What event occurs during prophase?

During prophase, the chromosomes become visible under a light microscope as they condense and shorten, making them easier to see. This is the stage when the chromatin, which is loosely packed DNA, undergoes significant structural changes to form distinct, tightly coiled chromosomes. The nuclear envelope that encases the nucleus typically begins to break down and disappears during this phase, allowing the spindle fibers to attach to the chromosomes.

This understanding of prophase is essential in the context of the entire cell division process, specifically mitosis. The visibility of chromosomes is a key indicator that the cell is preparing to divide, and the dissolution of the nuclear envelope is critical for the later stages of mitosis to properly occur. Other options refer to events that take place in different stages of the cell cycle, highlighting the specific timing and occurrence of cellular actions during mitosis.