Core mitosis milestone — Which phase of mitosis is specifically associated with the separation of sister chromatids into individual chromosomes?

Introduction / Context:
Identifying cell-cycle phases is foundational in cell biology and histology. The defining event asked here is sister chromatid separation, which changes one replicated chromosome (two chromatids) into two independent chromosomes moving toward opposite poles.

Given Data / Assumptions:

• Sister chromatids are held together by cohesin until anaphase onset.
• The mitotic spindle is established before separation occurs.
• Phase names: prophase, prometaphase, metaphase, anaphase, telophase.

Concept / Approach:
At metaphase, chromatids are aligned at the equator. Anaphase begins when separase cleaves cohesin, kinetochore microtubules depolymerize, and chromatids move to opposite poles (anaphase A), while the spindle elongates (anaphase B). Telophase re-forms nuclei around the separated chromosome sets.

Step-by-Step Solution:

Verification / Alternative check:
Microscopy images of mitotic cells show clear chromatid-to-pole movement beginning at anaphase onset, not earlier.

Why Other Options Are Wrong:

• a: Prophase condenses chromosomes; separation has not started.
• b: Metaphase is alignment, not separation.
• d: Telophase follows separation and involves nuclear reassembly.
• e: Prometaphase is kinetochore capture after nuclear envelope breakdown.

Common Pitfalls:
Confusing metaphase alignment with anaphase segregation; overlooking the requirement of cohesin cleavage by separase.

Final Answer:
Anaphase