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
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
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.
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
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.
All of the chromosomes line up across the center of the cell.
chromosomes separate. One copy of each chromosome is pulled to each
end of the cell by the spindle fibers
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.
for the two
new cells begins
The chromosomes uncoil and the
cells begin to grow.
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.
A large file but with a good audio narration
can be found at
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.)
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