The Phases of Mitosis

Now, let's look at what happens during each stage of Mitosis:


PROPHASE:  In this phase, long, stringy chromosomes begin to become visible as they coil up.  Each duplicated chromosome is seen as a pair of sister chromatids joined by a centromere.  Sister chromatids and the DNA they contain are exact copies of each other.  The nucleolus disappears.
In the cytoplasm, the mitotic spindle, consisting of microtubules, forms between the two pairs of centrioles as they migrate to opposite ends, or poles, of the cell.
The nuclear envelope begins to disappear and is gone by the end of prophase.
The mitotic spindle, a football-shaped structure of thin microtubules begins to form between the divided centrioles.  The spindle fibers play an important role in the separation of sister chromatids in a later stage of mitosis.
Now, for a drawing of a cell in mid/late Prophase, please go to:
www.riaxin.com/images/cells/cd2t.gif


METAPHASE:  During Metphase, sister chromatids attach to the spindle fibers by their centromeres.  The chromosomes are pulled to the middle, or equator, of the spindle.  Each sister chromatid is attached to its own spindle fiber;  one sister chromatid's spindle fiber extends to one pole of the cell, the other sister chromatid's spindle fiber extends to the other.                  
For a drawing of a cell in Metaphase, please click on:www.ias.unt.edu/~tpp001/metaphase_text.JPG


ANAPHASE:  Separation of sister chromatids marks the beginning of Anaphase.  The centromeres split apart and chromatid pairs separate.  The microtubules in the spindle fibers shorten, pulling chromatids away from each other.
For a look at Anaphase, click on:www.biology.iupui.edu/biocourses/N100/images/8anaphase.gif



TELOPHASE:  Chromatids now reach opposite poles of the cell.  Much of Telophase is like Prophase in reverse.  Chromosomes begin to uncoil so they may again begin metabolic activities.  The mitotic spindle breaks down, the nucleolus reappears and a new nuclear envelope forms around each new set of chromosomes.  A new double membrane begins to form between the two nuclei.
See Telophase cell at: