Human cells store their genetic information into 46 chromosomes. To maintain vital genetic information, a whole set of chromosomes must be inherited precisely by daughter cells when cells divide. Errors in this process would cause cell death and various human diseases, such as spontaneous miscarriage during pregnancy, genetic abnormalities and cancers. For instance, about one third of spontaneous miscarriage and the majority of genetic abnormalities (monosomy and trisomy; e.g. Down syndrome) are thought to stem from errors in chromosome inheritance during the process that generates sperms and eggs. Cancer is also a major threat to human health as it kills about one in four adults (in developed countries). Although cancer development is a complex process, it is now widely accepted that errors in chromosome inheritance, causing abnormal number of chromosomes in cells, is one of the initial events leading to generation of cancers. Thus, errors in chromosome inheritance to daughter cells causatively account for a considerable portion of all these diseases. Our research aims to reveal fundamental mechanisms ensuring chromosome inheritance when cells divide. Therefore, outcomes from our research should contribute to understanding the mechanisms of the human diseases that critically endanger human health all over the world.