View source for Mitosis

{{Short description|Cell division into two identical cells}}
{{About||the type of cell division in sexually reproducing organisms used to produce gametes|Meiosis|excessive constriction of the pupils|Miosis|the parasitic infestation|Myiasis|muscle inflammation|Myositis}}
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[[File:Animal cell cycle-en.svg|thumb|upright=1.5|Mitosis in the animal [[cell cycle]] (phases ordered counter-clockwise).]]

'''Mitosis''' ({{IPAc-en|m|aɪ|ˈ|t|oʊ|s|ɪ|s}}) is a part of the [[cell cycle]] in [[eukaryote|eukaryotic cells]] in which replicated [[chromosome]]s are separated into two new [[Cell nucleus|nuclei]]. [[Cell division]] by mitosis is an equational division which gives rise to genetically identical cells in which the total number of chromosomes is maintained.<ref>{{cite web |url=https://www.britannica.com/science/cell-biology/Cell-division-and-growth |title=Cell division and growth |website=britannica.com |publisher=ENCYCLOPÆDIA BRITANNICA |access-date=2018-11-04 |archive-url=https://web.archive.org/web/20181028112924/https://www.britannica.com/science/cell-biology/Cell-division-and-growth |archive-date=2018-10-28 |url-status=live }}</ref> Mitosis is preceded by the [[S phase]] of [[interphase]] (during which [[DNA replication]] occurs) and is followed by [[telophase]] and [[cytokinesis]], which divide the [[cytoplasm]], [[organelle]]s, and [[cell membrane]] of one cell into two new [[cell (biology)|cells]] containing roughly equal shares of these cellular components.<ref>{{cite web |last= Carter |first= J. Stein | name-list-style = vanc |date= 2014-01-14 |title= Mitosis |url= http://biology.clc.uc.edu/courses/bio104/mitosis.htm |website= biology.clc.uc.edu |archive-url= https://web.archive.org/web/20121027084115/http://biology.clc.uc.edu/courses/bio104/mitosis.htm |archive-date= 2012-10-27 |access-date= 2019-11-12 }}</ref> This process ensures that each daughter cell receives an identical set of chromosomes, maintaining genetic stability across cell generations. The different stages of mitosis altogether define the '''mitotic phase''' (M phase) of a cell cycle—the [[cell division|division]] of the mother cell into two daughter cells genetically identical to each other.<ref>{{cite book |doi=10.1016/B978-0-12-812100-9.00018-8 |chapter=Cell-Cycle Regulation |title=Handbook of Brain Tumor Chemotherapy, Molecular Therapeutics, and Immunotherapy |date=2018 |last1=Figel |first1=Sheila |last2=Fenstermaker |first2=Robert A. |pages=257–269 |isbn=978-0-12-812100-9 }}</ref>

The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are [[preprophase]] (specific to plant cells), [[prophase]], [[prometaphase]], [[metaphase]], [[anaphase]], and [[telophase]]. During mitosis, the chromosomes, which have already duplicated during  interphase, condense and attach to [[spindle apparatus|spindle fibers]] that pull one copy of each chromosome to opposite sides of the cell.<ref>{{Cite web|title = Cell Division: Stages of Mitosis {{!}} Learn Science at Scitable|url = http://www.nature.com/scitable/topicpage/mitosis-and-cell-division-205#|website = www.nature.com|access-date = 2015-11-16|url-status = live|archive-url = https://web.archive.org/web/20151114201118/http://www.nature.com/scitable/topicpage/mitosis-and-cell-division-205|archive-date = 2015-11-14}}</ref> The result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells.<ref name="Maton-1997"/> The different phases of mitosis can be visualized in real time, using [[live cell imaging]].<ref>{{cite journal |last1=Sandoz |first1=Patrick A. | name-list-style = vanc |title=Image-based analysis of living mammalian cells using label-free 3D refractive index maps reveals new organelle dynamics and dry mass flux |journal=PLOS Biology |date=December 2019 |volume=17 |issue=12 |article-number=e3000553 |doi=10.1371/journal.pbio.3000553 |pmid=31856161 |pmc=6922317 |doi-access=free }}</ref>

An error in mitosis can result in the production of three or more daughter cells instead of the normal two. This is called tripolar mitosis and multipolar mitosis, respectively. These errors can be the cause of non-viable embryos that fail to [[Implantation (embryology)|implant]].<ref name="Kalatova-2015">{{cite journal | vauthors = Kalatova B, Jesenska R, Hlinka D, Dudas M | title = Tripolar mitosis in human cells and embryos: occurrence, pathophysiology and medical implications | journal = Acta Histochemica | volume = 117 | issue = 1 | pages = 111–25 | date = January 2015 | pmid = 25554607 | doi = 10.1016/j.acthis.2014.11.009 | doi-access = free }}</ref> Other errors during mitosis can induce [[mitotic catastrophe]], [[apoptosis]] (programmed cell death) or cause [[mutation]]s. Certain types of [[cancers]] can arise from such mutations.<ref>{{cite journal | vauthors = Kops GJ, Weaver BA, Cleveland DW | title = On the road to cancer: aneuploidy and the mitotic checkpoint | journal = Nature Reviews. Cancer | volume = 5 | issue = 10 | pages = 773–85 | date = October 2005 | pmid = 16195750 | doi = 10.1038/nrc1714 }}</ref>

Mitosis varies between organisms.<ref name="Raikov-1994"/> For example, [[animal]] cells generally undergo an open mitosis, where the [[nuclear envelope]] breaks down before the chromosomes separate, whereas [[Fungus|fungal cells]] generally undergo a closed mitosis, where chromosomes divide within an intact cell nucleus.<ref name="De Souza-2007"/><ref name="Boettcher-2013">{{cite journal |vauthors=Boettcher B, Barral Y |title=The cell biology of open and closed mitosis |journal=Nucleus |volume=4 |issue=3 |pages=160–5 |date=2013 |pmid=23644379 |pmc=3720745 |doi=10.4161/nucl.24676 |url=}}</ref> Most animal cells undergo a shape change, known as [[mitotic cell rounding]], to adopt a near spherical morphology at the start of mitosis. Most human cells are produced by mitotic cell division. Important exceptions include the [[gamete]]s – [[sperm]] and [[ovum|egg]] cells – which are produced by [[meiosis]]. [[Prokaryote]]s, bacteria and archaea which lack a true nucleus, divide by a different process called [[binary fission]].<ref>{{Cite book |last=Patil |first=C. s |url=https://books.google.com/books?id=xuNSaqmj7xMC&dq=Mitosis+occurs+only+in+eukaryotic+cells.+Prokaryotic+cells%2C+which+lack+a+nucleus%2C+divide+by+a+different+process+called+binary+fission&pg=PA129 |title=Cell Biology |publisher=APH Publishing |isbn=978-81-313-0416-7 |language=en}}</ref>

== Discovery ==
Numerous descriptions of [[cell division]] were made during 18th and 19th centuries, with various degrees of accuracy.<ref name="Ross"/> In 1835, the German botanist [[Hugo von Mohl]], described cell division in the [[green algae]] ''[[Cladophora|Cladophora glomerata]]'', stating that multiplication of cells occurs through cell division.<ref>{{cite thesis | vauthors = von Mohl H | date = 1835 | title = Ueber die Vermehrung der Pflanzenzellen durch Theilung| work = Inaugural-Dissertation | publisher = Tübingen | url = https://books.google.com/books?id=vHRSAAAAcAAJ }}</ref><ref>{{NDB|17|690|691|Mohl, Hugo von|Karl Mägdefrau|118830538}}</ref><ref>"Notes and memoranda: The late professor von Mohl". ''Quarterly Journal of Microscopical Science'', v. XV, New Series, p. 178–181, 1875. [https://books.google.com/books?id=Yg5LAAAAYAAJ link].</ref> In 1838, [[Matthias Jakob Schleiden]] affirmed that "formation of new cells ''in their interior'' was a general rule for cell multiplication in plants", a view later rejected in favour of Mohl's model, due to contributions of [[Robert Remak]] and others.<ref>{{cite journal |last1=Weyers |first1=Wolfgang |title=Screening for malignant melanoma—a critical assessment in historical perspective |journal=Dermatology Practical & Conceptual |date=30 April 2018 |volume=8 |issue=2 |pages=89–103 |doi=10.5826/dpc.0802a06 |pmid=29785325 |pmc=5955075 }}</ref>

