During meiosis, maternal and paternal chromosomes undergo an exchange of DNA, known as crossing over. These crossovers are essential for the proper alignment of homologs on the meiotic spindle and their subsequent segregation into developing gametes. Accordingly, the events of meiosis I are highly coordinated to promote this exchange. Our work has revealed the existence of a novel surveillance system that ensures that each homolog pair has received a crossover. This checkpoint system is activated with the onset of double-strand breaks and feeds back in cis to stabilize the synaptonemal complex, a proteinaceous bridge between homologs.

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