Which event characterizes anaphase of mitosis?

• A. Sister chromatids are pulled apart to opposite sides
• B. The nucleus re-forms around chromosomes
• C. Chromosomes align at the center
• D. Spindle fibers disassemble

Answer: (A)

During mitotic anaphase, the sister chromatids are pulled apart and moved to opposite poles of the cell. This separation happens after the cohesin proteins holding the chromatids together are cleaved, allowing each chromatid to be pulled away by shortening kinetochore microtubules. At the same time, forces from microtubules lengthening between poles push the poles further apart, broadening the cell.

This event is distinct from other stages: metaphase features chromosomes aligned at the cell’s equator; telophase involves the reformation of the nuclear envelope around the separated chromatids; and spindle fibers begin to disassemble as the cell completes division.