Mitosis Progression: From Metaphase to Anaphase

Steps:

• Assume photomicrograph shows metaphase: sister chromatids aligned and attached at centromeres, nuclear membrane absent.
• In next stage (anaphase), spindle fibers pull sister chromatids apart to opposite poles.
• Chromatids separate, so no longer attached as pairs.
• Nuclear membrane stays absent during anaphase, re-forming later in telophase.

Why A is correct:

• Anaphase features separated sister chromatids (not attached) with nuclear membrane still absent, per mitosis stage definitions.

Why the others are wrong:

• B: Nuclear membrane re-forms in telophase, not anaphase.
• C: Sister chromatids remain attached until anaphase begins.
• D: Nuclear membrane breakdown occurs in prophase, not the next stage.

Final answer: A