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Not to be confused with Meiosis, Miosis, Myiasis, Myositis, or Myosotis. Mitosis_sentence_0

In cell biology, mitosis (/maɪˈtoʊsɪs/) is a part of the cell cycle, in which, replicated chromosomes are separated into two new nuclei. Mitosis_sentence_1

Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. Mitosis_sentence_2

In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA is replicated) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. Mitosis_sentence_3

The different stages of Mitosis all together define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. Mitosis_sentence_4

The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. Mitosis_sentence_5

These stages are prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis_sentence_6

During mitosis, the chromosomes, which have already duplicated, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell. Mitosis_sentence_7

The result is two genetically identical daughter nuclei. Mitosis_sentence_8

The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells. Mitosis_sentence_9

The different phases of mitosis can be visualized in real time, using live cell imaging. Mitosis_sentence_10

Producing three or more daughter cells instead of the normal two is a mitotic error called tripolar mitosis or multipolar mitosis (direct cell triplication / multiplication). Mitosis_sentence_11

Other errors during mitosis can induce apoptosis (programmed cell death) or cause mutations. Mitosis_sentence_12

Certain types of cancer can arise from such mutations. Mitosis_sentence_13

Mitosis occurs only in eukaryotic cells. Mitosis_sentence_14

Prokaryotic cells, which lack a nucleus, divide by a different process called binary fission. Mitosis_sentence_15

Mitosis varies between organisms. Mitosis_sentence_16

For example, animal cells undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, whereas fungi undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus. Mitosis_sentence_17

Most animal cells undergo a shape change, known as mitotic cell rounding, to adopt a near spherical morphology at the start of mitosis. Mitosis_sentence_18

Most human cells are produced by mitotic cell division. Mitosis_sentence_19

Important exceptions include the gametessperm and egg cells – which are produced by meiosis. Mitosis_sentence_20

Discovery Mitosis_section_0

Numerous descriptions of cell division were made during 18th and 19th centuries, with various degrees of accuracy. Mitosis_sentence_21

In 1835, the German botanist Hugo von Mohl, described cell division in the green alga Cladophora glomerata, stating that multiplication of cells occurs through cell division. Mitosis_sentence_22

In 1838, Matthias Jakob Schleiden affirmed that the formation of new cells in their interior was a general law for cell multiplication in plants, a view later rejected in favour of Mohl model, due to contributions of Robert Remak and others. Mitosis_sentence_23

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. Mitosis_sentence_24

Bütschli, Schneider and Fol might have also claimed the discovery of the process presently known as "mitosis". Mitosis_sentence_25

In 1873, the German zoologist Otto Bütschli published data from observations on nematodes. Mitosis_sentence_26

A few years later, he discovered and described mitosis based on those observations. Mitosis_sentence_27

The term "mitosis", coined by Walther Flemming in 1882, is derived from the Greek word μίτος (mitos, "warp thread"). Mitosis_sentence_28

There are some alternative names for the process, e.g., "karyokinesis" (nuclear division), a term introduced by Schleicher in 1878, or "equational division", proposed by August Weismann in 1887. Mitosis_sentence_29

However, the term "mitosis" is also used in a broad sense by some authors to refer to karyokinesis and cytokinesis together. Mitosis_sentence_30

Presently, "equational division" is more commonly used to refer to meiosis II, the part of meiosis most like mitosis . Mitosis_sentence_31

Phases Mitosis_section_1

Main article: Cell cycle Mitosis_sentence_32

Overview Mitosis_section_2

The primary result of mitosis and cytokinesis, is the transfer of a parent cell's genome into two daughter cells. Mitosis_sentence_33

The genome is composed of a number of chromosomes—complexes of tightly coiled DNA that contain genetic information vital for proper cell function . Mitosis_sentence_34

Because each resultant daughter cell should be genetically identical to the parent cell, the parent cell must make a copy of each chromosome before mitosis. Mitosis_sentence_35

This occurs during the S phase of interphase. Mitosis_sentence_36

Chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at the centromere. Mitosis_sentence_37

When mitosis begins, the chromosomes condense and become visible. Mitosis_sentence_38

In some eukaryotes, for example animals, the nuclear envelope, which segregates the DNA from the cytoplasm, disintegrates into small vesicles. Mitosis_sentence_39

The nucleolus, which makes ribosomes in the cell, also disappears. Mitosis_sentence_40

