A phenotypic trait , simply trait , or character state is a distinct variant of a phenotypic characteristic of an organism ; it may be either inherited or determined environmentally, but typically occurs as a combination of the two. For example, having eye color is a character of an organism, while blue, brown and hazel versions of eye color are traits . The term trait is generally used in genetics , often to describe phenotypic expression of different combinations of alleles in different individual organisms within a single population , such as the famous purple vs. white flower coloration in Gregor Mendel 's pea plants. By contrast, in systematics , the term character state is employed to describe features that represent fixed diagnostic differences among taxa , such as the absence of tails in great apes , relative to other primate groups.
98-551: Sex is the biological trait that determines whether a sexually reproducing organism produces male or female gametes . During sexual reproduction, a male and a female gamete fuse to form a zygote , which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller, more mobile gametes ( spermatozoa , sperm ) are called male , while organisms that produce larger, non-mobile gametes ( ova , often called egg cells) are called female . An organism that produces both types of gamete
196-447: A spermatozoon (produced in vertebrates within the testes ), is a small cell containing a single long flagellum which propels it. Spermatozoa are extremely reduced cells, lacking many cellular components that would be necessary for embryonic development. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization . Female gametes are egg cells. In vertebrates, they are produced within
294-411: A condition associated with cancer . 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. In nondisjunction , sister chromatids fail to separate during anaphase. One daughter cell receives both sister chromatids from
392-443: A group becomes female; when a dominant female is absent, then her partner changes sex from male to female. In many wrasses the opposite is true: the fish are initially female and become male when they reach a certain size. Sequential hermaphroditism also occurs in plants such as Arisaema triphyllum . Many reptiles , including all crocodiles and most turtles , have temperature-dependent sex determination . In these species,
490-415: A new diploid organism. In a plant species, the diploid organism produces a type of haploid spore by meiosis that is capable of undergoing repeated cell division to produce a multicellular haploid organism. In either case, the gametes may be externally similar ( isogamy ) as in the green alga Ulva or may be different in size and other aspects ( anisogamy ). The size difference is greatest in oogamy ,
588-495: 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
686-506: A particular gene. Blood groups in humans is a classic example. The ABO blood group proteins are important in determining blood type in humans, and this is determined by different alleles of the one locus. Schizotypy is an example of a psychological phenotypic trait found in schizophrenia-spectrum disorders. Studies have shown that gender and age influences the expression of schizotypal traits. For instance, certain schizotypal traits may develop further during adolescence, whereas others stay
784-430: A partner of the opposite sex for mating . Animals which live in the water can mate using external fertilization , where the eggs and sperm are released into and combine within the surrounding water. Most animals that live outside of water, however, use internal fertilization , transferring sperm directly into the female to prevent the gametes from drying up. In most birds, both excretion and reproduction are done through
882-442: A selection of the genetic traits of each parent, is exclusive to eukaryotes . Genetic traits are encoded in the deoxyribonucleic acid (DNA) of chromosomes . The eukaryote cell has a set of paired homologous chromosomes , one from each parent, and this double-chromosome stage is called " diploid ". During sexual reproduction, a diploid organism produces specialized haploid sex cells called gametes via meiosis , each of which has
980-411: A single centrosome at cell division, which is 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 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
1078-419: A single individual and are passed on to successive generations. The biochemistry of the intermediate proteins determines how they interact in the cell. Therefore, biochemistry predicts how different combinations of alleles will produce varying traits. Extended expression patterns seen in diploid organisms include facets of incomplete dominance , codominance , and multiple alleles . Incomplete dominance
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#17328452648241176-417: A single posterior opening, called the cloaca —male and female birds touch cloaca to transfer sperm, a process called "cloacal kissing". In many other terrestrial animals, males use specialized sex organs to assist the transport of sperm—these male sex organs are called intromittent organs . In humans and other mammals, this male organ is known as the penis , which enters the female reproductive tract (called
