Describe the key events of prophase and metaphase.
During prophase, the key events include chromosome condensation, centriole migration, spindle formation, and the breakdown and disappearance of the nuclear membrane and of the nucleoli. By late prophase, each individual chromosome's twin chromatids become visible, appearing as short rod like structures. Kinetochore microtubules, which will eventually attach the chromosomes to the spindle, begin to radiate from each chromosome's centromere. The disintegration of the nuclear membrane allows the spindle's fibers to enter the nucleus. During metaphase, the kinetochore fibers radiating from each centromere become linked to two polar microtubules, one from each pole of the cell. As a consequence of this interconnection, the chromosomes become aligned near the equatorial plane of the cell.
