What major event occurs during mitosis prophase?

During prophase, one of the key events is the dissolution of the nuclear membrane, which marks the transition from the interphase to the mitotic phase. As the nuclear envelope disintegrates, the genetic material, which is condensed into visible chromosomes, becomes accessible for the cell's machinery to interact with. Additionally, during this stage, the spindle apparatus begins to form from microtubules, which are crucial for the subsequent attachment to the chromosomes and their movement. This preparation sets the stage for the segregation of chromosomes that will occur in later stages of mitosis.

The other events listed occur at different stages of mitosis. For example, the alignment of chromosomes at the cell equator happens during metaphase, cytoplasm division takes place in cytokinesis after telophase, and the separation of chromatids occurs during anaphase. Thus, the correct understanding of prophase is essential in grasping the overall process of mitosis.