1274-409: A single set of chromosomes. Meiosis involves a stage of genetic recombination via chromosomal crossover , in which regions of DNA are exchanged between matched pairs of chromosomes, to form new chromosomes, each with a new combination of the genes of the parents. Then the chromosomes are separated into single sets in the gametes. When gametes fuse during fertilization, the resulting zygote has half of
1372-426: 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). 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. Within each of the eukaryotic supergroups , mitosis of
1470-459: 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 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 . Due to its importance in mitosis,
1568-520: A true nucleus, divide by a different process called binary fission . Numerous descriptions of cell division were made during 18th and 19th centuries, with various degrees of accuracy. In 1835, the German botanist Hugo von Mohl , described cell division in the green algae Cladophora glomerata , stating that multiplication of cells occurs through cell division. In 1838, Matthias Jakob Schleiden affirmed that "formation of new cells in their interior
1666-446: A type of anisogamy in which a small, motile gamete combines with a much larger, non-motile gamete. In anisogamic organisms, by convention, the larger gamete (called an ovum , or egg cell) is considered female, while the smaller gamete (called a spermatozoon, or sperm cell) is considered male. An individual that produces large gametes is female, and one that produces small gametes is male. An individual that produces both types of gamete
1764-480: A variation called closed mitosis where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope. In late prometaphase, kinetochore microtubules begin to search for and attach to chromosomal kinetochores . A kinetochore is a proteinaceous microtubule-binding structure that forms on the chromosomal centromere during late prophase. A number of polar microtubules find and interact with corresponding polar microtubules from
1862-511: A variety of DNA damaging agents. These findings suggest that mitotic recombination is an adaptation for repairing DNA damages including those that are potentially lethal. There are prokaryotic 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. However, sexual reproduction involving meiosis
1960-451: Is hermaphrodite . In non-hermaphroditic species, the sex of an individual is determined through one of several biological sex-determination systems . Most mammalian species have the XY sex-determination system , where the male usually carries an X and a Y chromosome (XY), and the female usually carries two X chromosomes (XX). Other chromosomal sex-determination systems in animals include
2058-432: Is a hermaphrodite . In some species, a hermaphrodite can self-fertilize and produce an offspring on its own. Most sexually reproducing animals spend their lives as diploid, with the haploid stage reduced to single-cell gametes. The gametes of animals have male and female forms— spermatozoa and egg cells, respectively. These gametes combine to form embryos which develop into new organisms. The male gamete,
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#17328452648242156-422: Is absent. About 99% of vertebrates are gonochoric, and the remaining 1% that are hermaphroditic are almost all fishes. The majority of plants are bisexual , either hermaphrodite (with both stamens and pistil in the same flower) or monoecious . In dioecious species male and female sexes are on separate plants. About 5% of flowering plants are dioecious, resulting from as many as 5000 independent origins. Dioecy
2254-415: Is also a primitive characteristic of eukaryotes. Thus meiosis and mitosis may both have evolved, in parallel, from ancestral prokaryotic processes. 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
2352-566: Is also the first step towards sexual dimorphism and influenced the evolution of various sex differences. It is unclear whether anisogamy first led to the evolution of hermaphroditism or the evolution of gonochorism , and the evolution of sperm and eggs has left no fossil evidence. A 1.2 billion year old fossil from Bangiomorpha pubescens has provided the oldest fossil record for the differentiation of male and female reproductive types and shown that sexes evolved early in eukaryotes. Studies on green algae have provided genetic evidence for
2450-405: Is an obvious, observable, and measurable characteristic of an organism; it is the expression of genes in an observable way. An example of a phenotypic trait is a specific hair color or eye color. Underlying genes, that make up the genotype , determine the hair color, but the hair color observed is the phenotype. The phenotype is dependent on the genetic make-up of the organism, and also influenced by
