In vivo, the antiCO effect of BLM/Sgs1 helicase was demonstrated by the fact that yeast sgs1 mutants as well as Bloom's syndrome patients or BLM-deficient mice have elevated rates of mitotic recombination (either reciprocal sister chromatid exchanges (SCE) or increased frequency of exchange between homologous chromosomes) [11]–[14]. Here, BLM is linked to Bloom syndrome.