Microtubules project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within the cell. Mitosis_sentence_41

The microtubules then contract to pull the sister chromatids of each chromosome apart. Mitosis_sentence_42

Sister chromatids at this point are called daughter chromosomes. Mitosis_sentence_43

As the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase. Mitosis_sentence_44

A new nuclear envelope forms around the separated daughter chromosomes, which decondense to form interphase nuclei. Mitosis_sentence_45

During mitotic progression, typically after the anaphase onset, the cell may undergo cytokinesis. Mitosis_sentence_46

In animal cells, a cell membrane pinches inward between the two developing nuclei to produce two new cells. Mitosis_sentence_47

In plant cells, a cell plate forms between the two nuclei. Mitosis_sentence_48

Cytokinesis does not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis. Mitosis_sentence_49

Interphase Mitosis_section_3

Main article: Interphase Mitosis_sentence_50

The mitotic phase is a relatively short period of the cell cycle. Mitosis_sentence_51

It alternates with the much longer interphase, where the cell prepares itself for the process of cell division. Mitosis_sentence_52

Interphase is divided into three phases: G1 (first gap), S (synthesis), and G2 (second gap). Mitosis_sentence_53

During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. Mitosis_sentence_54

However, chromosomes are replicated only during the S phase. Mitosis_sentence_55

Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and finally divides (M) before restarting the cycle. Mitosis_sentence_56

All these phases in the cell cycle are highly regulated by cyclins, cyclin-dependent kinases, and other cell cycle proteins. Mitosis_sentence_57

The phases follow one another in strict order and there are "checkpoints" that give the cell cues to proceed from one phase to another. Mitosis_sentence_58

Cells may also temporarily or permanently leave the cell cycle and enter G0 phase to stop dividing. Mitosis_sentence_59

This can occur when cells become overcrowded (density-dependent inhibition) or when they differentiate to carry out specific functions for the organism, as is the case for human heart muscle cells and neurons. Mitosis_sentence_60

Some G0 cells have the ability to re-enter the cell cycle. Mitosis_sentence_61

DNA double-strand breaks can be repaired during interphase by two principal processes. Mitosis_sentence_62

The first process, non-homologous end joining (NHEJ), can join the two broken ends of DNA in the G1, S and G2 phases of interphase. Mitosis_sentence_63

The second process, homologous recombinational repair (HRR), is more accurate than NHEJ in repairing double-strand breaks. Mitosis_sentence_64

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 homologs. Mitosis_sentence_65

Interphase helps prepare the cell for mitotic division. Mitosis_sentence_66

It dictates whether the mitotic cell division will occur. Mitosis_sentence_67

It carefully stops the cell from proceeding whenever the cell's DNA is damaged or has not completed an important phase. Mitosis_sentence_68

The interphase is very important as it will determine if mitosis completes successfully. Mitosis_sentence_69

It will reduce the amount of damaged cells produced and the production of cancerous cells. Mitosis_sentence_70

A miscalculation by the key Interphase proteins could be crucial as the latter could potentially create cancerous cells . Mitosis_sentence_71

Today, more research is being done to understand specifically how the phases stated above occur. Mitosis_sentence_72

Mitosis Mitosis_section_4

Preprophase (plant cells) Mitosis_section_5

Main article: Preprophase Mitosis_sentence_73

In plant cells only, prophase is preceded by a pre-prophase stage. Mitosis_sentence_74

In highly vacuolated plant cells, the nucleus has to migrate into the center of the cell before mitosis can begin. Mitosis_sentence_75

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. Mitosis_sentence_76

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. Mitosis_sentence_77

This band marks the position where the cell will eventually divide. Mitosis_sentence_78

The cells of higher plants (such as the flowering plants) 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. Mitosis_sentence_79

The preprophase band disappears during nuclear envelope breakdown and spindle formation in prometaphase. Mitosis_sentence_80

Prophase Mitosis_section_6

Main article: Prophase Mitosis_sentence_81

During prophase, which occurs after G2 interphase, the cell prepares to divide by tightly condensing its chromosomes and initiating mitotic spindle formation. Mitosis_sentence_82

During interphase, the genetic material in the nucleus consists of loosely packed chromatin. Mitosis_sentence_83

At the onset of prophase, chromatin fibers condense into discrete chromosomes that are typically visible at high magnification through a light microscope. Mitosis_sentence_84