2548-530: Is called sex determination . The cause may be genetic, environmental, haplodiploidy , or multiple factors. Within animals and other organisms that have genetic sex-determination systems, the determining factor may be the presence of a sex chromosome . In plants that are sexually dimorphic, such as Ginkgo biloba , the liverwort Marchantia polymorpha or the dioecious species in the flowering plant genus Silene , sex may also be determined by sex chromosomes. Non-genetic systems may use environmental cues, such as
2646-714: Is carried by wind to neighboring plants. Some flowering plants have heavier, sticky pollen that is specialized for transportation by insects or larger animals such as hummingbirds and bats , which may be attracted to flowers containing rewards of nectar and pollen. These animals transport the pollen as they move to other flowers, which also contain female reproductive organs, resulting in pollination . Most species of fungus can reproduce sexually and have life cycles with both haploid and diploid phases. These species of fungus are typically isogamous , i.e. lacking male and female specialization. One haploid fungus grows into contact with another, and then they fuse their cells. In some cases,
2744-419: Is common in gymnosperms , in which about 65% of species are dioecious, but most conifers are monoecious. It is generally accepted that isogamy was ancestral to anisogamy and that anisogamy evolved several times independently in different groups of eukaryotes, including protists, algae, plants, and animals. The evolution of anisogamy is synonymous with the origin of male and the origin of female . It
2842-624: Is found in most arachnids , insects such as silverfish ( Apterygota ), dragonflies ( Paleoptera ) and grasshoppers ( Exopterygota ), and some nematodes, crustaceans, and gastropods. In field crickets , for example, insects with a single X chromosome develop as male, while those with two develop as female. In the nematode Caenorhabditis elegans , most worms are self-fertilizing hermaphrodites with an XX karyotype, but occasional abnormalities in chromosome inheritance can give rise to individuals with only one X chromosome—these XO individuals are fertile males (and half their offspring are male). In
2940-592: Is male. In this case, ZZ individuals are male and ZW are female. It is the female gamete that determines the sex of the offspring. This system is used by birds, some fish, and some crustaceans . The majority of butterflies and moths also have a ZW sex-determination system. Females can have Z, ZZW, and even ZZWW. In the XO sex-determination system , males have one X chromosome (XO) while females have two (XX). All other chromosomes in these diploid organisms are paired, but organisms may inherit one or two X chromosomes. This system
3038-412: 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 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
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3136-545: Is needed before those algorithms can be used to routine diagnostics. In animal tissue, most cells round up to a near-spherical shape during mitosis. In epithelia and epidermis , an efficient rounding process is correlated with proper mitotic spindle alignment and subsequent correct positioning of daughter cells. 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 . Therefore, mitotic cell rounding
3234-479: Is preceded by a preprophase stage. In highly 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
3332-408: Is preceded by the S phase of interphase (during which DNA replication occurs) and is followed by telophase and cytokinesis , which divide the cytoplasm , organelles , and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis altogether define the mitotic phase (M phase) of a cell cycle—the division of
3430-453: Is the condition in which neither allele dominates the other in one heterozygote. Instead the phenotype is intermediate in heterozygotes. Thus you can tell that each allele is present in the heterozygote. Codominance refers to the allelic relationship that occurs when two alleles are both expressed in the heterozygote, and both phenotypes are seen simultaneously. Multiple alleles refers to the situation when there are more than 2 common alleles of
3528-399: 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: 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
3626-419: Is the number of X chromosomes that determines sex rather than the presence of a Y chromosome. In the fruit fly individuals with XY are male and individuals with XX are female; however, individuals with XXY or XXX can also be female, and individuals with X can be males. In birds, which have a ZW sex-determination system , the W chromosome carries factors responsible for female development, and default development
3724-540: 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 genetic information vital for proper cell function. 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. This occurs during the S phase of interphase. Chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at
3822-470: Is thought to play a protective role in ensuring accurate mitosis. 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 ). The generation of intracellular pressure is particularly critical under confinement, such as would be important in
