Final answer:
The Correct option is 3). The event that does not occur during prometaphase is the chromosomes becoming visible with the light microscope. This happens in prophase. During prometaphase, the nuclear envelope completely breaks down, the mitotic spindle is completely formed, and spindle fibers attach to chromosomes.
Step-by-step explanation:
All of the following events occur during prometaphase except the chromosomes become visible with the light microscope. This is because the condensation of the chromosomes, which makes them visible under a microscope, occurs earlier during prophase. During prometaphase, the nuclear envelope completely breaks down and the mitotic spindle is completely formed. The spindle fibers, also known as microtubules, “capture” the chromosomes by attaching to the kinetochores, which are protein structures on the chromosomes.
Furthermore, during prometaphase, the mitotic spindle fibers extend from the centrosomes and some of these microtubules come into contact with and firmly bind to the kinetochores on the sister chromatids. This connection is pivotal for the later alignment of chromosomes on the metaphase plate, and eventual segregation into daughter cells. These processes are a critical part of mitosis, ensuring that each new cell receives an accurate and complete set of chromosomes.