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Mitosis
Concept 5: Prophase
Concept 8: Telophase
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Concept 9: Mitosis Animated
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Concept 5: Prophase
Chromosomes become visible, the nucleolus disappears, the mitotic spindle forms, and the nuclear envelope disappears.
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.