The gene encoding Spo11 shares sequence similarity to TopoVI, a type II topoisomerase. A Spo11 dimer cleaves both strands of DNA. Each subunit of the dimer remains covalently attached to the 5' end of one strand of DNA via a phosphodiester linkage to a conserved tyrosine residue of Spo11 (Romanienko and Camerini-Otero 2000, Baudat et al. 2000, Mahadevaiah et al. 2001, Zenvirth et al. 2003). In addition to Spo11, work from budding yeast has shown a total of 7 proteins essential for double strand break formation. The mammalian ortholog of Mei4 (S. cerevisiae) as well as a mammalian specific gene called Mei1 are essential to formation of meiotic double strand breaks (Kumar et al.2010, Libby et al. 2003).