S. cerevisiae strains analyzed in this study.

MLH1 and PMS1 from the above strains were sequenced in-house (S) or were obtained from publicly available data bases (R; http://www.yeastgenome.org/; http://www.sanger.ac.uk/Teams/Team71/durbin/sgrp/; http://www.broad.mit.edu/annotation/fungi/comp_yeasts/). * For more details see: http://wiki.yeastgenome.org/index.php/CommunityW303.html. In the class column strains were grouped (see Figure 2) with respect to MLH1 761 (G or D) and PMS1 818 (R or K). The S288c-like genotype (MLH1-D, PMS1-R) is indicated as C, the SK1-like genotype (MLH1-G, PMS1-K) as K, and the predicted ancestral genotype (MLH1-G, PMS1-R) as A.