Normal cell division may be observed in rapid growth stages. The examples displayed here are from the whitefish blastula.
Mitosis is the process whereby one parent cell divides to become two daughter cells, without changing the chromosome number in the process.
Growth--the cell grows in size.
S Phase of Cell Cycle:
Prior to mitosis, the cell readies itself by duplicating its chromosomes and other cellular contents.
The chromosomes at this stage are dispersed and not visible using a light microscope.
Before DNA synthesis, the cells chromosomes consist of one chromatid, called a monad.
After DNA synthesis, the cells chromosomes consist of dyads with 2 identical sister chromatids attached at the centromere.
G2 Phase of the Cell Cycle:
The cell prepares the enzymes and machinery for mitosis.
During early prophase, the chromosomes condense, making them distinguishable when using a light microscope.
The nuclear envelope disperses.
During late prophase, the nucleoli disappear and the mitotic spindle apparatus assembles.
The mitotic spindle will consist of microtubules that extend from pole to pole.
The mitotic spindle attaches to the centromere of each chromosome and moves them through the "dance of mitosis".
Note that the centromeres of each chromosome are aligned at the equator of the cell; the telomeres drift away from the equator.
During anaphase the mitotic spindle apparatus pulls the chromatids of each chromosome apart by attaching to each centromere. Note that the telomeres of each chromosome point toward the cells equator.
Chromosomes begin to disperse. Spindle fibers disperse. Cytokinesis begins--formation of daughter cells. In animals, like the whitefish, a cleavage furrow, a contractile ring of muscle like fibers, pinches the cell into two. The nuclear envelope forms again around the nuclei.
Normal Cell Division may be observed in onion root tips. Many of the processes are similar to those in animal cells. However, in plant cells, the cell plate between daughter cells forms from the golgi.
How many stages of mitosis can you identify in the above picture?
Significance of Mitosis
Mitosis results in exactly identical chromosomes in each daughter cell.
The number of chromosomes stays the same following mitosis:
a diploid cell produces diploid cells,
a haploid cell produces haploid cells.
This page was produced by Barbara Krumhardt, Ph.D., Science Group Leader, Biology Instructor, Urban Campus, Des Moines Area Community College, Des Moines, Iowa, USA 50314
Back to Urbans Biology Home Page