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Copyright 2004 by the Genetics Society of America DOI: 10.1534/genetics.104.033266

Summary: Copyright 2004 by the Genetics Society of America
DOI: 10.1534/genetics.104.033266
Haploidy, Diploidy and Evolution of Antifungal Drug Resistance
in Saccharomyces cerevisiae
James B. Anderson,1
Caroline Sirjusingh and Nicole Ricker
Department of Botany, University of Toronto, Mississauga, Ontario L5L 1C6, Canada
Manuscript received July 2, 2004
Accepted for publication September 15, 2004
We tested the hypothesis that the time course of the evolution of antifungal drug resistance depends
on the ploidy of the fungus. The experiments were designed to measure the initial response to the selection
imposed by the antifungal drug fluconazole up to and including the fixation of the first resistance mutation
in populations of Saccharomyces cerevisiae. Under conditions of low drug concentration, mutations in the genes
PDR1 and PDR3, which regulate the ABC transporters implicated in resistance to fluconazole, are favored.
In this environment, diploid populations of defined size consistently became fixed for a resistance mutation
sooner than haploid populations. Experiments manipulating population sizes showed that this advantage
of diploids was due to increased mutation availability relative to that of haploids; in effect, diploids have
twice the number of mutational targets as haploids and hence have a reduced waiting time for mutations
to occur. Under conditions of high drug concentration, recessive mutations in ERG3, which result in


Source: Anderson, James B. - Department of Ecology and Evolutionary Biology, University of Toronto


Collections: Environmental Sciences and Ecology