Abstract: In proliferating cells, sister chromatid cohesion is established depending on Rad21 cohesin complexes during S phase and maintained until metaphase, and required for equational chromosome segregation in mitosis. In meiosis, however, the cohesin complexes are largely replaced by meiosis-specific cohesin complexes including Rec8, thereby establishing reductional chromosome segregation to produce haploid gametes (Watanabe & Nurse, Nature 1999). In addition to Rec8, our lab has identified and characterized shugoshin (Sgo1) and meikin (Moa1) in fission yeast, which critically regulate the functions of Rec8. Importantly, these key meiotic factors and their functions turned out to be conserved in human. I will discuss how Rec8, Sgo1 and Moa1 interplay to establish meiotic chromosome segregation, and how disorder of the system influence egg aneuploidy, which is a major cause of miscarriage and congenital diseases such as Down syndrome in human.