Which event occurs during Late Prophase?

• A. The chromosomes line up in the middle of the cell
• B. The nuclear envelope fragments and the spindle forms
• C. Chromosomes become visible and spindles form
• D. The nuclear envelope breaks up, allowing the spindle to interact with the chromosomes

Answer: (D)

During late prophase, the nucleus has largely disassembled and the spindle apparatus is ready to interact with the chromosomes. The nuclear envelope breaks apart, removing the barrier that kept chromosomes separated from the spindle, so microtubules can attach to kinetochores and抓 hold of the condensed chromosomes. This sets up their movement toward the center of the cell in preparation for metaphase. Earlier in prophase, chromosomes condense and become visible and the spindle begins to form, while metaphase is when chromosomes line up at the cell's equator. So the breaking up of the nuclear envelope to allow spindle contact with the chromosomes is the defining event of this stage.