What occurs during prophase in mitosis?

During prophase in mitosis, a key event is the coiling and condensing of chromatin into visibly distinct chromosomes. This process is essential because it allows for the chromosomes to be accurately segregated during later stages of mitosis. When chromatin becomes tightly coiled, each chromosome is composed of two sister chromatids joined at the centromere, making them easier to maneuver within the cell.

The visibility of chromosomes at this stage is crucial for proper alignment and segregation, which occurs in the subsequent phase, metaphase. The changes that take place during prophase also prepare the cell for the division process. While the nucleolus may start to disassemble, it does not completely break down at this stage, and the formation of the spindle apparatus begins, but it is the condensation of chromatin that defines prophase. This organized structure ensures that the genetic material is protected and easily divisible as the cell progresses to the next phases of mitosis.