Cell division stages: Which mitotic stage begins when sister chromatids align at the cell’s equatorial plane (the metaphase plate)?

Introduction / Context:
Mitosis is classically divided into prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis. Recognizing key hallmarks (chromosome condensation, spindle attachment, alignment, separation) is essential for microscopy and cell cycle analysis.

Given Data / Assumptions:

• Sister chromatids have formed during S phase and are held together by cohesin.
• Spindle microtubules attach to kinetochores during prometaphase.
• We focus on the moment of alignment across the equatorial plane.

Concept / Approach:
Metaphase is defined by all chromosomes aligning at the metaphase plate with bipolar attachment to spindle poles. Anaphase begins only after cohesin cleavage allows chromatids to move toward opposite poles. Prophase precedes spindle attachment, and telophase follows chromatid separation.

Step-by-Step Solution:

Verification / Alternative check:
Microscopy of synchronized cells shows maximal chromosome condensation and equatorial alignment at metaphase, often used as a checkpoint to ensure correct attachment.

Why Other Options Are Wrong:

• Anaphase: begins after separation, not at alignment.
• Prophase: chromosomes condense; alignment has not occurred.
• Interphase: not part of mitosis.
• Telophase: follows anaphase; chromosomes decondense and nuclei reform.

Common Pitfalls:
Confusing prometaphase (attachment) with metaphase (complete alignment), and mixing mitosis with cytokinesis.

Final Answer:
Metaphase