DNA endonuclease, which specifically mediates DNA cleavage that forms the double-strand breaks (DSB) that initiate meiotic recombination. SPO11 covalently attaches itself to the 5' DNA strand during DSB formation and each strand is cleaved by a composite active site assembled at the interface of two SPO11 monomers, with the two cleavages staggered to produce a two-nucleotide 5' overhang. SPO11 cleavage site selection is driven by a mild sequence bias and a preference for bendable and underwound DNA. Together with TOP6BL, promotes relaxation of negative and positive supercoiled DNA and DNA decatenation through cleavage and ligation cycles. Required for the phosphorylation of SMC3, HORMAD1 and HORMAD2. . This is the function of ENSG00000054796 (SPO11, SPO11 initiator of meiotic double strand breaks).