Cell division fundamentals — phase associated with nuclear envelope re-formation During mitosis, at which stage does the nuclear envelope reappear around separated sets of chromosomes?

Introduction / Context:
Mitosis is a precisely ordered process that ensures equal distribution of duplicated chromosomes into two daughter nuclei. A common exam concept is identifying at which stage specific structural events occur, such as chromosome condensation, spindle attachment, chromatid separation, and nuclear envelope dynamics. This question targets recognition of the stage when the nuclear envelope reforms.

Given Data / Assumptions:

• Eukaryotic cell undergoing mitosis (not meiosis).
• Standard sequence of phases: prophase, prometaphase, metaphase, anaphase, telophase, followed by cytokinesis.
• Nuclear envelope breaks down early and reassembles later in the cycle.

Concept / Approach:
The nuclear envelope disassembles during prometaphase to permit spindle microtubules to attach kinetochores on condensed chromosomes. After sister chromatids separate in anaphase and migrate to opposite poles, the cell must re-establish two nuclei. Reassembly of the nuclear envelope around each set of chromosomes is a hallmark of telophase, accompanied by chromosome decondensation and restoration of nucleoli.

Step-by-Step Solution:

Verification / Alternative check:
Microscopy textbooks and atlases consistently illustrate vesicle-mediated reassembly of nuclear membranes around the chromatid masses during telophase, often concurrent with initiation of cytokinesis (cleavage furrow or cell plate).

Why Other Options Are Wrong:

• Prophase: chromosomes condense; envelope still intact until prometaphase.
• Metaphase: chromosomes align at the equator; envelope is absent.
• Anaphase: chromatids separate and move; envelope has not yet re-formed.
• Cytokinesis: cytoplasmic division; nuclear envelope re-formation is already underway from telophase.

Common Pitfalls:
Confusing late anaphase with telophase; remember that envelope reassembly and chromatin decondensation signify entry into telophase.

Final Answer:
Telophase