Spindle fiber detachment occurs at the end of anaphase/telophase

Steps:

• Recall mitosis stages: spindle fibers form and attach to centromeres in prometaphase, align in metaphase, shorten in anaphase to separate chromosomes.
• Note that centromeres detach from spindle fibers during telophase as the spindle disassembles.
• Examine graph regions: identify where mean spindle length decreases to zero, indicating full detachment.
• Match this to the final region, as prior regions show attachment and shortening but not complete release.

Why D is correct:

• Region D corresponds to telophase, when spindle fibers fully depolymerize and detach from all centromeres, per mitotic spindle dynamics.

Why the others are wrong:

• A: Shows prophase/prometaphase fiber formation with attachment, not detachment.
• B: Represents metaphase alignment with stable, attached fibers.
• C: Indicates anaphase shortening while centromeres remain attached during chromosome separation.

Final answer: D