Sister chromatid separation occurs in Anaphase of mitosis. At the start of anaphase, cohesins holding sister chromatids together are cleaved by separase, allowing kinetochore microtubules to pull each chromatid (now a daughter chromosome) toward opposite poles. Simultaneously, polar/interpolar microtubules push the poles apart, elongating the cell. Anaphase ensures that each daughter cell receives exactly one copy of each chromosome. This is also called the disjunction of chromosomes.