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. Author manuscript; available in PMC: 2007 Aug 15.
Published in final edited form as: Cell. 2006 Jul 28;126(2):285–295. doi: 10.1016/j.cell.2006.05.044

Figure 2.

Figure 2

Crossover homeostasis occurs at the expense of noncrossovers.

(A, B) Maps of the assay region showing configuration of the arg4 alleles and flanking markers.

(C) Random spore analysis of recombination at ARG4. Random spores from strains heterozygous for arg4-Nsp and arg4-Bgl were plated on SC-arginine to select for Arg+ recombinants. Spore clone colonies were patched onto SC-arginine plates, then replica-printed onto SC-uracil and SC-threonine to score flanking markers. Examples of parental and nonparental clones are indicated.

(D) Reduced Spo11 activity is accompanied by an increased crossover/noncrossover ratio. The ratio of crossovers to noncrossovers for Arg+ recombinants was calculated from the random spore data after correcting for incidental crossovers (see text). Gray lines show expected patterns for no homeostasis and for complete homeostasis. The curve for complete homeostasis was calculated assuming that 70% of crossovers in wild type were interference sensitive, with the remainder not subject to crossover homeostasis. Similar curves are obtained for interfering crossover values of 60-85% (data not shown).