In animal cells, cell division with 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.<ref>{{cite journal| first = Janusz | last = Komender | name-list-style = vanc |year= 2008|title= Kilka słów o doktorze Wacławie Mayzlu i jego odkryciu|language= pl|trans-title= On Waclaw Mayzel and his observation of mitotic division|journal= Postępy Biologii Komórki|volume= 35|issue= 3|pages= 405–407|url= http://ptbk.mol.uj.edu.pl/download/historie_z_przeszlosci/Waclaw%20Mayzel.pdf|url-status= live|archive-url= https://web.archive.org/web/20121027145052/http://ptbk.mol.uj.edu.pl/download/historie_z_przeszlosci/Waclaw%20Mayzel.pdf|archive-date= 2012-10-27}}</ref><ref>{{cite book |title=Dzieje nauki polskiej|last= Iłowiecki|first=Maciej | name-list-style = vanc | year=1981|publisher=Wydawnictwo Interpress|location= Warszawa|page= 187|isbn=978-83-223-1876-8}}</ref>

Bütschli, Schneider and Fol might have also claimed the discovery of the process presently known as "mitosis".<ref name="Ross">Ross, Anna E. "Human Anatomy & Physiology I: A Chronology of the Description of Mitosis". ''Christian Brothers University''. Retrieved 02 May 2018. [http://facstaff.cbu.edu/~aross/AP-I/Mitosis-Chronology.html#chronology link] {{Webarchive|url=https://web.archive.org/web/20160512000047/http://facstaff.cbu.edu/~aross/AP-I/Mitosis-Chronology.html#chronology |date=2016-05-12 }}.</ref> In 1873, the German zoologist [[Otto Bütschli]] published data from observations on [[nematode]]s. A few years later, he discovered and described mitosis based on those observations.<ref>Bütschli, O. (1873). Beiträge zur Kenntnis der freilebenden Nematoden. ''Nova Acta der Kaiserlich Leopoldinisch-Carolinischen Deutschen Akademie der Naturforscher'' 36, 1–144. [https://www.biodiversitylibrary.org/item/45422#page/443/mode/1up link] {{Webarchive|url=https://web.archive.org/web/20180811015718/https://www.biodiversitylibrary.org/item/45422#page/443/mode/1up |date=2018-08-11 }}.</ref><ref>Bütschli, O. (1876). Studien über die ersten Entwicklungsvorgänge der Eizelle, die Zelleilung und die Conjugation der Infusorien. ''Abh.d. Senckenb. Naturf. Ges. Frankfurt a. M.'' 10, 213–452. [https://www.biodiversitylibrary.org/item/187692#page/277/mode/1up link] {{Webarchive|url=https://web.archive.org/web/20180809112726/https://www.biodiversitylibrary.org/item/187692#page/277/mode/1up |date=2018-08-09 }}.</ref><ref>{{cite journal | vauthors = Fokin SI | year = 2013 | title = Otto Bütschli (1848–1920) Where we will genuflect? | url = http://protistology.ifmo.ru/num8_1/fokin_protistology_8-1.pdf | journal = Protistology | volume = 8 | issue = 1 | pages = 22–35 | access-date = 2014-08-06 | archive-url = https://web.archive.org/web/20140808063603/http://protistology.ifmo.ru/num8_1/fokin_protistology_8-1.pdf | archive-date = 2014-08-08 | url-status = live }}</ref>

The term "mitosis", coined by [[Walther Flemming]] in 1882,<ref>{{cite book | vauthors = Sharp LW |year=1921 |url=https://archive.org/stream/introductiontocy032473mbp#page/n155/mode/2upAn |title=Introduction To Cytology |page=143 |location=New York |publisher=McGraw Hill Book Company Inc.}}</ref> is derived from the [[Greek language|Greek]] word μίτος (''mitos'', "warp thread").<ref name="mitosis">{{cite encyclopedia|title=mitosis|url=http://www.etymonline.com/index.php?term=mitosis&allowed_in_frame=0|dictionary=[[Online Etymology Dictionary]]|access-date=2019-11-12|archive-url=https://web.archive.org/web/20170928005443/http://www.etymonline.com/index.php?term=mitosis&allowed_in_frame=0|archive-date=2017-09-28|url-status=live }}</ref><ref name="Liddell">{{LSJ|mi/tos|μίτος|ref}}</ref> There are some alternative names for the process,<ref>{{cite journal | vauthors = Battaglia E | date = 2009 | title = Caryoneme alternative to chromosome and a new caryological nomenclature. | journal = Caryologia | volume = 62 | issue = 4 | pages = 1–80 | url = http://www.caryologia.unifi.it/past_volumes/62_4supplement/62-4_supplement.pdf | archive-url = https://web.archive.org/web/20160304032405/http://www.caryologia.unifi.it/past_volumes/62_4supplement/62-4_supplement.pdf | archive-date=2016-03-04 }}</ref> e.g., "karyokinesis" (nuclear division), a term introduced by Schleicher in 1878,<ref>{{cite journal | vauthors = Schleicher W | date = 1878 | title = Die Knorpelzelltheilung | journal = Arch. Mirkroskop. Anat. | volume = 16 | pages = 248–300 | doi = 10.1007/BF02956384 | url = https://www.biodiversitylibrary.org/item/49519#page/258/mode/1up | archive-url = https://web.archive.org/web/20180811030026/https://www.biodiversitylibrary.org/item/49519#page/258/mode/1up | archive-date=2018-08-11 }}</ref><ref>{{cite web | vauthors = Toepfer G | title = Karyokinesis | work = BioConcepts | access-date = 2 May 2018 | url = http://www.biological-concepts.com/views/search.php?term=1770&listed=y | archive-url = https://web.archive.org/web/20180503180225/http://www.biological-concepts.com/views/search.php?term=1770&listed=y | archive-date=2018-05-03 }}</ref> or "equational division", proposed by [[August Weismann]] in 1887.<ref>{{cite journal | vauthors = Battaglia E | date = 1987 | title = Embryological questions: 12. Have the ''Polygonum'' and ''Allium'' types been rightly established? | journal = Ann Bot | location = Rome | volume = 45 | pages = 81–117 | quote = p. 85: Already in 1887, Weismann gave the names ''Aequationstheilung'' to the usual cell division, and ''Reduktionstheilungen'' to the two divisions involved in the halving process of the number of ''Kernsegmente'' }}</ref> However, the term "mitosis" is also used in a broad sense by some authors to refer to karyokinesis and cytokinesis together.<ref>{{cite book | vauthors = Mauseth JD | date = 1991 | title = Botany: an Introduction to Plant Biology | publisher = Saunders College Publishing | location = Philadelphia | isbn = 978-0-03-030222-0 | quote = p. 102: Cell division is cytokinesis, and nuclear division is karyokinesis. The words "mitosis" and "meiosis" technically refer only to karyokinesis but are frequently used to describe cytokinesis as well. | url = https://books.google.com/books?id=npUoAQAAMAAJ }}</ref> Presently, "equational division" is more commonly used to refer to [[meiosis II]], the part of meiosis most like mitosis.<ref>{{Cite journal|last=Cooper|first=Geoffrey M.|date=2000|title=Meiosis and Fertilization|url=https://www.ncbi.nlm.nih.gov/books/NBK9901/|journal=The Cell: A Molecular Approach. 2nd Edition|language=en}}</ref>

==Phases==
{{Main|Cell cycle}}

===Overview===
[[File:Mitosis drosophila larva.ogv|thumb|150px|right|Time-lapse video of mitosis in a ''[[Drosophila melanogaster]]'' [[embryo]]]]
The primary result of mitosis and cytokinesis is the transfer of a parent cell's [[genome]] into two daughter cells. The genome is composed of a number of chromosomes—complexes of tightly coiled [[DNA]] that contain [[DNA sequence|genetic information]] vital for proper cell function.<ref>{{cite book |last1=Brown |first1=Terence A. |title=Genomes |date=2002 |publisher=Wiley-Liss |edition=2nd |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK21134/ |chapter=The Human Genome }}</ref> Because each resultant daughter cell should be [[clone (genetics)|genetically identical]] to the parent cell, the parent cell must make a copy of each chromosome before mitosis. This occurs during the [[S phase]] of interphase.<ref name="Blow-2005"/> [[DNA replication|Chromosome duplication]] results in two identical ''[[sister chromatids]]'' bound together by [[cohesin]] proteins at the ''[[centromere]]''.

