Deamination of cytosine resulting in the dU:dG mismatch is one of the most common single-base-altering lesions in non-replicating DNA. "Spo11" mutants of the fission yeast "Schizosaccharomyces pombe" and "C. elegans" undergo meiotic crossover recombination and proper chromosome segregation when dU:dG lesions are produced in their DNA. This crossover recombination does not involve the formation of large numbers of double-strand breaks, but does require uracil DNA-glycosylase, an enzyme that removes uracil from the DNA phosphodiester backbone and initiates base excision repair. Thus, it was proposed that base excision repair of DNA damage such as a uracil base, an abasic site, or a single-strand nick is sufficient to initiate meiotic crossover recombination in "S. pombe" and "C. elegans".