During Anaphase, which event occurs?

• A. Centromeres split, chromosomes are pulled toward the two centrioles
• B. Nucleoli disappear
• C. Nuclear envelope appears
• D. Chromatids attach to the spindle fibers

Answer: (A)

In anaphase the sister chromatids separate at the centromeres and are pulled toward opposite poles of the cell. This happens because the kinetochore microtubules shorten, tugging each chromatid toward the pole it’s attached to, so the chromosomes move to opposite ends. At the same time, nonkinetochore microtubules lengthen and push the poles farther apart, helping the cell elongate in preparation for division. This stage is distinct from other events: nucleoli disappear earlier in prophase as chromatin condenses; the nuclear envelope re-forms later in telophase; and chromatids first attach to spindle fibers during prometaphase.