When mitosis begins, the chromosomes condense and become visible. In some eukaryotes, for example animals, the [[nuclear envelope]], which segregates the DNA from the cytoplasm, disintegrates into small vesicles. The [[nucleolus]], which makes ribosomes in the cell, also disappears. [[Microtubule]]s project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within the cell. The microtubules then contract to pull the sister chromatids of each chromosome apart.<ref name="Zhou-2002"/> Sister chromatids at this point are called ''daughter chromosomes''. As the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase. A new nuclear envelope forms around each set of daughter chromosomes, which decondense to form interphase nuclei.

During mitotic progression, typically after the anaphase onset, the cell may undergo cytokinesis. In [[animal cell]]s, a [[cleavage furrow|cell membrane pinches inward]] between the two developing nuclei to produce two new cells. In [[plant cell]]s, a [[cell plate]] forms between the two nuclei. Cytokinesis does not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis.

{{wide image|Mitosis Stages.svg|1100px|Diagram of [[interphase]] and the following five mitotic stages of the M phase including [[cytokinesis]].}}

===Interphase===
<!-- that graph and the following paragraph must have full labels not just single letters -->
{{main|Interphase}}
The interphase is a much longer phase of the [[cell cycle]] than the relatively short M phase. During interphase the cell prepares itself for the process of cell division. Interphase is divided into three subphases: [[G1 phase|G<sub>1</sub> (first gap)]], [[S phase|S (synthesis)]], and [[G2 phase|G<sub>2</sub> (second gap)]]. During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the [[S phase]]. Thus, a cell grows (G<sub>1</sub>), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G<sub>2</sub>), and finally divides (M) before restarting the cycle.<ref name="Blow-2005"/> All these phases in the cell cycle are highly regulated by [[cyclins]], [[cyclin-dependent kinases]], and other cell cycle proteins. The phases follow one another in strict order and there are [[cell cycle checkpoint]]s that give the cell cues to proceed or not, from one phase to another.<ref>{{cite web |last1=Biology Online |title= Mitosis |url=https://www.biologyonline.com/dictionary/mitosis |website=Biology Online|date= 28 April 2020 }}</ref> Cells may also temporarily or permanently leave the cell cycle and enter [[G0 phase|G<sub>0</sub> phase]] to stop dividing. This can occur when cells become overcrowded ([[density-dependent inhibition]]) or when they [[Cellular differentiation|differentiate]] to carry out specific functions for the organism, as is the case for [[Cardiac muscle cell|human heart muscle cells]] and [[neurons]]. Some G<sub>0</sub> cells have the ability to re-enter the cell cycle.

DNA double-strand breaks can be [[DNA repair|repaired]] during interphase by two principal processes.<ref>{{cite journal | pmid = 28781144 | doi=10.1016/j.mrfmmm.2017.07.011 | volume=803-805 | title=Regulation of repair pathway choice at two-ended DNA double-strand breaks | year=2017 | journal=Mutat Res | pages=51–55  | vauthors = Shibata A | bibcode=2017MRFMM.803...51S }}</ref>  The first process, [[non-homologous end joining]] (NHEJ), can join the two broken ends of DNA in the [[G1 phase|G1]], [[S phase|S]] and [[G2 phase|G2]] phases of interphase.  The second process, [[homologous recombination]]al repair (HRR), is more accurate than NHEJ in repairing double-strand breaks.  HRR is active during the S and G2 phases of interphase when [[DNA replication]] is either partially accomplished or after it is completed, since HRR requires two adjacent [[chromatids|homologs]].

Interphase helps prepare the cell for mitotic division. It dictates whether the mitotic cell division will occur. It carefully stops the cell from proceeding whenever the cell's DNA is damaged or has not completed an important phase. The interphase is very important as it will determine if mitosis completes successfully. It will reduce the amount of damaged cells produced and the production of cancerous cells. A miscalculation by the key Interphase proteins could be crucial as the latter could potentially create cancerous cells.<ref>{{cite journal |last1=Bernat |first1=R L |last2=Borisy |first2=G G |last3=Rothfield |first3=N F |last4=Earnshaw |first4=W C |title=Injection of anticentromere antibodies in interphase disrupts events required for chromosome movement at mitosis |journal=The Journal of Cell Biology |date=October 1990 |volume=111 |issue=4 |pages=1519–1533 |doi=10.1083/jcb.111.4.1519 |pmid=2211824 |pmc=2116233 }}</ref>

===Mitosis===
[[File:Stages of early mitosis in a vertebrate cell with micrographs of chromatids.svg|thumb|right|Stages of early mitosis in a vertebrate cell with [[micrograph]]s of [[chromatid]]s]]

====Preprophase (plant cells)====
{{main|Preprophase}}
In plant cells only, prophase is preceded by a [[preprophase]] stage. In highly [[vacuole|vacuolated]] plant cells, the nucleus has to migrate into the center of the cell before mitosis can begin. This is achieved through the formation of a [[phragmosome]], a transverse sheet of cytoplasm that bisects the cell along the future plane of cell division. In addition to phragmosome formation, preprophase is characterized by the formation of a ring of microtubules and [[actin]] filaments (called [[preprophase band]]) underneath the plasma membrane around the equatorial plane of the future mitotic [[spindle apparatus|spindle]]. This band marks the position where the cell will eventually divide. The cells of higher plants (such as the [[flowering plant]]s) lack [[centrioles]]; instead, microtubules form a spindle on the surface of the nucleus and are then organized into a spindle by the chromosomes themselves, after the nuclear envelope breaks down.<ref name="Lloyd-2006"/> The preprophase band disappears during nuclear envelope breakdown and spindle formation in prometaphase.<ref name="Raven-2005">{{cite book | vauthors = Raven PH, Evert RF, Eichhorn SE |title= Biology of Plants |url= https://archive.org/details/biologyofplants00rave_0 |url-access= registration |edition= 7th |publisher= [[W. H. Freeman and Company|W. H. Freeman and Co.]] |year= 2005 |location= New York |isbn= 978-0-7167-1007-3}}</ref>{{rp|58–67}}

====Prophase====
{{main|Prophase}}
[[File:CONDENSING CHROMOSOMES 2.jpg|thumb|left|Interphase nucleus (left), condensing chromosomes (middle) and condensed chromosomes (right)]]

[[File:Prophase diagram.svg|thumb|[[Prophase]] during mitosis]]

During prophase, which occurs after G<sub>2</sub> interphase, the cell prepares to divide by tightly condensing its chromosomes and initiating mitotic spindle formation. During interphase, the genetic material in the nucleus consists of loosely packed [[chromatin]]. At the onset of prophase, chromatin fibers condense into discrete chromosomes that are typically visible at high magnification through a [[light microscope]]. In this stage, chromosomes are long, thin, and thread-like. Each chromosome has two chromatids. The two chromatids are joined at the centromere.

