Which phase of mitosis involves the chromosomes condensing and the nuclear envelope breaking down?

• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Telophase

Answer: (A)

Chromosome condensation and the breakdown of the nuclear envelope occur at the start of mitosis, in prophase. As the cell prepares to divide, chromatin condenses into visible chromosomes, making them easier to segregate. At the same time, the nuclear envelope breaks down so the spindle fibers can attach to the chromosomes and move them. By metaphase the chromosomes are already condensed and the envelope is gone, so the key events of condensation and envelope breakdown happen in prophase. In later phases, chromosomes align at the center (metaphase), are pulled apart (anaphase), and the envelope re-forms around the separated chromosomes (telophase).