Loss or gain of chromosomes is associated with many cancer cells. This property, called chromosome instability, might arise from a lesion in the chromosome segregation machinery. In mitosis, chromatin is structurally reorganized into chromosomes in which replicated DNA molecules are seen as sister chromatids. Each chromosome is then captured by two opposing poles of the spindle which allows the segregation of sister chromatids towards opposite poles. Our ultimate goal is to understand how chromosomes condense, achieve bipolar spindle attachments and how cohesion is subsequently dissolved to allow sister chromatid separation. Elucidating these processes should provide insight into the mechanisms underlying chromosome instability in cancer cells.