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 Mitosis  

 
The Dance of the Chromosomes  


When a human cell divides, its 46 chromosomes must be copied, or replicated, and each of the two new cells must receive only one copy of each chromosome.  Mitosis (from the Greek mitos = thread) is the process that sorts the genetic material into two new nuclei and ensures that both contain exactly the same genetic information.

Embryos, babies and children grow using mitosis, and mitosis occurs all the time in our adult bodies, as new cells replace old ones--such as worn-out blood cells or skin cells injured by cuts or burns. 

Though mitosis is a smooth continuous process, biologists have divided it into several stages. 

 Interphase

Interphase is the cell growth phase in which a cell increases in size and carries out activities that support the organism.  It is technically not a part of mitosis.  Near the end of this phase, the chromosomes of the cell duplicate in preparation for cell division.  By the time a cell is ready to divide, there are two copies of each chromosome (the sister chromatids.)   
 

 Prophase   Prophase Cell
The chromosomes coil, becoming short and thick. The nuclear membrane appears to dissolve and the chromosomes float in the cytoplasm.  The spindle, a football-shaped, cage like structure consisting of thin fibers forms in the cytoplasm.  The spindle fibers attach to the centromeres of the chromosomes and to both ends of the cell.
 

 Metaphase
Metaphase Cell
All of the chromosomes line up across the center of the cell.

 

 

 Anaphase

The chromosomes separate.  One copy of each chromosome is pulled to each end of the cell by the spindle fibers

 

 Telophase Telophase Cell

The cell membrane begins to pinch the cell in two to divide the cytoplasm.  A new nuclear membrane forms in each daughter cell. 

The daughter cells contain the same genetic information as was found in the original cell and as each other because the chromosomes in each cell are the same.   

 Interphase   for the two new cells begins

The chromosomes uncoil and the cells begin to grow.

Images from http://www.biodidac.bio.uottawa.ca  

For a more detailed discussion of mitosis with accompanying micrographs see:  http://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html

The best way to understand mitosis is to watch a cartoon animation, or better yet, a movie made through a microscope of the actual thing.  

I thank the owners of the Cytographics website at http://www.cytographics.com/gallery/clips/cg.html for permission to include the little QuickTime movie to the right.  Click on the picture to view mitosis and cell division in cultured animal tissue.

Link to Mitosis Movie
(750 K with audio)

Links to animations and movies of mitosis on other websites

The first link is a relatively small file (1.323 KB) with a text narrative but no audio.

http://tidepool.st.usm.edu/crswr/mitosismov.html

A large file but with a good audio narration can be found at

http://highered.mcgraw-hill.com/sites/0073031216/student_view0/exercise13/mitosis_movie.html.

The third length is a 9.68 MB movie of an actual cell undergoing mitosis.  Well worth it if you have a fast Internet connection (DSL, cable or satellite.)

http://www.fed.cuhk.edu.hk/~johnson/animations/cell_division/mitosis_movie_1.mov

And finally a 12 MB cartoon animation of mitosis with an audio narration.  Goes into more detail.  Kids don't try this without a fast connection!

http://www.fed.cuhk.edu.hk/~johnson/animations/cell_division/mitosis_movie_2.mov

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This web is lovingly dedicated to the memory of
Mr. James Dorsey
who so graciously and enthusiastically
donated his DNA to solve our family mystery. 


Jim Dorsey
2/12/1930 — 4-30-2002

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