During mitosis, what structure directly generates the force that moves sister chromatids toward opposite spindle poles during anaphase?

• A. Shortening (depolymerization) of kinetochore microtubules at the kinetochore and/or spindle pole
• B. Microtubule growth (polymerization) that pushes chromatids away from the poles
• C. Diffusion of chromatids through the nucleoplasm after nuclear envelope breakdown
• D. Extension of actin filaments in the cleavage furrow

Answer: (A)

Verified step by step guidance

1. Understand the key event during anaphase: sister chromatids are pulled toward opposite spindle poles.
2. Recall the role of microtubules in mitosis, especially kinetochore microtubules that attach to chromatids at the kinetochore.
3. Recognize that the force moving chromatids is generated by the shortening (depolymerization) of these kinetochore microtubules, which effectively pulls chromatids toward the poles.
4. Eliminate other options by considering their roles: microtubule polymerization pushes but does not pull chromatids; diffusion is a passive process and not force-generating; actin filaments are involved in cytokinesis, not chromatid movement.
5. Conclude that the direct force comes from the depolymerization of kinetochore microtubules at the kinetochore and/or spindle pole.