[[Gene transcription]] ceases during prophase and does not resume until late anaphase to early G<sub>1</sub> phase.<ref>{{cite journal | vauthors = Prasanth KV, Sacco-Bubulya PA, Prasanth SG, Spector DL | title = Sequential entry of components of the gene expression machinery into daughter nuclei | journal = Molecular Biology of the Cell | volume = 14 | issue = 3 | pages = 1043–57 | date = March 2003 | pmid = 12631722 | pmc = 151578 | doi = 10.1091/mbc.E02-10-0669 }}</ref><ref>
{{cite journal | vauthors = Kadauke S, Blobel GA | title = Mitotic bookmarking by transcription factors | journal = Epigenetics & Chromatin | volume = 6 | issue = 1 | page = 6 | date = April 2013 | pmid = 23547918 | pmc = 3621617 | doi = 10.1186/1756-8935-6-6 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Prescott DM, Bender MA | title = Synthesis of RNA and protein during mitosis in mammalian tissue culture cells | journal = Experimental Cell Research | volume = 26 | issue = 2 | pages = 260–8 | date = March 1962 | pmid = 14488623 | doi = 10.1016/0014-4827(62)90176-3 }}</ref> The [[nucleolus]] also disappears during early prophase.<ref>{{cite book | vauthors = Olson MO | date=2011 |title=The Nucleolus |volume=15 of Protein Reviews |location=Berlin |publisher=Springer Science & Business Media |page=15 |isbn=978-1-4614-0514-6 }}</ref>

Close to the nucleus of an animal cell are structures called [[centrosome]]s, consisting of a pair of [[centriole]]s surrounded by a [[Pericentriolar material|loose collection of proteins]]. The centrosome is the coordinating center for the cell's [[microtubule]]s. A cell inherits a single centrosome at cell division, which is [[Centrosome cycle|duplicated by the cell]] before a new round of mitosis begins, giving a pair of centrosomes. The two centrosomes polymerize [[tubulin]] to help form a [[spindle apparatus|microtubule spindle apparatus]]. [[Motor proteins]] then push the centrosomes along these microtubules to opposite sides of the cell. Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle apparatus, since they are absent from plants,<ref name="Lloyd-2006"/> and are not absolutely required for animal cell mitosis.<ref name="Basto-2006">{{cite journal | vauthors = Basto R, Lau J, Vinogradova T, Gardiol A, Woods CG, Khodjakov A, Raff JW | title = Flies without centrioles | journal = Cell | volume = 125 | issue = 7 | pages = 1375–86 | date = June 2006 | pmid = 16814722 | doi = 10.1016/j.cell.2006.05.025 | doi-access = free }}</ref>

====Prometaphase====
{{main|Prometaphase}}
At the beginning of prometaphase in animal cells, phosphorylation of [[lamin|nuclear lamins]] causes the [[nuclear envelope]] to disintegrate into small membrane [[Vesicle (biology and chemistry)|vesicles]]. As this happens, microtubules invade the nuclear space. This is called ''open mitosis'', and it occurs in some multicellular organisms. Fungi and some [[protist]]s, such as [[algae]] or [[trichomonad]]s, undergo a variation called ''closed mitosis'' where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope.<ref name="Heywood-1978"/><ref name="Ribeiro-2002"/>

In late prometaphase, ''kinetochore microtubules'' begin to search for and attach to chromosomal [[kinetochores]].<ref name="Chan-2005"/> A ''kinetochore'' is a [[protein]]aceous microtubule-binding structure that forms on the chromosomal centromere during late prophase.<ref name="Chan-2005"/><ref>{{cite journal | vauthors = Cheeseman IM, Desai A | title = Molecular architecture of the kinetochore-microtubule interface | journal = Nature Reviews. Molecular Cell Biology | volume = 9 | issue = 1 | pages = 33–46 | date = January 2008 | pmid = 18097444 | doi = 10.1038/nrm2310 }}</ref> A number of ''polar microtubules'' find and interact with corresponding polar microtubules from the opposite centrosome to form the mitotic spindle.<ref name="Winey-1995"/> Although the kinetochore structure and function are not fully understood, it is known that it contains some form of [[List of gene families#Motor proteins|molecular motor]].<ref name="Maiato-2004"/> When a microtubule connects with the kinetochore, the motor activates, using energy from [[Adenosine triphosphate|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.<ref name="Maiato-2004"/>

====Metaphase====
[[File:Mitosis-fluorescent.jpg|thumb|right|A cell in late [[metaphase]]. All chromosomes (blue) but one have arrived at the [[metaphase plate]].]] 
{{main|Metaphase}}

[[File:Metaphase during Mitosis.svg|thumb|[[Metaphase]] during mitosis]]

After the microtubules have located and attached to the kinetochores in prometaphase, the two centrosomes begin pulling the chromosomes towards opposite ends of the cell. The resulting tension causes the chromosomes to align along the [[metaphase plate]] at the equatorial plane, an imaginary line that is centrally located between the two centrosomes (at approximately the midline of the cell).<ref name="Winey-1995"/> To ensure equitable distribution of chromosomes at the end of mitosis, the ''[[spindle checkpoint|metaphase checkpoint]]'' guarantees that kinetochores are properly attached to the mitotic spindle and that the chromosomes are aligned along the metaphase plate.<ref name="Chan-2003"/> If the cell successfully passes through the metaphase checkpoint, it proceeds to anaphase.

====Anaphase====
{{main|Anaphase}}

[[File:Anaphase during Mitosis.svg|thumb|[[Anaphase]] during mitosis]]

During ''anaphase A'', the [[cohesin]]s that bind sister chromatids together are cleaved, forming two identical daughter chromosomes.<ref name="FitzHarris-2012"/> Shortening of the kinetochore microtubules pulls the newly formed daughter chromosomes to opposite ends of the cell. During ''anaphase B'', polar microtubules push against each other, causing the cell to elongate.<ref name="Miller-2000"/> In late anaphase, [[chromosome]]s also reach their overall maximal condensation level, to help [[chromosome segregation]] and the re-formation of the nucleus.<ref>{{cite press release |title=Researchers Shed Light On Shrinking Of Chromosomes |url=https://www.sciencedaily.com/releases/2007/06/070611122252.htm |work=ScienceDaily |publisher=European Molecular Biology Laboratory |date=12 June 2007 }}</ref> In most animal cells, anaphase A precedes anaphase B, but some vertebrate egg cells demonstrate the opposite order of events.<ref name="FitzHarris-2012">{{cite journal | vauthors = FitzHarris G | title = Anaphase B precedes anaphase A in the mouse egg | journal = Current Biology | volume = 22 | issue = 5 | pages = 437–44 | date = March 2012 | pmid = 22342753 | doi = 10.1016/j.cub.2012.01.041 | doi-access = free | bibcode = 2012CBio...22..437F }}</ref>

====Telophase====
{{main|Telophase}}

[[File:Telophase during Mitosis.svg|thumb|[[Telophase]] during mitosis]]

Telophase (from the [[Greek language|Greek]] word ''τελος'' meaning "end") is a reversal of prophase and prometaphase events. At telophase, the polar microtubules continue to lengthen, elongating the cell even more. If the nuclear envelope has broken down, a new nuclear envelope forms using the membrane vesicles of the parent cell's old nuclear envelope. The new envelope forms around each set of separated daughter chromosomes (though the membrane does not enclose the centrosomes) and the nucleolus reappears. Both sets of chromosomes, now surrounded by new nuclear membrane, begin to "relax" or decondense. Mitosis is complete. Each daughter nucleus has an identical set of chromosomes. Cell division may or may not occur at this time depending on the organism.

===Cytokinesis===
{{main|Cytokinesis}}

[[File:Cytokinesis illustration.svg|thumb|right|Cytokinesis illustration]]
[[File:Unk.cilliate.jpg|thumb|left|[[Ciliate]] undergoing [[cytokinesis]], with the [[cleavage furrow]] being clearly visible]]

[[Cytokinesis]] is not 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.<ref name="Glotzer-2005"/> 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.<ref name="Albertson-2005"/> 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.<ref name="Raven-2005"/>{{rp|64–7, 328–9}} 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.

