What does not occur during prophase?

During prophase, several critical processes prepare the cell for mitosis. One of the key events that occurs is the condensation of chromatin into visible chromosomes, which allows for easier segregation during cell division. As the chromatin condenses, the DNA becomes tightly packed, forming distinct chromosomes that can be accurately divided between daughter cells.

Another significant process during prophase is the formation of the mitotic spindle, which consists of microtubules and is essential for separating the chromosomes later in mitosis. The spindle fibers emerge from the centrosomes as they move toward opposite poles of the cell, setting the stage for chromosome alignment.

One notable aspect that does not occur during prophase is the reformation of the nuclear envelope. Instead, the nuclear envelope breaks down during prophase, allowing the spindle fibers to interact with the chromosomes. This breakdown is a crucial step, as it provides access for the mitotic spindle to attach to the chromosomes at their kinetochores.

Thus, the correct answer highlights an event that does not happen during prophase, reinforcing the sequence of mitotic events.