3920-407: Is used by some insect species to inseminate females through a wound in the abdominal cavity—a process detrimental to the female's health. Like animals, land plants have specialized male and female gametes. In seed plants , male gametes are produced by reduced male gametophytes that are contained within pollen which have hard coats that protect the male gamete forming cells during transport from
4018-472: 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. Microtubules project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within
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4116-423: The Y chromosome carries factors responsible for triggering male development, making XY sex determination mostly based on the presence or absence of the Y chromosome . It is the male gamete that determines the sex of the offspring. In this system XX mammals typically are female and XY typically are male. However, individuals with XXY or XYY are males, while individuals with X and XXX are females. Unusually,
4214-555: The ZO sex-determination system , males have two Z chromosomes whereas females have one. This system is found in several species of moths. For many species, sex is not determined by inherited traits, but instead by environmental factors such as temperature experienced during development or later in life. In the fern Ceratopteris and other homosporous fern species, the default sex is hermaphrodite, but individuals which grow in soil that has previously supported hermaphrodites are influenced by
4312-584: The ZW system in birds, and the XO system in some insects. Various environmental systems include temperature-dependent sex determination in reptiles and crustaceans. The male and female of a species may be physically alike (sexual monomorphism) or have physical differences ( sexual dimorphism ). In sexually dimorphic species, including most birds and mammals, the sex of an individual is usually identified through observation of that individual's sexual characteristics . Sexual selection or mate choice can accelerate
4410-399: The anthers to the stigma . The female gametes of seed plants are contained within ovules . Once fertilized, these form seeds which, like eggs, contain the nutrients necessary for the initial development of the embryonic plant. The flowers of flowering plants contain their sexual organs. Most flowering plants are hermaphroditic, with both male and female parts in the same flower or on
4508-444: The cohesins that bind sister chromatids together are cleaved, forming two identical daughter chromosomes. 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. In late anaphase, chromosomes also reach their overall maximal condensation level, to help chromosome segregation and
4606-520: The evolutionary link between sexes and mating types . The original form of sex was external fertilization . Internal fertilization , or sex as we know it, evolved later and became dominant for vertebrates after their emergence on land . The most basic role of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. The two most fundamental aspects of sexual reproduction , meiotic recombination and outcrossing , are likely maintained respectively by
4704-400: The ovaries . They are large, immobile cells that contain the nutrients and cellular components necessary for a developing embryo. Egg cells are often associated with other cells which support the development of the embryo, forming an egg . In mammals, the fertilized embryo instead develops within the female, receiving nutrition directly from its mother. Animals are usually mobile and seek out
4802-418: The pheromone antheridiogen to develop as male. The bonelliidae larvae can only develop as males when they encounter a female. Some species can change sex over the course of their lifespan, a phenomenon called sequential hermaphroditism . Teleost fishes are the only vertebrate lineage where sequential hermaphroditism occurs. In clownfish , smaller fish are male, and the dominant and largest fish in
4900-412: The platypus , a monotreme mammal, has ten sex chromosomes; females have ten X chromosomes, and males have five X chromosomes and five Y chromosomes. Platypus egg cells all have five X chromosomes, whereas sperm cells can either have five X chromosomes or five Y chromosomes. XY sex determination is found in other organisms, including insects like the common fruit fly , and some plants. In some cases, it
4998-417: The temperature during early development in crocodiles , to determine the sex of the offspring. Sex determination is often distinct from sex differentiation . Sex determination is the designation for the development stage towards either male or female while sex differentiation is the pathway towards the development of the phenotype . Humans and most other mammals have an XY sex-determination system :
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#17328452648245096-450: The vagina ) to achieve insemination —a process called sexual intercourse . The penis contains a tube through which semen (a fluid containing sperm) travels. In female mammals, the vagina connects with the uterus , an organ which directly supports the development of a fertilized embryo within (a process called gestation ). Because of their motility, animal sexual behavior can involve coercive sex. Traumatic insemination , for example,
