Table 2.

Random spore analysis of recombination at the ARG4 locus.

	Number of spore clones (% of total)
	Parental		Nonparental
Genotype	Ura+ Thr+	Ura− Thr−	Ura− Thr+	Ura+ Thr−	Total	% Nonparental	Significance
Wild type	134 (4.2)	1322 (41.1)	1525 (47.4)	239 (7.4)	3220	54.8
HA/HA	159 (4.8)	1186 (36.0)	1754 (53.3)	194 (5.9)	3293	59.2	p = 0.0004
yf-HA/HA	149 (4.1)	1120 (30.6)	2207 (60.4)	180 (4.9)	3656	65.3	p = 1 × 10−7
da-HA/da-HA	130 (5.5)	633 (26.8)	1534 (64.8)	69 (2.9)	2366	67.8	p = 3 × 10−7

Random spores from strains carrying the recombination reporter diagrammed in Figure 2 and the indicated SPO11 genotypes were plated on medium lacking arginine to select for Arg+ recombinants, then the configuration of flanking markers was scored. Data were pooled from three independent cultures of each strain (≥661 spore clones per culture). Statistical significance was evaluated by G test for the distribution of spore types for each strain compared to the strain listed above it. The majority (∼90%) of the recombinants with a parental configuration of flanking markers were Ura− and Thr−. This is the expected pattern because of the polarity of gene conversion at this locus (Nicolas et al., 1989). Specifically, in recombination initiated by a DSB, the broken chromosome is the recipient of genetic information. The arg4-Nsp mutation is closer to the DSB site (Figure 2B), so conversion of this mutation to wild type accounts for most of the noncrossover Arg+ recombinants. Thus, Arg+ progeny arising from a noncrossover event will inherit the parental configuration from the original arg4-Nsp chromosome. The same feature of the locus accounts for the fact that the majority (∼90%) of the Arg+ spores with a nonparental configuration were Ura− Thr+.