it is not known whether the amino acid sequence of these 20 genes differs between brewer’s and baker’s yeast, and whether there is any evidence that positive natural selection acting on the different strains may have been responsible for any differences in amino acid sequence. To answer this question I performed a dN/dS comparison of the 20 genes for baker’s, brewer’s, and wild yeast. dN/dS is the ratio of the rate of nonsynonymous changes over the rate of synonymous changes in the DNA sequence. A dN/dS ratio greater than 1 provides strong evidence that the difference in the DNA sequence was caused by positive Darwinian selection acting on variation in the amino acid sequence of the resulting protein. A ratio less than 1 is more consistent with the hypothesis that changes in amino acid sequence were likely caused by genetic drift acting on selectively neutral mutations rather than natural selection. Overall, I found no evidence of positive selection acting on any of the 20 genes, as dN/dS ratios were all <1 and generally low. However, comparisons for 3 genes —IPP1, YCP4, and ZRT1 — produced intriguing results suggesting a possible role for positive selection and should be investigated further.

Major

Biology

First Reader(s)

Mumme, Ronald L.