Prophase
At the beginning of prophase, the chromatin network becomes visible as it condenses into separate chromosomes. As this stage moves on the chromosomes become more distinct, as well as shorter and thicker because of the condensing of their coils. The chromosomes consist of two identical sister chromatids joined by a centromere. By the end of prophase, the nuclear envelope and nucleolus have disappeared completely. Spindle fibers then form and span the cell, expanding the middle. Centrioles control the formation of these spindle fibers. There is a set at each pole. The next step in the cell cycle, the second stage of mitosis, is metaphase.
Learn about metaphase
