When cells divide, chromosomes need to be evenly segregated between daughter cells. This equal distribution of chromosomes is very important to accurately pass on genetic information to the next generation. Abnormal chromosomal segregation, on the other hand, can cause cell death (apoptosis) or diseases like Down syndrome and cancer. In order for chromosomes to equally divide, it is necessary first to bind the filamentous spindle fiber to a specific region, the centromere, of the chromosome. For the spindle fiber to be correctly joined, it is essential that a part of the chromosome has a special structure called heterochromatin. However, the mechanism for forming this structure has not been sufficiently clarified.