5194-399: The adaptive advantages of recombinational repair of genomic DNA damage and genetic complementation which masks the expression of deleterious recessive mutations . Genetic variation , often produced as a byproduct of these processes, may provide long-term advantages in those sexual lineages that favor outcrossing . The biological cause of an organism developing into one sex or the other
5292-418: The anaphase onset, the cell may undergo cytokinesis. In animal cells , a cell membrane pinches inward between the two developing nuclei to produce two new cells. In plant cells , a cell plate forms between the two nuclei. Cytokinesis does not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis. The interphase is a much longer phase of the cell cycle than
5390-440: 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,
5488-418: The carpel, where it delivers male gamete nuclei to fertilize an ovule that eventually develops into a seed. Some hermaphroditic plants are self-fertile, but plants have evolved multiple different self-incompatibility mechanisms to avoid self-fertilization, involving sequential hermaphroditism , molecular recognition systems and morphological mechanisms such as heterostyly . In pines and other conifers ,
5586-406: The carpels are ovules which develop into seeds after fertilization. The male parts of the flower are the stamens : these consist of long filaments arranged between the pistil and the petals that produce pollen in anthers at their tips. When a pollen grain lands upon the stigma on top of a carpel's style, it germinates to produce a pollen tube that grows down through the tissues of the style into
5684-421: The cause of non-viable embryos that fail to implant . Other errors during mitosis can induce mitotic catastrophe , apoptosis (programmed cell death) or cause mutations . Certain types of cancers can arise from such mutations. Mitosis occurs only in eukaryotic cells and varies between organisms. For example, animal cells generally undergo an open mitosis, where the nuclear envelope breaks down before
5782-488: 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
5880-400: 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. In plant cells only, prophase
5978-455: The cell. 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. The different phases of mitosis can be visualized in real time, using live cell imaging . 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
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#17328452648246076-467: The cell. The microtubules then contract to pull the sister chromatids of each chromosome apart. 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
6174-435: The centromere. Gene transcription ceases during prophase and does not resume until late anaphase to early G 1 phase. The nucleolus also disappears during early prophase. Close to the nucleus of an animal cell are structures called centrosomes , consisting of a pair of centrioles surrounded by a loose collection of proteins . The centrosome is the coordinating center for the cell's microtubules . A cell inherits
6272-413: The chromosomes duplicates repeatedly, polytene chromosomes . Endoreduplication is found in many species and appears to be a normal part of development . 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
6370-487: The chromosomes separate, whereas fungal cells generally undergo a closed mitosis, where chromosomes divide within an intact cell nucleus. 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 gametes – sperm and egg cells – which are produced by meiosis . Prokaryotes , bacteria and archaea which lack
6468-545: The cycle. 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 checkpoints that give the cell cues to proceed or not, from one phase to another. Cells may also temporarily or permanently leave the cell cycle and enter G 0 phase to stop dividing. This can occur when cells become overcrowded ( density-dependent inhibition ) or when they differentiate to carry out specific functions for
6566-467: The detection of atypical forms of mitosis can be used both as a diagnostic and prognostic marker. 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 . In order to improve the reproducibility and accuracy of the mitotic count, automated image analysis using deep learning-based algorithms have been proposed. However, further research
6664-453: The discovery of the process presently known as "mitosis". In 1873, the German zoologist Otto Bütschli published data from observations on nematodes . A few years later, he discovered and described mitosis based on those observations. The term "mitosis", coined by Walther Flemming in 1882, is derived from the Greek word μίτος ( mitos , "warp thread"). There are some alternative names for
6762-521: 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 fungi , slime molds , 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 fruit fly embryonic development. The function or significance of mitosis,
