During which phase do chromosomes condense and the nuclear envelope breaks down?

During the prophase of cell division, chromosomes undergo a significant transformation as they condense into distinct, visible structures. This is a critical step because it allows the chromosomes to become compact and organized, making them easier to separate later in the process. Additionally, during prophase, the nuclear envelope, which encloses the nucleus, begins to disintegrate. This breakdown is crucial as it facilitates the interaction of the chromosomes with the mitotic spindle, a structure essential for chromosome movement.

The condensation of chromosomes and the breakdown of the nuclear envelope are key events in preparing the cell for the subsequent stages of mitosis, particularly metaphase, where the chromosomes align at the cell's equator. Understanding the significance of these changes during prophase highlights how cells efficiently prepare for division and ensure accurate distribution of genetic material.