In this stage, chromosomes are long, thin and thread-like. Mitosis_sentence_85

Each chromosome has two chromatids. Mitosis_sentence_86

The two chromatids are joined at the centromere. Mitosis_sentence_87

Gene transcription ceases during prophase and does not resume until late anaphase to early G1 phase. Mitosis_sentence_88

The nucleolus also disappears during early prophase. Mitosis_sentence_89

Close to the nucleus of animal cells are structures called centrosomes, consisting of a pair of centrioles surrounded by a loose collection of proteins. Mitosis_sentence_90

The centrosome is the coordinating center for the cell's microtubules. Mitosis_sentence_91

A cell inherits a single centrosome at cell division, which is duplicated by the cell before a new round of mitosis begins, giving a pair of centrosomes. Mitosis_sentence_92

The two centrosomes polymerize tubulin to help form a microtubule spindle apparatus. Mitosis_sentence_93

Motor proteins then push the centrosomes along these microtubules to opposite sides of the cell. Mitosis_sentence_94

Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle apparatus, since they are absent from plants, and are not absolutely required for animal cell mitosis. Mitosis_sentence_95

Prometaphase Mitosis_section_7

Main article: Prometaphase Mitosis_sentence_96

At the beginning of prometaphase in animal cells, phosphorylation of nuclear lamins causes the nuclear envelope to disintegrate into small membrane vesicles. Mitosis_sentence_97

As this happens, microtubules invade the nuclear space. Mitosis_sentence_98

This is called open mitosis, and it occurs in some multicellular organisms. Mitosis_sentence_99

Fungi and some protists, such as algae or trichomonads, undergo a variation called closed mitosis where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope. Mitosis_sentence_100

In late prometaphase, kinetochore microtubules begin to search for and attach to chromosomal kinetochores. Mitosis_sentence_101

A kinetochore is a proteinaceous microtubule-binding structure that forms on the chromosomal centromere during late prophase. Mitosis_sentence_102

A number of polar microtubules find and interact with corresponding polar microtubules from the opposite centrosome to form the mitotic spindle. Mitosis_sentence_103

Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor. Mitosis_sentence_104

When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. Mitosis_sentence_105

This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids. Mitosis_sentence_106

Metaphase Mitosis_section_8

Main article: Metaphase Mitosis_sentence_107

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. Mitosis_sentence_108

The resulting tension causes the chromosomes to align along the metaphase plate or equatorial plane, an imaginary line that is centrally located between the two centrosomes (at approximately the midline of the cell). Mitosis_sentence_109

To ensure equitable distribution of chromosomes at the end of mitosis, the metaphase checkpoint guarantees that kinetochores are properly attached to the mitotic spindle and that the chromosomes are aligned along the metaphase plate. Mitosis_sentence_110

If the cell successfully passes through the metaphase checkpoint, it proceeds to anaphase. Mitosis_sentence_111

Anaphase Mitosis_section_9

Main article: Anaphase Mitosis_sentence_112

During anaphase A, the cohesins that bind sister chromatids together are cleaved, forming two identical daughter chromosomes. Mitosis_sentence_113

Shortening of the kinetochore microtubules pulls the newly formed daughter chromosomes to opposite ends of the cell. Mitosis_sentence_114

During anaphase B, polar microtubules push against each other, causing the cell to elongate. Mitosis_sentence_115

In late anaphase, chromosomes also reach their overall maximal condensation level, to help chromosome segregation and the re-formation of the nucleus. Mitosis_sentence_116

In most animal cells, anaphase A precedes anaphase B, but some vertebrate egg cells demonstrate the opposite order of events. Mitosis_sentence_117

Telophase Mitosis_section_10

Main article: Telophase Mitosis_sentence_118

Telophase (from the Greek word τελος meaning "end") is a reversal of prophase and prometaphase events. Mitosis_sentence_119

At telophase, the polar microtubules continue to lengthen, elongating the cell even more. Mitosis_sentence_120

If the nuclear envelope has broken down, a new nuclear envelope forms using the membrane vesicles of the parent cell's old nuclear envelope. Mitosis_sentence_121

The new envelope forms around each set of separated daughter chromosomes (though the membrane does not enclose the centrosomes) and the nucleolus reappears. Mitosis_sentence_122

Both sets of chromosomes, now surrounded by new nuclear membrane, begin to "relax" or decondense. Mitosis_sentence_123