6860-795: The environmental conditions to that of the organism is subjected across its ontogenetic development, including various epigenetic processes. Regardless of the degree of influence of genotype versus environment, the phenotype encompasses all of the characteristics of an organism, including traits at multiple levels of biological organization , ranging from behavior and evolutionary history of life traits (e.g., litter size), through morphology (e.g., body height and composition), physiology (e.g., blood pressure), cellular characteristics (e.g., membrane lipid composition, mitochondrial densities), components of biochemical pathways, and even messenger RNA . Different phenotypic traits are caused by different forms of genes , or alleles , which arise by mutation in
6958-509: The evolution of differences between the sexes. The terms male and female typically do not apply in sexually undifferentiated species in which the individuals are isomorphic (look the same) and the gametes are isogamous (indistinguishable in size and shape), such as the green alga Ulva lactuca . Some kinds of functional differences between individuals, such as in fungi , may be referred to as mating types . Sexual reproduction, in which two individuals produce an offspring that possesses
7056-503: The formation of the spindle apparatus, since they are absent from plants, and are not absolutely required for animal cell mitosis. At the beginning of prometaphase in animal cells, phosphorylation of nuclear lamins causes the nuclear envelope to disintegrate into small membrane vesicles . As this happens, microtubules invade the nuclear space. This is called open mitosis , and it occurs in some multicellular organisms. Fungi and some protists , such as algae or trichomonads , undergo
7154-601: The fusion is asymmetric, and the cell which donates only a nucleus (and no accompanying cellular material) could arguably be considered male. Fungi may also have more complex allelic mating systems, with other sexes not accurately described as male, female, or hermaphroditic. Some fungi, including baker's yeast , have mating types that determine compatibility. Yeasts with the same mating types will not fuse with each other to form diploid cells, only with yeast carrying another mating type. Many species of higher fungi produce mushrooms as part of their sexual reproduction . Within
7252-430: The genetic material of the mother and half of the father. The combination of chromosomal crossover and fertilization , bringing the two single sets of chromosomes together to make a new diploid zygote , results in a new organism that contains a different set of the genetic traits of each parent. In animals , the haploid stage only occurs in the gametes, the sex cells that fuse to form a zygote that develops directly into
7350-429: The middle of the cell. 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. Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks
7448-456: 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 mitotic count in breast cancer classification . 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. Also,
7546-616: The molecular components and dynamics of the mitotic actomyosin cortex is an area of active research. Mitotic cells irradiated with X-rays in the G1 phase of the cell cycle repair recombinogenic DNA damages primarily by recombination between homologous chromosomes . Mitotic cells irradiated in the G2 phase repair such damages preferentially by sister-chromatid recombination . Mutations in genes encoding enzymes employed in recombination cause cells to have increased sensitivity to being killed by
7644-519: The mother cell into two daughter cells genetically identical to each other. 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 fibers that pull one copy of each chromosome to opposite sides of
7742-454: The movement of one chromatid is impeded during anaphase. 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
7840-453: The mushroom, diploid cells are formed, later dividing into haploid spores . A sexual system is a distribution of male and female functions across organisms in a species. Approximately 95% of animal species have separate male and female individuals, and are said to be gonochoric . About 5% of animal species are hermaphroditic. This low percentage is partially attributable to the very large number of insect species, in which hermaphroditism
7938-424: 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 . Anaphase lag occurs when
8036-564: The open form can be found, as well as closed mitosis, except for unicellular Excavata , which show exclusively closed mitosis. Following, the occurrence of the forms of mitosis in eukaryotes: Errors can occur during mitosis, especially during early embryonic development in humans. During each step of mitosis, there are normally checkpoints as well that control the normal outcome of mitosis. But, occasionally to almost rarely, mistakes will happen. Mitotic errors can create aneuploid cells that have too few or too many of one or more chromosomes,
8134-438: The opposite centrosome to form the mitotic spindle. Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor . When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides
8232-434: The organism, as is the case for human heart muscle cells and neurons . Some G 0 cells have the ability to re-enter the cell cycle. DNA double-strand breaks can be repaired during interphase by two principal processes. 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. The second process, homologous recombinational repair (HRR),
