Inheritance in tetraploid yeast revisited: segregation patterns and statistical power under different inheritance models.

In their recent article, Albertin et al. (2009) suggest an autotetraploid origin of 10 tetraploid strains of baker's yeast (Saccharomyces cerevisiae), supported by the frequent observation of double reduction meiospores. However, the presented inheritance results were puzzling and seemed to contradict the authors' interpretation that segregation ratios support a tetrasomic model of inheritance. Here, we provide an overview of the expected segregation ratios at the tetrad and meiospore level given scenarios of strict disomic and tetrasomic inheritance, for cases with and without recombination between locus and centromere. We also use a power analysis to derive adequate sample sizes to distinguish alternative models. Closer inspection of the Albertin et al. data reveals that strict disomy can be rejected in most cases. However, disomic inheritance with strong but imperfect preferential pairing could not be excluded with the sample sizes used. The possibility of tetrad analysis in tetraploid yeast offers a valuable opportunity to improve our understanding of meiosis and inheritance of tetraploids.