There are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. The most notable occurrence of this is among the [[fungus|fungi]], [[slime mold]]s, and coenocytic algae, but the phenomenon is found in various other organisms. Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of [[Drosophila melanogaster|fruit fly]] embryonic development.<ref name="Lilly-2005"/>

== Function ==
The function or significance of mitosis, is the maintenance of the chromosomal set; each formed cell receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell.

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 the body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones.<ref>{{Cite book |last=Sunderland |title=The Cell: A Molecular Approach. 2nd edition. |publisher=Sinauer Associates |year=2000 |edition=2nd}}</ref> New cells are formed by mitosis and so are exact copies of the cells being replaced. In like manner, [[red blood cells]] have a short lifespan (only about 3 months) and new RBCs are formed by mitosis.<ref>{{Cite journal |last=Franco |first=Robert |date=27 August 2012 |title=Measurement of Red Cell Lifespan and Aging |journal=Transfusion Medicine and Hemotherapy |volume=39 |issue=5 |pages=302–307 |doi=10.1159/000342232 |pmid=23801920 |pmc=3678251 }}</ref>
*Regeneration: Some organisms can regenerate body parts. The production of new cells in such instances is achieved by mitosis. For example, [[starfish]] regenerate lost arms through mitosis.
*Asexual reproduction: Some organisms produce genetically similar offspring through [[asexual reproduction]]. For example, the [[hydra (genus)|hydra]] reproduces asexually by budding. The cells at the surface of hydra undergo mitosis and form a mass called a bud. Mitosis continues in the cells of the bud and this grows into a new individual. The same division happens during asexual reproduction or [[vegetative propagation]] in plants.

==Variations==
=== Forms of mitosis ===
The mitosis process in the cells of eukaryotic organisms follows a similar pattern, but with variations in three main details. "Closed" and "open" mitosis can be distinguished on the basis of [[nuclear envelope]] remaining intact or breaking down. An intermediate form with partial degradation of the nuclear envelope is called "semiopen" mitosis. With respect to the symmetry of the [[spindle apparatus]] during metaphase, an approximately axially symmetric (centered) shape is called "orthomitosis", distinguished from the eccentric spindles of "pleuromitosis", in which mitotic apparatus has bilateral symmetry. Finally, a third criterion is the location of the [[central spindle]] in case of closed pleuromitosis: "extranuclear" (spindle located in the cytoplasm) or "intranuclear" (in the nucleus).<ref name="Raikov-1994"/>

<gallery mode="nolines">
File:Mitosis classification closed intranuclear pleuromitoses.svg|closed <br /> intranuclear <br /> pleuromitosis
File:Mitosis classification closed extranuclear pleuromitoses.svg|closed <br /> extranuclear <br /> pleuromitosis
File:Mitosis classification closed orthomitoses.svg|closed <br /> orthomitosis
File:Mitosis classification semiopen pleuromitoses.svg|semiopen <br /> pleuromitosis
File:Mitosis classification semiopen orthomitoses.svg|semiopen <br /> orthomitosis
File:Mitosis classification open orthomitoses.svg|open <br /> orthomitosis
</gallery>

Nuclear division takes place only in cells of organisms of the [[eukaryotic]] domain, as [[bacteria]] and [[archaea]] have no nucleus. Bacteria and archaea undergo a different type of division.<ref>{{Cite web |last=Hogan |date=August 23, 2011 |title=Archaea |url=https://eol.org/docs/discover/archaea |website=Encyclopedia of Life}}</ref><ref>{{Cite web |title=Binary Fission and other Forms of Reproduction in Bacteria |url=https://cals.cornell.edu/microbiology/research/active-research-labs/angert-lab/epulopiscium/binary-fission-and-other-forms-reproduction-bacteria |website=Cornell College of Agriculture and Life Sciences}}</ref> Within each of the eukaryotic [[Eukaryote#Five supergroups|supergroups]], mitosis of the open form can be found, as well as closed mitosis, except for unicellular [[Excavata]], which show exclusively closed mitosis.<ref>{{cite journal | vauthors = Boettcher B, Barral Y | title = The cell biology of open and closed mitosis | journal = Nucleus | volume = 4 | issue = 3 | pages = 160–5 | year = 2013 | pmid = 23644379 | pmc = 3720745 | doi = 10.4161/nucl.24676 }}</ref> Following, the occurrence of the forms of mitosis in eukaryotes:<ref name="Raikov-1994"/><ref>R. Desalle, B. Schierwater: ''Key Transitions in Animal Evolution.'' CRC Press, 2010, p. 12, [https://books.google.com/books?id=LYDRBQAAQBAJ&pg=PA12 link] {{Webarchive|url=https://web.archive.org/web/20190102095006/https://books.google.de/books?id=LYDRBQAAQBAJ&lpg=PP1&hl=en&pg=PA12 |date=2019-01-02 }}.</ref>

*'''''Closed intranuclear pleuromitosis''''' is typical of [[Foraminifera]], some [[Prasinophyceae|Prasinomonadida]], some [[Kinetoplastida]], the [[Oxymonadida]], the [[Haplosporidia]], many fungi ([[chytrid]]s, [[oomycete]]s, [[zygomycete]]s, [[ascomycete]]s), and some [[Radiolaria]] ([[Spumellaria]] and [[Acantharea|Acantharia]]); it seems to be the most primitive type.
*'''''Closed extranuclear pleuromitosis''''' occurs in [[Trichomonadida]] and [[Dinoflagellata]].
* '''''Closed orthomitosis''''' is found among [[diatom]]s, [[ciliate]]s, some [[Microsporidia]], unicellular [[yeast]]s and some multicellular [[fungi]].
*'''''Semiopen pleuromitosis''''' is typical of most [[Apicomplexa]].
*'''''Semiopen orthomitosis''''' occurs with different variants in some amoebae ([[Lobosa]]) and some green flagellates (e.g., [[Raphidophyte|Raphidophyta]] or ''[[Volvox]]'').
*'''''Open orthomitosis''''' is typical in [[mammals]] and other [[Metazoa]], and in [[land plants]]; but it also occurs in some protists.

===Errors and other variations===
[[File:Atypical mitosis.jpg|thumb|right|200px|An abnormal (tripolar) mitosis (12 o'clock position) in a precancerous lesion of the stomach ([[H&E stain]])]]
Errors can occur during mitosis, especially during early [[embryo]]nic development in humans.<ref>{{cite journal | vauthors = Mantikou E, Wong KM, Repping S, Mastenbroek S | title = Molecular origin of mitotic aneuploidies in preimplantation embryos | journal = Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease | volume = 1822 | issue = 12 | pages = 1921–30 | date = December 2012 | pmid = 22771499 | doi = 10.1016/j.bbadis.2012.06.013 | doi-access = free }}</ref> During each step of mitosis, there are normally checkpoints as well that control the normal outcome of mitosis.<ref>{{cite journal |last1=Wassmann |first1=Katja |last2=Benezra |first2=Robert |title=Mitotic checkpoints: from yeast to cancer |journal=Current Opinion in Genetics & Development |date=February 2001 |volume=11 |issue=1 |pages=83–90 |doi=10.1016/S0959-437X(00)00161-1 |pmid=11163156 }}</ref> But, occasionally to almost rarely, mistakes will happen. Mitotic errors can create [[aneuploidy|aneuploid]] cells that have too few or too many of one or more chromosomes, a condition associated with [[cancer]].<ref name="Draviam-2004"/><ref>{{cite journal | vauthors = Santaguida S, Amon A | title = Short- and long-term effects of chromosome mis-segregation and aneuploidy | journal = Nature Reviews. Molecular Cell Biology | volume = 16 | issue = 8 | pages = 473–85 | date = August 2015 | pmid = 26204159 | doi = 10.1038/nrm4025 | hdl = 1721.1/117201 | hdl-access = free }}</ref>  Early human embryos, cancer cells, infected or intoxicated cells can also suffer from pathological division into three or more daughter cells (tripolar or multipolar mitosis), resulting in severe errors in their chromosomal complements.<ref name="Kalatova-2015"/>

