Which event occurs during prophase of mitosis?

During prophase of mitosis, chromatin undergoes a significant transformation as it condenses into visible chromosomes. This process is essential for ensuring that each daughter cell receives an identical set of chromosomes during cell division. The condensation of chromatin allows the long, thin strands of DNA to coalesce into shorter, thicker structures that can be easily separated. This is crucial because it protects the DNA from damage and organizes it in a way that is manageable for the mitotic apparatus to correctly segregate the genetic material.

The other events mentioned do not occur during prophase. The reassembly of the nuclear envelope takes place during telophase, after the chromosomes have been separated. DNA replication occurs during the S phase of interphase, prior to the commencement of mitosis. Lastly, cytokinesis, the process of cytoplasm division, occurs after mitosis is complete, specifically at the end of telophase, ensuring that the two daughter cells are fully formed. Therefore, the condensation of chromatin into visible chromosomes is a defining feature of prophase, marking the beginning of the mitotic process.