In Saccharomyces cerevisiae, meiotic recombination is initiated by Spo11-dependent double-strand breaks (DSBs), a process that precedes homologous synapsis. Here we use an antibody specific for a phosphorylated histone (-H2AX, which marks the sites of DSBs) to investigate the timing, distribution and Spo11-dependence of meiotic DSBs in the mouse. We show that, as in yeast, recombination in the mouse is initiated by Spo11-dependent DSBs that form during leptotene. Loss of -H2AX staining (which in irradiated somatic cells is temporally linked with DSB repair) is temporally and spatially correlated with synapsis, even when this synapsis is 'non-homologous'.
Mahadevaiah, S. K., Turner, J. M. A., Baudat, F., Rogakou, E. P., & de Boer, P. (2001). Recombination DNA double strand breaks in mice precede synapsis. Nature Genetics, 27, 271-276. https://doi.org/10.1038/85830