In ''[[nondisjunction]]'', sister chromatids fail to separate during anaphase.<ref name="Iourov-2006">{{cite book | vauthors = Iourov IY, Vorsanova SG, Yurov YB | veditors = Jeon KJ |title=International Review Of Cytology: A Survey of Cell Biology|date=2006|publisher=Academic Press|location=Waltham, MA |isbn=978-0-08-046350-6|page=146|chapter=Chromosomal Variations in Mammalian Neuronal Cells: Known Facts and Attractive Hypotheses |volume=249}}</ref> One daughter cell receives both sister chromatids from the nondisjoining chromosome and the other cell receives none. As a result, the former cell gets three copies of the chromosome, a condition known as ''[[trisomy]]'', and the latter will have only one copy, a condition known as ''[[monosomy]]''. On occasion, when cells experience nondisjunction, they fail to complete cytokinesis and retain both nuclei in one cell, resulting in [[binucleated cells]].<ref>{{cite journal | vauthors = Shi Q, King RW | title = Chromosome nondisjunction yields tetraploid rather than aneuploid cells in human cell lines | journal = Nature | volume = 437 | issue = 7061 | pages = 1038–42 | date = October 2005 | pmid = 16222248 | doi = 10.1038/nature03958 | bibcode = 2005Natur.437.1038S }}</ref>

''[[Anaphase lag]]'' occurs when the movement of one chromatid is impeded during anaphase.<ref name="Iourov-2006"/> This may be caused by a failure of the mitotic spindle to properly attach to the chromosome. The lagging chromatid is excluded from both nuclei and is lost. Therefore, one of the daughter cells will be monosomic for that chromosome.

''[[Endoreduplication]]'' (or endoreplication) occurs when chromosomes duplicate but the cell does not subsequently divide. This results in [[polyploid]] cells or, if the chromosomes duplicates repeatedly, [[polytene chromosomes]].<ref name="Iourov-2006"/><ref name="Edgar-2001">{{cite journal | vauthors = Edgar BA, Orr-Weaver TL | title = Endoreplication cell cycles: more for less | journal = Cell | volume = 105 | issue = 3 | pages = 297–306 | date = May 2001 | pmid = 11348589 | doi = 10.1016/S0092-8674(01)00334-8 | doi-access = free }}</ref> Endoreduplication is found in many species and appears to be a normal part of [[developmental biology|development]].<ref name="Edgar-2001"/> [[Endomitosis]] is a variant of endoreduplication in which cells replicate their chromosomes during S phase and enter, but prematurely terminate, mitosis. Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus.<ref name="Lilly-2005"/><ref name="Lee-2009">{{cite journal | vauthors = Lee HO, Davidson JM, Duronio RJ | title = Endoreplication: polyploidy with purpose | journal = Genes & Development | volume = 23 | issue = 21 | pages = 2461–77 | date = November 2009 | pmid = 19884253 | pmc = 2779750 | doi = 10.1101/gad.1829209 }}</ref> The cells then re-enter G<sub>1</sub> and S phase and replicate their chromosomes again.<ref name="Lee-2009"/> This may occur multiple times, increasing the chromosome number with each round of replication and endomitosis. [[Platelet]]-producing [[megakaryocytes]] go through endomitosis during cell differentiation.<ref name="Italiano-2003"/><ref>{{cite journal | vauthors = Vitrat N, Cohen-Solal K, Pique C, Le Couedic JP, Norol F, Larsen AK, Katz A, Vainchenker W, Debili N | title = Endomitosis of human megakaryocytes are due to abortive mitosis | journal = Blood | volume = 91 | issue = 10 | pages = 3711–23 | date = May 1998 | pmid = 9573008 | doi = 10.1182/blood.V91.10.3711 | doi-access = free }}</ref>

''[[Amitosis]]'' in ciliates and in animal placental tissues results in a random distribution of parental alleles.

''Karyokinesis without cytokinesis'' originates [[multinucleated]] cells  called [[coenocytes]].

==Diagnostic marker==
[[File:Mitosis appearances in breast cancer.jpg|thumb|Mitosis appearances in [[breast cancer]]]]
In [[histopathology]], the mitosis rate (mitotic count or mitotic index) is an important parameter in various types of tissue samples, for diagnosis as well as to further specify the aggressiveness of tumors. For example, there is routinely a quantification of [[Breast cancer classification#Mitotic count|mitotic count in breast cancer classification]].<ref>{{cite web|url=http://surgpathcriteria.stanford.edu/breast/infductcabr/grading.html|title=Infiltrating Ductal Carcinoma of the Breast (Carcinoma of No Special Type)|website=[[Stanford University School of Medicine]]|access-date=2019-10-02|archive-url=https://web.archive.org/web/20190911054536/http://surgpathcriteria.stanford.edu/breast/infductcabr/grading.html|archive-date=2019-09-11|url-status=live}}</ref> The mitoses must be counted in an area of the highest mitotic activity. Visually identifying these areas, is difficult in tumors with very high mitotic activity.<ref>{{cite journal | vauthors = Bertram CA, Aubreville M, Gurtner C, Bartel A, Corner SM, Dettwiler M, Kershaw O, Noland EL, Schmidt A, Sledge DG, Smedley RC, Thaiwong T, Kiupel M, Maier A, Klopfleisch R | display-authors = 6 | title = Computerized Calculation of Mitotic Count Distribution in Canine Cutaneous Mast Cell Tumor Sections: Mitotic Count Is Area Dependent | language = en-US | journal = Veterinary Pathology | volume = 57 | issue = 2 | pages = 214–226 | date = March 2020 | pmid = 31808382 | doi = 10.1177/0300985819890686 | doi-access = free }}</ref> Also, the detection of atypical forms of mitosis can be used both as a diagnostic and prognostic marker.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}} For example, ''lag-type mitosis'' (non-attached condensed [[chromatin]] in the area of the mitotic figure) indicates high risk [[human papillomavirus infection]]-related [[cervical cancer]].{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}} In order to improve the reproducibility and accuracy of the mitotic count, automated image analysis using deep learning-based algorithms have been proposed.<ref>{{cite journal |last1=Bertram |first1=Christof A |last2=Aubreville |first2=Marc |last3=Donovan |first3=Taryn A |last4=Bartel |first4=Alexander |last5=Wilm |first5=Frauke |last6=Marzahl |first6=Christian |last7=Assenmacher |first7=Charles-Antoine |last8=Becker |first8=Kathrin |last9=Bennett |first9=Mark |last10=Corner |first10=Sarah |last11=Cossic |first11=Brieuc |last12=Denk |first12=Daniela |last13=Dettwiler |first13=Martina |last14=Gonzalez |first14=Beatriz Garcia |last15=Gurtner |first15=Corinne |last16=Haverkamp |first16=Ann-Kathrin |last17=Heier |first17=Annabelle |last18=Lehmbecker |first18=Annika |last19=Merz |first19=Sophie |last20=Noland |first20=Erika L |last21=Plog |first21=Stephanie |last22=Schmidt |first22=Anja |last23=Sebastian |first23=Franziska |last24=Sledge |first24=Dodd G |last25=Smedley |first25=Rebecca C |last26=Tecilla |first26=Marco |last27=Thaiwong |first27=Tuddow |last28=Fuchs-Baumgartinger |first28=Andrea |last29=Meuten |first29=Donald J |last30=Breininger |first30=Katharina |last31=Kiupel |first31=Matti |last32=Maier |first32=Andreas |last33=Klopfleisch |first33=Robert |title=Computer-assisted mitotic count using a deep learning–based algorithm improves interobserver reproducibility and accuracy |journal=Veterinary Pathology |year=2021 |volume=59 |issue=2 |pages=211–226 |doi=10.1177/03009858211067478 |pmid=34965805 |pmc=8928234 }}</ref> However, further research is needed before those algorithms can be used to routine diagnostics. 
<gallery mode="packed">
File:Normal versus atypical mitosis.jpg|Normal and atypical forms of mitosis in cancer cells. A, normal mitosis; B, [[chromatin bridge]]; C, multipolar mitosis; D, ring mitosis; E, dispersed mitosis; F, asymmetrical mitosis; G, lag-type mitosis; and H, micronuclei. H&E stain.
</gallery>

