Figure 3.

Mutations in the mutator pathway can restore crossover formation in the spo-11 mutant. (A) Representative wild-type and mutant diakinesis oocytes stained with HTP-3 (white) and DAPI (red) to allow for counting of the number of the number of bivalents (homologous chromosomes connected by chiasmata) or univalents in each strain. Yellow arrows in mut-7; spo-11 and mut-16; spo-11 point to a single pair of non-recombinant chromosomes. Scale bars, 5μm. (B) Graph indicating the number of DAPI-stained bodies in diakinesis oocytes for each genotype. Wild-type oocytes display six DAPI-stained bivalents, representing the six pairs of chromosomes held together by chiasmata, while spo-11, which fails to make double-strand breaks for recombination, displays 12 DAPI-stained univalents. Mutations in the mutator pathway but not the piRNA pathway can partially rescue the spo-11 phenotype. Occasionally, two bivalents lie too close together to be visually resolved, resulting in a modest underestimation of the number of DAPI-stained bodies. (C) Mean number of DAPI-stained bodies scored for each of the genotypes in (B). Total number of oocytes scored is indicated in parentheses.