Mitosis: Prophase

Prophase is the beginning of mitosis. During interphase, the chromosomes are loosely dispersed in the nucleus.  Remember that chromosomes are replicated during the S phase of Interphase and replication of the chromosomes is possible because they are dispersed.  It is difficult to pick out an individual chromosome because they are each so spread out. In prophase, the chromosomes in the nucleus change from being loosely dispersed to becoming more condensed. This change in chromosome structure makes them easier to move around the cell, an important structural change for what is about to happen. As the chromosomes condense they get shorter and thicker and can be seen through the microscope as individual structures (Fig. 3). The chromosomes at prophase will consist of two identical parts called sister chromatids that stay connected at the centromere. It is now clear that the chromosomes have been replicated. Next, the nucleus is dissolved. At the end of prophase the replicated chromosomes are moved by the spindle apparatus to the center of the cell.

Figure 3. Prophase of mitosis. (Image by Marjorie Hanneman)

Figure 4.  Cells in several stages of mitosis division. (Image from Doc. RNDr. Josef Reischig, CSc., CC BY-SA 3.0, via Wikimedia Commons .)