Question

which of these has occurred by the end of prophase?
the nuclear membrane has disappeared.
sister chromatids have separated.
the chromosomes are lined up in the middle.
the cell membrane has begun to pinch inward.

Explanation:

• During prophase of mitosis, the nuclear membrane breaks down (disappears).
• Sister chromatids separate during anaphase.
• Chromosomes lining up in the middle occurs during metaphase.
• Cell membrane beginning to pinch inward happens during cytokinesis (after telophase).

Answer:

The nuclear membrane has disappeared.