8330-476: The organism. 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. In both animal and plant cells, cell division is also driven by vesicles derived from the Golgi apparatus , which move along microtubules to
8428-539: The original nucleus. The cells then re-enter G 1 and S phase and replicate their chromosomes again. 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. Amitosis in ciliates and in animal placental tissues results in a random distribution of parental alleles. Karyokinesis without cytokinesis originates multinucleated cells called coenocytes . In histopathology ,
8526-568: The plasma membrane around the equatorial plane of the future mitotic spindle . This band marks the position where the cell will eventually divide. 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. The preprophase band disappears during nuclear envelope breakdown and spindle formation in prometaphase. During prophase, which occurs after G 2 interphase,
8624-458: The process, e.g., "karyokinesis" (nuclear division), a term introduced by Schleicher in 1878, or "equational division", proposed by August Weismann in 1887. However, the term "mitosis" is also used in a broad sense by some authors to refer to karyokinesis and cytokinesis together. Presently, "equational division" is more commonly used to refer to meiosis II , the part of meiosis most like mitosis. The primary result of mitosis and cytokinesis
8722-411: The pulling force necessary to later separate the chromosome's two chromatids. 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
8820-400: The re-formation of the nucleus. In most animal cells, anaphase A precedes anaphase B, but some vertebrate egg cells demonstrate the opposite order of events. Telophase (from the 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,
8918-555: The relatively short M phase. During interphase the cell prepares itself for the process of cell division. Interphase is divided into three subphases: G 1 (first gap) , S (synthesis) , and G 2 (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 1 ), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G 2 ), and finally divides (M) before restarting
9016-409: The same during this period. Mitosis This is an accepted version of this page Mitosis ( / m aɪ ˈ t oʊ s ɪ s / ) is a part of the cell cycle in which replicated chromosomes are separated into two new 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. Mitosis
9114-403: The same plant in single sex flowers, about 5% of plant species have individual plants that are one sex or the other. The female parts, in the center of a hermaphroditic or female flower, are the pistils , each unit consisting of a carpel , a style and a stigma . Two or more of these reproductive units may be merged to form a single compound pistil , the fused carpels forming an ovary . Within
9212-676: The sex of offspring is determined by fertilization ( arrhenotoky or pseudo-arrhenotoky resulting in males) rather than the assortment of chromosomes during meiosis. A sex ratio is the ratio of males to females in a population . As explained by Fisher's principle , for evolutionary reasons this is typically about 1:1 in species which reproduce sexually . However, many species deviate from an even sex ratio, either periodically or permanently. Examples include parthenogenic and androgenetic species, periodically mating organisms such as aphids, some eusocial wasps , bees , ants , and termites . Biological trait A phenotypic trait
9310-524: The sex organs are produced within cones that have male and female forms. Male cones are smaller than female ones and produce pollen, which is transported by wind to land in female cones. The larger and longer-lived female cones are typically more durable, and contain ovules within them that develop into seeds after fertilization. Because seed plants are immobile, they depend upon passive methods for transporting pollen grains to other plants. Many, including conifers and grasses, produce lightweight pollen which
9408-621: The temperature experienced by the embryos during their development determines their sex. In some turtles, for example, males are produced at lower temperatures than females; but Macroclemys females are produced at temperatures lower than 22 °C or above 28 °C, while males are produced in between those temperatures. Certain insects, such as honey bees and ants , use a haplodiploid sex-determination system . Diploid bees and ants are generally female, and haploid individuals (which develop from unfertilized eggs) are male. This sex-determination system results in highly biased sex ratios , as
9506-417: The two centrosomes (at approximately the midline of the cell). 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. If the cell successfully passes through the metaphase checkpoint, it proceeds to anaphase. During anaphase A ,
9604-455: 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. 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. Bütschli, Schneider and Fol might have also claimed
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