Mitosis is complete. Mitosis_sentence_124

Each daughter nucleus has an identical set of chromosomes. Mitosis_sentence_125

Cell division may or may not occur at this time depending on the organism. Mitosis_sentence_126

Cytokinesis Mitosis_section_11

Main article: Cytokinesis Mitosis_sentence_127

Cytokinesis is not a phase of mitosis, but rather a separate process necessary for completing cell division. Mitosis_sentence_128

In animal cells, a cleavage furrow (pinch) containing a contractile ring, develops where the metaphase plate used to be, pinching off the separated nuclei. Mitosis_sentence_129

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. Mitosis_sentence_130

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. Mitosis_sentence_131

The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a phycoplast microtubule array during cytokinesis. Mitosis_sentence_132

Each daughter cell has a complete copy of the genome of its parent cell. Mitosis_sentence_133

The end of cytokinesis marks the end of the M-phase. Mitosis_sentence_134

There are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. Mitosis_sentence_135

The most notable occurrence of this is among the fungi, slime molds, and coenocytic algae, but the phenomenon is found in various other organisms. Mitosis_sentence_136

Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of fruit fly embryonic development. Mitosis_sentence_137

Function Mitosis_section_12

Mitosis's "function" or significance relies on 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_sentence_138

Mitosis occurs in the following circumstances: Mitosis_sentence_139


  • 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.Mitosis_item_0_0
  • Cell replacement: In some parts of the 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, red blood cells have a short lifespan (only about 4 months) and new RBCs are formed by mitosis.Mitosis_item_0_1
  • 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.Mitosis_item_0_2
  • Asexual reproduction: Some organisms produce genetically similar offspring through asexual reproduction. For example, the 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.Mitosis_item_0_3

Variations Mitosis_section_13

Forms of mitosis Mitosis_section_14

The mitosis process in the cells of eukaryotic organisms follow a similar pattern, but with variations in three main details. Mitosis_sentence_140

"Closed" and "open" mitosis can be distinguished on the basis of nuclear envelope remaining intact or breaking down. Mitosis_sentence_141

An intermediate form with partial degradation of the nuclear envelope is called "semiopen" mitosis. Mitosis_sentence_142

With respesct to the symmetry of the spindle apparatus during metaphase, an approximately axially symmetric (centered) shape is called as "orthomitosis", distinguished from the eccentric spindles of "pleuromitosis", in which mitotic apparatus has bilateral symmetry. Mitosis_sentence_143

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). Mitosis_sentence_144


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  • Mitosis_item_1_5
  • Mitosis_item_1_6
  • Mitosis_item_1_7
  • Mitosis_item_1_8
  • Mitosis_item_1_9

Nuclear division takes place only in cells of organisms of the eukaryotic domain, as bacteria and archaea have no nucleus. Mitosis_sentence_145

Bacteria and archaea undergo a different type of division.Within each of the eukaryotic supergroups, mitosis of the open form can be found, as well as closed mitosis, except for Excavata, which show exclusively closed mitosis. Mitosis_sentence_146

Following, the occurrence of the forms of mitosis in eukaryotes: Mitosis_sentence_147


Errors and other variations Mitosis_section_15

Errors can occur during mitosis, especially during early embryonic development in humans. Mitosis_sentence_148

During each step of mitosis, there are normally checkpoints as well that control the normal outcome of mitosis . Mitosis_sentence_149

But, occasionally to almost rarely, mistakes will happen. Mitosis_sentence_150

Mitotic errors can create aneuploid cells that have too few or too many of one or more chromosomes, a condition associated with cancer. Mitosis_sentence_151

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. Mitosis_sentence_152

In nondisjunction, sister chromatids fail to separate during anaphase. Mitosis_sentence_153

One daughter cell receives both sister chromatids from the nondisjoining chromosome and the other cell receives none. Mitosis_sentence_154

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. Mitosis_sentence_155

On occasion, when cells experience nondisjunction, they fail to complete cytokinesis and retain both nuclei in one cell, resulting in binucleated cells. Mitosis_sentence_156

Anaphase lag occurs when the movement of one chromatid is impeded during anaphase. Mitosis_sentence_157

This may be caused by a failure of the mitotic spindle to properly attach to the chromosome. Mitosis_sentence_158

The lagging chromatid is excluded from both nuclei and is lost. Mitosis_sentence_159

Therefore, one of the daughter cells will be monosomic for that chromosome. Mitosis_sentence_160

