Phases of Mitosis Practice Test

Cohesin’s job is to keep sister chromatids joined after DNA replication, so they stay attached and can be pulled apart accurately during segregation. This protein complex forms a ring that encircles the paired chromatids, especially at the centromeres, providing the cohesion needed for proper alignment at metaphase. At the transition to anaphase, the cell activates separase, which cleaves a subunit of cohesin, releasing the sister chromatids so motor proteins and shortening spindle microtubules can pull them to opposite poles. This removal occurs at the onset of anaphase.

Cohesin does not condense chromosomes (that’s condensin), it does not form spindle fibers (those are microtubules built from tubulin), and it does not trigger cytokinesis (driven by the actomyosin contractile ring and related signals).