Spindle dynamics — During which stage do microtubules grow from spindle poles and attach to kinetochores on each chromatid (capture occurs after nuclear envelope breakdown)?

Introduction / Context:Successful mitosis requires accurate attachment of spindle microtubules to kinetochores. The timing of kinetochore capture is a favorite exam topic because it hinges on nuclear envelope breakdown and dynamic microtubules probing the cytoplasm.

Given Data / Assumptions:

• Spindle poles (centrosomes in animals) nucleate microtubules.
• Nuclear envelope breakdown (NEBD) occurs at prometaphase, enabling kinetochore access.
• Terminology in some curricula groups late prophase and prometaphase closely.

Concept / Approach:Kinetochore capture by dynamic plus ends begins immediately after NEBD, classically termed prometaphase. Many textbooks describe this under late prophase/prometaphase. In contrast, metaphase is the alignment state, anaphase is separation, and telophase is reassembly of nuclei.

Step-by-Step Solution:

Verification / Alternative check:Live imaging shows oscillatory microtubule plus ends sampling kinetochores just after NEBD, consistent with prometaphase timing.

Why Other Options Are Wrong:

• b: Metaphase is post-attachment alignment; not initial capture.
• c: Anaphase follows proper bipolar attachment; capture is complete earlier.
• d/e: Telophase and cytokinesis occur after chromosome segregation.

Common Pitfalls:Equating metaphase alignment with first attachment; overlooking the specific role of NEBD in enabling kinetochore access.

Final Answer:Prophase (including prometaphase transition)