To see prophase animated, click the image.
• Chromosomes become more coiled and can be viewed under a light microscope.
• Each duplicated chromosome is seen as a pair of sister chromatids joined by the duplicated but unseparated centromere.
• The nucleolus disappears during prophase.
• In the cytoplasm, the mitotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell.
• The nuclear envelope disappears at the end of prophase. This signals the beginning of the substage called prometaphase.
To see prometaphase animated, click the image.
• In prometaphase, the spindle enters the nuclear area. Specialized structures called kinetochores have formed on the centromeres of the chromosomes by this time; certain spindle microtubules—the kinetochore microtubules—attach to the kinetochores.