Isolates containing heterozygous MLH1-PMS1 genotypes predicted to form mutator spore progeny. Eighteen isolates were identified from the 1011 yeast genome project that are heterozygous for the MLH1 761 and/or PMS1 818/822 genotypes, and are predicted to yield incompatible spore progeny (Bui et al. 2017). In Figure S1, a model is presented in which ancestral isolates bearing MLH1 Gly 761 and PMS1 Arg 818/822 alleles acquire neutral or beneficial mutations that lead to the derived S288c (purple, Asp 761, Arg 818/822) and SK1 (green, Gly 761, Lys 818/822) group isolates.