Spindle fiber detachment occurs at the end of anaphase/telophase

Steps:

• Recall mitosis stages: spindle fibers form and attach to centromeres in prometaphase, align chromosomes in metaphase, shorten during anaphase to separate sister chromatids, and detach/disassemble in telophase.
• Analyze graph trends: fiber length increases initially (formation), plateaus (metaphase alignment), decreases gradually (anaphase shortening), then drops sharply (telophase detachment).
• Identify detachment point: centromeres detach when fibers fully shorten and disassemble, after all chromosomes reach poles.
• Match to regions: the final decreasing region indicates complete detachment.

Why D is correct:

• Region D shows the sharp decline in length, corresponding to telophase disassembly when all centromeres detach per mitotic spindle dynamics.

Why the others are wrong:

• A: Early increase reflects fiber formation and attachment, not detachment.
• B: Plateau indicates metaphase stability with centromeres still attached.
• C: Gradual decrease is anaphase shortening with centromeres partially engaged.

Final answer: D