==Related cell processes==
===Cell rounding===
[[File:Cell-shape-mitosis.png|thumb|right|250px|Cell shape changes through mitosis for a typical [[animal cell]] cultured on a flat surface. The cell undergoes [[mitotic cell rounding]] during spindle assembly and then divides via [[cytokinesis]]. The [[Cell cortex|actomyosin cortex]] is depicted in red, DNA/chromosomes purple, [[microtubules]] green, and membrane and retraction fibers in black. Rounding also occurs in live tissue, as described in the text.]]
{{main|Mitotic cell rounding}}
In animal tissue, most cells round up to a near-spherical shape during mitosis.<ref name="Sauer-1935" /><ref name="Meyer-2011" /><ref name="Luxenburg-2011" /> In [[epithelia]] and [[epidermis]], an efficient rounding process is correlated with proper [[mitotic spindle]] alignment and subsequent correct positioning of daughter cells.<ref name="Meyer-2011" /><ref name="Luxenburg-2011" /><ref name="Nakajima-2013" /><ref name="Cadart-2014" /> Moreover, researchers have found that if rounding is heavily suppressed it may result in spindle defects, primarily pole splitting and failure to efficiently capture [[chromosomes]].<ref name="Lancaster-2013" /> Therefore, [[mitotic cell rounding]] is thought to play a protective role in ensuring accurate mitosis.<ref name="Cadart-2014" /><ref name="Lancaster-2014" />

Rounding forces are driven by reorganization of [[F-actin]] and [[myosin]] (actomyosin) into a contractile homogeneous [[cell cortex]] that 1) rigidifies the cell periphery<ref name="Lancaster-2014" /><ref name="Maddox-2003" /><ref name="Matthews-2012" /> and 2) facilitates generation of intracellular [[hydrostatic pressure]] (up to 10 fold higher than [[interphase]]).<ref name="Stewart-2011" /><ref name="Fischer-Friedrich-2014" /><ref name="Ramanathan-2015" /> The generation of intracellular pressure is particularly critical under confinement, such as would be important in a tissue scenario, where outward forces must be produced to round up against surrounding cells and/or the [[extracellular matrix]]. Generation of pressure is dependent on [[formin]]-mediated [[F-actin]] nucleation<ref name="Ramanathan-2015" /> and [[Rho kinase]] (ROCK)-mediated [[myosin II]] contraction,<ref name="Maddox-2003" /><ref name="Stewart-2011" /><ref name="Ramanathan-2015" /> both of which are governed upstream by signaling pathways [[RhoA]] and [[ECT2]]<ref name="Maddox-2003" /><ref name="Matthews-2012" /> through the activity of [[Cdk1]].<ref name="Ramanathan-2015" /> Due to its importance in mitosis, the molecular components and dynamics of the mitotic [[Cell cortex|actomyosin cortex]] is an area of active research.

===Mitotic recombination===

Mitotic cells irradiated with [[X-ray]]s in the [[G1 phase]] of the [[cell cycle]] repair recombinogenic [[DNA damage (naturally occurring)|DNA damages]] primarily by [[Homologous recombination|recombination]] between [[homologous chromosome]]s.<ref name="Kadyk-1992">{{cite journal | vauthors = Kadyk LC, Hartwell LH | title = Sister chromatids are preferred over homologs as substrates for recombinational repair in Saccharomyces cerevisiae | journal = Genetics | volume = 132 | issue = 2 | pages = 387–402 | date = October 1992 | doi = 10.1093/genetics/132.2.387 | pmid = 1427035 | pmc = 1205144 }}</ref>   Mitotic cells irradiated in the [[G2 phase]] repair such damages preferentially by [[sister chromatid exchange|sister-chromatid recombination]].<ref name="Kadyk-1992" />  [[Mutation]]s in [[gene]]s encoding enzymes employed in recombination cause cells to have increased sensitivity to being killed by a variety of DNA damaging agents.<ref>{{cite journal | vauthors = Botthof JG, Bielczyk-Maczyńska E, Ferreira L, Cvejic A | title = rad51 leads to Fanconi anemia-like symptoms in zebrafish | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 22 | pages = E4452–E4461 | date = May 2017 | pmid = 28512217 | pmc = 5465903 | doi = 10.1073/pnas.1620631114 | quote = Here we provide in vivo evidence that the decrease in HSPC numbers in adult fish indeed stems from a combination of decreased proliferation and increased apoptosis during embryonic development. This defect appears to be mediated via p53(10), as our p53/rad51 double mutants did not display any observable hematological defects in embryos or adults. | doi-access = free }}</ref><ref>{{cite journal | vauthors = Stürzbecher HW, Donzelmann B, Henning W, Knippschild U, Buchhop S | title = p53 is linked directly to homologous recombination processes via RAD51/RecA protein interaction | journal = The EMBO Journal | volume = 15 | issue = 8 | pages = 1992–2002 | date = April 1996 | pmid = 8617246 | pmc = 450118 | doi = 10.1002/j.1460-2075.1996.tb00550.x }}</ref><ref>{{cite journal | vauthors = Sonoda E, Sasaki MS, Buerstedde JM, Bezzubova O, Shinohara A, Ogawa H, Takata M, Yamaguchi-Iwai Y, Takeda S | display-authors = 6 | title = Rad51-deficient vertebrate cells accumulate chromosomal breaks prior to cell death | journal = The EMBO Journal | volume = 17 | issue = 2 | pages = 598–608 | date = January 1998 | pmid = 9430650 | pmc = 1170409 | doi = 10.1093/emboj/17.2.598 }}</ref> These findings suggest that mitotic recombination is an adaptation for repairing DNA damages including those that are potentially lethal.

== Evolution ==
[[File:Mitosis vs Meiosis Daughter Cells.png|thumb|Mitosis and meiosis differences]]
[[File:Types of mitosis int.svg|thumb|Some types of cell division in prokaryotes and eukaryotes]]

There are prokaryotic [[Homology (biology)|homologs]] of all the key molecules of eukaryotic mitosis (e.g., actins, tubulins). Being a universal eukaryotic property, mitosis probably arose at the base of the eukaryotic tree. As mitosis is less complex than [[meiosis]], meiosis may have arisen after mitosis.<ref name="Wilkins-2009">{{cite journal | vauthors = Wilkins AS, Holliday R | title = The evolution of meiosis from mitosis | journal = Genetics | volume = 181 | issue = 1 | pages = 3–12 | date = January 2009 | pmid = 19139151 | pmc = 2621177 | doi = 10.1534/genetics.108.099762 }}</ref>  However, sexual reproduction involving meiosis is also a primitive characteristic of eukaryotes.<ref>Bernstein, H., Bernstein, C. Evolutionary origin and adaptive function of meiosis. In "Meiosis", Intech Publ (Carol Bernstein and Harris Bernstein editors), Chapter 3: 41–75 (2013).</ref>  Thus meiosis and mitosis may both have evolved, in parallel, from ancestral prokaryotic processes.

While in [[Fission (biology)|bacterial cell division]], after [[DNA replication|duplication of DNA]], two circular chromosomes are attached to a special region of the cell membrane, eukaryotic mitosis is usually characterized by the presence of many linear chromosomes, whose kinetochores attaches to the microtubules of the spindle. In relation to the forms of mitosis, closed intranuclear pleuromitosis seems to be the most primitive type, as it is more similar to bacterial division.<ref name="Raikov-1994"/>

==Gallery==
Mitotic cells can be visualized microscopically by [[staining (biology)|staining]] them with [[fluorescent]] [[antibodies]] and [[dyes]].

