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Not to be confused with meiosis, miosis, myositis, or myosotis.
Mitosis in an animal cell.
Mitosis divides the chromosomes in a cell nucleus.
a. non-dividing cells
b. nuclei preparing for division (spireme-stage)
c. dividing cells showing mitotic figures
e. pair of daughter-cells shortly after division

Mitosis is the process, in the cell cycle, by which the chromosomes in the cell nucleus are separated into two identical sets of chromosomes, each in its own nucleus. In general, mitosis is followed immediately by cytokinesis, which divides the cytoplasm, organelles, and cell membrane, and later karyokinesis, which divides the nucleus, dividing the cell into two new cells containing roughly equal shares of these cellular components.[1][unreliable source?] Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 20% of the cell cycle.

Mitosis occurs only in eukaryotic cells and the process varies in different groups.[2] For example, animals undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while fungi such as Aspergillus nidulans and Saccharomyces cerevisiae (yeast) undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus.[3] Prokaryotic cells, which lack a nucleus, divide by a process called binary fission.



Mitosis was discovered in frog, rabbit, and cat cornea cells in 1873 and described for the first time by the Polish histologist Wacław Mayzel in 1875.[6][7] The term is derived from the Greek word μίτος mitos "warp thread".[8][9]


Otto Bütschli was one of the first researchers who might have claimed the discovery of the process presently known as "mitosis",[10] a term coined by Walther Flemming in 1882.[11]

Overview of cell cycle in relation to mitosis[edit]

Time-lapse video of mitosis in a Drosophila melanogaster embryo.


The two identical chromatids resulting from chromatid duplication are called sister chromatids. They are held together by a specialized region of the chromosome: a DNA sequence called the centromere.

Mitosis begins when the chromosomes condense and become visible. In most eukaryotes, the nuclear membrane, which segregates the DNA from the cytoplasm, disintegrates into membrane vesicles. The nucleolus, which makes ribosomes in the cell, also dissolves. The chromosomes align themselves in a line spanning the cell. Microtubules splay out from opposite ends of the cell and shorten, pulling apart the sister chromatids of each chromosome.[13] Sister chromatids at this point are called daughter chromosomes. As the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends. A new nuclear membrane forms around the separated daughter chromosomes.


Prokaryotic cells undergo a process called binary fission, which is very much different from the process of mitosis, because there are no nuclear dynamics and chromosomes aren't linear.[14][clarification needed]

Phases of cell cycle and mitosis[edit]


The cell cycle
Main article: Interphase


Preprophase (plant cells)[edit]

Main article: Preprophase


Metaphase: The chromosomes align at the metaphase plate. 
Anaphase: The chromosomes split and the kinetochore microtubules shorten. 


Main article: Prophase

During this stage the cell prepares to divide by dissolving the membrane around the nucleus and the chromatin condenses into chromosomes. Normally, the genetic material in the nucleus is in a loosely bundled coil called chromatin. At the onset of prophase, chromatin fibers become tightly coiled, condensing into discrete chromosomes. It is crucial for the reader to note that chromatin is a complex consisting of both DNA and specific proteins. Since the genetic material has already been duplicated earlier in S phase, the replicated chromosomes have two sister chromatids, bound together at the centromere by the cohesin protein complex. Chromosomes are typically visible at high magnification through a light microscope.




Main article: Prometaphase

Note: Prometaphase is sometimes included as part of the end of prophase or part of early metaphase.

During early prometaphase, the nuclear membrane disintegrates and microtubules invade the nuclear space. This is called open mitosis, and it occurs in most multicellular organisms. Fungi and some protists, such as algae or trichomonads, undergo a variation called closed mitosis where the spindle forms inside the nucleus, or its microtubules are able to penetrate the nuclear membrane, which stays intact.[17][18]

In late prometaphase, each chromosome forms two kinetochores at its centromere, one attached at each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome.[19] Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor.[20] When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.[20]




Main article: Metaphase




Main article: Anaphase

When every kinetochore is attached to a cluster of microtubules and the chromosomes have lined up along the metaphase plate, the cell proceeds to anaphase (from the Greek word ανα meaning "up," "against," "back," or "re-").

