The Bateson-Dobzhansky-Muller (BDM) model of reproductive isolation by genetic incompatibility is a widely accepted model of speciation. Because of the exceptionally rich biological information about the budding yeast Saccharomyces cerevisiae, the identification of BDM incompatibilities in yeast would greatly deepen our understanding of the molecular genetic basis of reproductive isolation and speciation. However, despite repeated efforts, BDM incompatibilities between nuclear genes have never been identified between S. cerevisiae and its sister species S. paradoxus. Such negative results have led to the belief that simple nuclear BDM incompatibilities do not exist between the two yeast species. Here, we explore an alternative explanation that such incompatibilities exist but were undetectable due to limited statistical power. We discover that previously employed statistical methods were not ideal and that a redesigned method improves the statistical power. We determine, under various sample sizes, the probabilities of identifying BDM incompatibilities that cause F1 spore inviability with incomplete penetrance, and confirm that the previously used samples were too small to detect such incompatibilities. Our findings call for an expanded experimental search for yeast BDM incompatibilities, which has become possible with the decreasing cost of genome sequencing. The improved methodology developed here is, in principle, applicable to other organisms and can help detect epistasis in general.
Keywords: genetic incompatibility; odds ratio; reproductive isolation; simulation; speciation; yeast.