Endoreduplication (or endoreplication) occurs when chromosomes duplicate but the cell does not subsequently divide. Mitosis_sentence_161

This results in polyploid cells or, if the chromosomes duplicates repeatedly, polytene chromosomes. Mitosis_sentence_162

Endoreduplication is found in many species and appears to be a normal part of development. Mitosis_sentence_163

Endomitosis is a variant of endoreduplication in which cells replicate their chromosomes during S phase and enter, but prematurely terminate, mitosis. Mitosis_sentence_164

Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus. Mitosis_sentence_165

The cells then re-enter G1 and S phase and replicate their chromosomes again. Mitosis_sentence_166

This may occur multiple times, increasing the chromosome number with each round of replication and endomitosis. Mitosis_sentence_167

Platelet-producing megakaryocytes go through endomitosis during cell differentiation. Mitosis_sentence_168

Amitosis in ciliates and in animal placental tissues results in a random distribution of parental alleles. Mitosis_sentence_169

Karyokinesis without cytokinesis originates multinucleated cells called coenocytes. Mitosis_sentence_170

Diagnostic marker Mitosis_section_16

In histopathology, the mitosis rate is an important parameter in various types of tissue samples, for diagnosis as well as to further specify the aggressiveness of tumors. Mitosis_sentence_171

For example, there is routinely a quantification of mitotic count in breast cancer classification. Mitosis_sentence_172

The mitoses must be counted in an area of the highest mitotic activity. Mitosis_sentence_173

Visually identifying these areas, is difficult in tumors with very high mitotic activity. Mitosis_sentence_174

Also, the detection of atypical forms of mitosis can be used both as a diagnostic and prognostic marker. Mitosis_sentence_175

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. Mitosis_sentence_176


  • Mitosis_item_3_16

Related cell processes Mitosis_section_17

Cell rounding Mitosis_section_18

Main article: Mitotic cell rounding Mitosis_sentence_177

In animal tissue, most cells round up to a near-spherical shape during mitosis. Mitosis_sentence_178

In epithelia and epidermis, an efficient rounding process is correlated with proper mitotic spindle alignment and subsequent correct positioning of daughter cells. Mitosis_sentence_179

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. Mitosis_sentence_180

Therefore, mitotic cell rounding is thought to play a protective role in ensuring accurate mitosis. Mitosis_sentence_181

Rounding forces are driven by reorganization of F-actin and myosin (actomyosin) into a contractile homogeneous cell cortex that 1) rigidifies the cell periphery and 2) facilitates generation of intracellular hydrostatic pressure (up to 10 fold higher than interphase). Mitosis_sentence_182

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. Mitosis_sentence_183

Generation of pressure is dependent on formin-mediated F-actin nucleation and Rho kinase (ROCK)-mediated myosin II contraction, both of which are governed upstream by signaling pathways RhoA and ECT2 through the activity of Cdk1. Mitosis_sentence_184

Due to its importance in mitosis, the molecular components and dynamics of the mitotic actomyosin cortex is an area of active research. Mitosis_sentence_185

Mitotic recombination Mitosis_section_19

Mitotic cells irradiated with X-rays in the G1 phase of the cell cycle repair recombinogenic DNA damages primarily by recombination between homologous chromosomes. Mitosis_sentence_186

Mitotic cells irradiated in the G2 phase repair such damages preferentially by sister-chromatid recombination. Mitosis_sentence_187

Mutations in genes encoding enzymes employed in recombination cause cells to have increased sensitivity to being killed by a variety of DNA damaging agents. Mitosis_sentence_188

These findings suggest that mitotic recombination is an adaptation for repairing DNA damages including those that are potentially lethal. Mitosis_sentence_189

Evolution Mitosis_section_20

There are prokaryotic homologs of all the key molecules of eukaryotic mitosis (e.g., actins, tubulins). Mitosis_sentence_190

Being a universal eukaryotic property, mitosis probably arose at the base of the eukaryotic tree. Mitosis_sentence_191

As mitosis is less complex than meiosis, meiosis may have arisen after mitosis. Mitosis_sentence_192

However, sexual reproduction involving meiosis is also a primitive characteristic of eukaryotes. Mitosis_sentence_193

Thus meiosis and mitosis may both have evolved, in parallel, from ancestral prokaryotic processes. Mitosis_sentence_194

While in bacterial cell division, after 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. Mitosis_sentence_195

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. Mitosis_sentence_196

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