Mitosis stage based on chromosome-spindle alignment and movement

Steps:

• Recall mitosis stages: metaphase involves chromosomes lining up at the equator with spindle fibers attached to kinetochores.
• Note that attached spindle fibers indicate bipolar attachment, characteristic of metaphase.
• Observe if the diagram shows tension or initial movement, which aligns with late metaphase transitioning to separation.
• Match to choice D, as it describes attachment and pulling action during alignment.

Why D is correct:

• By definition, in metaphase, spindle fibers attach to sister chromatids and exert opposing forces, pulling them toward poles while maintaining equatorial position until cohesion breaks.

Why the others are wrong:

• A: In anaphase, chromosomes move away from the equator toward poles, not toward centromeres, which are central structures.
• B: Describes positioning prior to separation but omits spindle attachment and tension implied in the diagram.
• C: Anaphase involves movement away from the equator, not pulling while still along it.

Final answer: D