What is prophase characterized by?

Prophase is characterized by significant changes that set the stage for cell division, specifically during mitosis. During this phase, chromatin condenses into distinct chromosomes, making them visible under a microscope. Each chromosome is made up of two sister chromatids joined at a region called the centromere. Additionally, the mitotic spindle starts to form from the microtubules, which will help pull apart the chromosomes during later phases of mitosis.

The formation of the spindle apparatus and the visibility of chromosomes are crucial for the separation of genetic material in the subsequent stages of cell division. The other processes such as chromosomes moving to opposite ends of the cell, spindle fibers disassembling, and nuclear envelope reforming take place in later stages: anaphase, telophase, and during the final steps of the cell cycle, respectively. Thus, the defining features of prophase are the visibility of the chromosomes and the formation of the spindle apparatus.