{{gallery|width=200|align=center|
File:ProphaseIF.jpg|'''Early prophase''': Polar microtubules, shown as green strands, have established a matrix around the currently intact nucleus, with the condensing chromosomes in blue. The red nodules are the centromeres.|
File:Prometaphase.jpg|'''Early prometaphase''': The nuclear membrane has just disassembled, allowing the microtubules to quickly interact with the kinetochores, which assemble on the centromeres of the condensing chromosomes.|
File:MetaphaseIF.jpg|'''Metaphase''': The centrosomes have moved to the poles of the cell and have established the mitotic spindle. The chromosomes have congressed at the metaphase plate.|
File: Anaphase IF.jpg|'''Anaphase''': Kinetochore microtubules pull the two sets of chromosomes apart, and lengthening polar microtubules push the halves of the dividing cell further apart, while chromosomes are condensed maximally.|
File:TelophaseIF.jpg|'''Telophase''': Reversal of prophase and prometaphase events and thus completing the [[cell cycle]].}}

== See also ==
{{col div|colwidth=30em}}
* [[Chromosome abnormality]]
* [[Cytoskeleton]]
* [[DREAM complex]]
* [[Mitogen]]
* [[Mitosis Promoting Factor]]
* [[Mitotic bookmarking]]

{{colend}}

== References ==
{{Reflist|33em|refs=

<ref name="Albertson-2005">{{cite journal | vauthors = Albertson R, Riggs B, Sullivan W | title = Membrane traffic: a driving force in cytokinesis | journal = Trends in Cell Biology | volume = 15 | issue = 2 | pages = 92–101 | date = February 2005 | pmid = 15695096 | doi = 10.1016/j.tcb.2004.12.008 }}</ref>

<ref name="Blow-2005">{{cite journal | vauthors = Blow JJ, Tanaka TU | title = The chromosome cycle: coordinating replication and segregation. Second in the cycles review series | journal = EMBO Reports | volume = 6 | issue = 11 | pages = 1028–34 | date = November 2005 | pmid = 16264427 | pmc = 1371039 | doi = 10.1038/sj.embor.7400557 }}</ref>

<ref name="Cadart-2014">{{cite journal | vauthors = Cadart C, Zlotek-Zlotkiewicz E, Le Berre M, Piel M, Matthews HK | title = Exploring the function of cell shape and size during mitosis | journal = Developmental Cell | volume = 29 | issue = 2 | pages = 159–69 | date = April 2014 | pmid = 24780736 | doi = 10.1016/j.devcel.2014.04.009 | doi-access = free }}</ref>

<ref name="Chan-2003">{{cite journal | vauthors = Chan GK, Yen TJ | title = The mitotic checkpoint: a signaling pathway that allows a single unattached kinetochore to inhibit mitotic exit | journal = Progress in Cell Cycle Research | volume = 5 | pages = 431–9 | year = 2003 | pmid = 14593737 }}</ref>

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<ref name="Heywood-1978">{{cite journal | vauthors = Heywood P | title = Ultrastructure of mitosis in the chloromonadophycean alga Vacuolaria virescens | journal = Journal of Cell Science | volume = 31 | pages = 37–51 | date = June 1978 | doi = 10.1242/jcs.31.1.37 | pmid = 670329 }}</ref>

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<ref name="Lilly-2005">{{cite journal | vauthors = Lilly MA, Duronio RJ | title = New insights into cell cycle control from the Drosophila endocycle | journal = Oncogene | volume = 24 | issue = 17 | pages = 2765–75 | date = April 2005 | pmid = 15838513 | doi = 10.1038/sj.onc.1208610 | doi-access = free }}</ref>

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<!--<ref name=McConnell1930>{{cite journal | vauthors = McConnell CH | title = The Mitosis Found in Hydra | journal = Science | volume = 72 | issue = 1859 | page = 170 | date = August 1930 | pmid = 17811676 | doi = 10.1126/science.72.1859.170-b }}</ref>-->

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<ref name=Nanninga2001>{{cite journal | vauthors = Nanninga N |title=Cytokinesis in Prokaryotes and Eukaryotes: Common Principles and Different Solutions |journal=[[Microbiology and Molecular Biology Reviews]] |volume=65 |issue=2 |pages=319–33 |year=2001 |pmid=11381104 |pmc=99029 |doi=10.1128/MMBR.65.2.319-333.2001}}</ref>

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<ref name=Zhou2005>{{cite journal | vauthors = Zhou GL, Liu DP, Liang CC | title = Memory mechanisms of active transcription during cell division | journal = BioEssays | volume = 27 | issue = 12 | pages = 1239–45 | date = December 2005 | pmid = 16299763 | doi = 10.1002/bies.20327 }}</ref>
-->

}}

== Further reading ==
{{Refbegin|33em}}
* {{cite book | last = Morgan | first = David L. | name-list-style = vanc |title=The cell cycle: principles of control |publisher=Published by New Science Press in association with Oxford University Press |location=London |year=2007 |isbn=978-0-9539181-2-6 }}
* {{cite book | vauthors = Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P | year = 2002 | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK26934/ | chapter = Mitosis | title = Molecular Biology of the Cell | edition = 4th | publisher = Garland Science | access-date = 2006-01-22 }}
* {{cite book | vauthors = Campbell N, Reece J | date = December 2001 | chapter = The Cell Cycle | title = Biology | edition = 6th | pages = [https://archive.org/details/biologyc00camp/page/217 217–224] | publisher = Benjamin Cummings/Addison-Wesley | location = San Francisco | isbn = 978-0-8053-6624-2 | chapter-url-access = registration | chapter-url = https://archive.org/details/biologyc00camp | url = https://archive.org/details/biologyc00camp/page/217 }}
* {{cite book | vauthors = Cooper G | year = 2000 | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK9958/ | chapter = The Events of M Phase | title = The Cell: A Molecular Approach | edition = 2nd | publisher = Sinaeur Associates, Inc | access-date = 2006-01-22 }}
* {{cite book | vauthors = Freeman S | year = 2002 | chapter = Cell Division | title = Biological Science | url = https://archive.org/details/isbn_9780130911759 | url-access = registration | pages = [https://archive.org/details/isbn_9780130911759/page/155 155–174] | publisher = Prentice Hall | location = Upper Saddle River, NJ | isbn = 978-0-13-081923-9 }}
* {{cite book | vauthors = Lodish H, Berk A, Zipursky L, Matsudaira P, Baltimore D, Darnell J | year = 2000 | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK21466/ | chapter = Overview of the Cell Cycle and Its Control | title = Molecular Cell Biology | edition = 4th | publisher = W. H. Freeman | access-date = 2006-01-22 }}
{{Refend}}

== External links ==
{{Commons category}}
{{Wikiversity|Overview of Cell Biology/Mitosis}}
* [https://www.pbs.org/wgbh/nova/miracle/divide.html# A Flash animation comparing Mitosis and Meiosis]
* [https://web.archive.org/web/20111228073007/http://www.khanacademy.org/video/phases-of-mitosis?playlist=Biology Khan Academy, lecture]
* [http://www.cshprotocols.org/cgi/content/full/2007/3/pdb.prot4674 Studying Mitosis in Cultured Mammalian Cells]
* [http://www.lessonplanet.com/directory_articles/biology_lesson_plans/24_April_2010/361/making_mitosis_movies General K-12 classroom resources for Mitosis]
* [https://archive.today/20120730222759/http://www.semantic-systems-biology.org/apo/ The Cell-Cycle Ontology]
* [http://wormweb.org/celllineage WormWeb.org: Interactive Visualization of the ''C. elegans'' Cell Lineage] – Visualize the entire cell lineage tree and all of the cell divisions of the nematode ''C. elegans''

{{Cell cycle}}
{{Authority control}}

[[Category:Mitosis| ]]
[[Category:Cell cycle]]
[[Category:Articles containing video clips]]
[[Category:1835 in science]]