Table A1. Frequency of tetrads with at least two detectable recombination events.

MSH5 genotype	SPO11 genotype	No. of NPD (%)	No. of TNCO(%)
Wild type	Wild type	4/462 (0.9)	24/462 (5.2)
	spo11-HA	9/745 (1.2), P = 0.78	44/745 (5.9), P = 0.70
	spo11-yf	16/743 (2.2), P = 0.11	44/743 (5.9), P = 0.70
msh5Δ	Wild type	6/766 (0.8), P = 1.00	31/766 (4.0), P = 0.39

Gfp*⁺ tetrads were enriched by FACS from one culture for wild type, spo11-HA, and spo11-yf and from two independent cultures for msh5Δ (≥302 tetrads analyzed per culture). Statistical significance was evaluated by a Fisher’s exact test (two-tailed P-value) that compared each strain to wild type. Note that the observed NPDs may underrepresent total NPDs because a small fraction of tetrads that appear to display MI nondisjunction (Figure 5G) could have arisen from a four-strand double crossover instead. Such NPD tetrads are expected to be exceedingly rare, however, because they contain a Gfp*⁺ spore that is also Rfp⁺ Cfp⁺, which is an uncommon configuration (≥14-fold less common than the Rfp⁻ Cfp⁻configuration; see Table 2A). All such tetrads were thus scored as “MI nondisjunction.”