Two events then occur: First, the proteins that bind sister chromatids together are cleaved. These sister chromatids now become separate daughter chromosomes, and are pulled apart by shortening kinetochore microtubules and move toward the respective centrosomes to which they are attached. The cleaved centromeres go first while the chromatids trail behind. They all look as if they are trying to grab at their partners, because they become shaped like a V.

Next, the polar microtubules shorten, pulling the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell. The force that causes the centrosomes to move toward the ends of the cell is still unknown, although there is a theory that suggests that the rapid assembly and breakdown of microtubules may cause this movement. At the end of anaphase the kinetochore microtubules all degrade.[24]


Main article: Telophase



Cilliate undergoing cytokinesis, with the cleavage furrow being clearly visible
Main article: Cytokinesis

Cytokinesis is often mistakenly thought to be the final part of telophase; however, cytokinesis is a separate process that begins at the same time as telophase. Cytokinesis is not, in the technical sense, even a phase of mitosis but rather a separate process, necessary for completing cell division. In animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching off the separated nuclei.[25] In both animal and plant cells, cell division is also driven by vesicles derived from the Golgi apparatus, which move along microtubules to the middle of the cell.[26] In plants, this structure coalesces into a cell plate at the center of the phragmoplast and develops into a cell wall, separating the two nuclei. The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a phycoplast microtubule array during cytokinesis.[27] Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks the end of the M-phase.



Mitosis occurs in the following circumstances:

Development and growth
The number of cells within an organism increases by mitosis. This is the basis of the development of a multicellular body from a single cell, i.e., zygote and also the basis of the growth of a multicellular body.
Cell replacement
In some parts of body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. New cells are formed by mitosis and so are exact copies of the cells being replaced. In like manner, RBCs (red blood cells) have short lifespan (only about 4 months) and new RBCs are formed by mitosis.
Asexual reproduction

Consequences of errors[edit]






Endomitosis is a variant of mitosis without nuclear or cellular division, resulting in cells with many copies of the same chromosome occupying a single nucleus. This process may also be referred to as endoreduplication and the cells as endoploid.[5] An example of a cell that goes through endomitosis is the megakaryocyte.[29]

Timeline in pictures[edit]


Early prophase: Nonkinetochore microtubules, shown as green strands, have established a matrix around the degrading nucleus, in blue. The green nodules are the centrosomes. 
Early prometaphase: The nuclear membrane has just degraded, allowing the microtubules to quickly interact with the kinetochores on the chromosomes, which have just condensed. 
Late metaphase: The centrosomes have moved to the poles of the cell and have established the mitotic spindle. The chromosomes, in light blue, have all assembled at the metaphase plate, except for one. 
Anaphase: Lengthening nonkinetochore microtubules push the two sets of chromosomes further apart. 

See also[edit]


  1. ^ Carter, J. Stein (2014-01-14). "Mitosis". 
  2. ^ Raikov, IB (1994). "The diversity of forms of mitosis in protozoa: A comparative review". European Journal of Protistology 30 (3): 253–69. doi:10.1016/S0932-4739(11)80072-6. 
  8. ^ "mitosis". Online Etymology Dictionary. 
  11. ^ Sharp, L.W. (1921). An Introduction To Cytology, p. 143, [2]. New York: McGraw Hill Book Company Inc.
  16. ^ Raven et al., 2005, pp. 58–67.

Cited texts[edit]

Further reading[edit]

  • Morgan, David L. (2007). The cell cycle: principles of control. London: Published by New Science Press in association with Oxford University Press. ISBN 0-9539181-2-2. 
  • Campbell, N. and Reece, J. (December 2001). "The Cell Cycle". Biology (6th ed.). San Francisco: Benjamin Cummings/Addison-Wesley. pp. 217–224. ISBN 0-8053-6624-5. 
  • Cooper, G. (2000). "The Events of M Phase". The Cell: A Molecular Approach. Sinaeur Associates, Inc. Retrieved 2006-01-22. 
  • Freeman, S (2002). "Cell Division". Biological Science. Upper Saddle River, NJ: Prentice Hall. pp. 155–174. ISBN 0-13-081923-9. 

External links[edit]