L>Mitosis and also Meiosis: A Review

Cell Division: A ReviewCells deserve to reproduce one of two people asexually via mitosis or sexually via meiosisIn mitosis, asexual cell division, one diploid (2n) parent cell offers rise to two diploid daughter cell that are genetically the same to the initial cell and also to every other.

You are watching: In what types of organisms does meiosis occur

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Where does mitosis occur?In multicellular organisms, somatic (body) cells undergo mitosis to provide new cells for growth or to change cells that have actually been damaged and also died.Some varieties reproduce via asexually (sometimes called parthenogenesis from the Greek parthen, "virgin" and genesis, "origin". In such species, progenitor cells are developed via mitosis.A clone is a team of geneticallyidentical organisms. Mito - Greek for "thread"(referring to the threadlike appearance of the chromosomes during division)sis - Greek for "theact of"In meiosis, sexual cell division, one diploid (2n) meiocyte (a.k.a. Germline cell) divides to produce four haploid (n) daughter cells. these are additional processed to become sex cells (gametes).meio - "less"Meiosis is "the action of do less"Where does meiosis occur?In sexually reproducing organisms, a meiocyte (a.k.a. Germline cell) experience meiosis to develop gametes. In animals this wake up in the gonads (ovaries in females; testes in males). In plants this wake up in the archegonia in females and in the antheridia in males. In fungi this occurs in dedicated structures ~ above fruiting bodies referred to as sporangia. Protists deserve to undergo meiosis to produce haploid versions of themselves which then can fuse through other people who have done the same thing. Prokaryotes (bacteria and also archaea) don"t experience mitosis or meiosis since they space haploid, and don"t have actually linear chromosomes.
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Mitosis: Asexual cabinet DivisionA cabinet undergoes mitosis to develop two (daughter) cells that are genetically identical to the original (parent) cell.Cellular structures pertinent to mitosis or meiosis: plasma membrane - "gateway" the the cabinet cytosol - proteinaceous matrix containing the organelles mitochondria and also chloroplasts - power transduction organelles save circular DNA separate from the nucleus mitochondrial DNA - mtDNA chloroplasts DNA - cpDNA DNA is circular, not linear resembles bacterial DNA mtDNA, happen on only via maternal parent, is sometimes called "Eve"s DNA" nuclear membrane - dual membrane surrounding the DNA and forming the cell nucleus nucleoplasm - proteinaceous matrix inside the nucleus nucleolus - dark-staining an ar within the cell nucleus locatedat the Nucleolar Organizer an ar (NOR) that the DNA. That is the website of ribosom assembly. centromere - location of the kinetochore,the physical structure to i m sorry spindle yarn attach.
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Chromosomes deserve to be share on the communication of centromere position: metacentric - in ~ the midpoint of the chromosome submetacentric - slightly counter from the midpoint the the chromosome acrocentric - close come the finish of the chromosome telocentric - in ~ the telomere p arm = brief arm that a chromosome q arm = lengthy arm the a chromosomeBy convention, chromosomes are depicted with the quick arms pointing upward.
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Phases that Mitosis

The phases enable us to separate major events of cell division.They are divided somewhat arbitrarily. Yet you need to recognize them, anyway. As soon as a cabinet is not proactively dividing, it may be in interphase - normal state the the cell Gap 1 - proteins needed for cell division are made Synthesis (S) phase - DNA is replicated Gap 2 - short duration between DNA synthetic completion and start of mitosis Prophase euchromatin condenses right into heterochromatin chromosomes are now visible as joined sisters chromatids nuclear source disappears (no an ext ribosome synthesis!) mitotic spindle develops Metaphase spindle microtubules have actually attached come the kinetochores that the sisters chromatids copied chromosomes line up in ~ the metaphase bowl Anaphase spindle traction the sister chromatids apart, drawing them come opposite poles the the cell. Telophase chromosome sets rally at the opposite poles the the cell nuclear envelope forms around each chromosome setelophase is (usually) complied with by cytokinesis, department of the cytoplasm to type two new cells. Each brand-new daughter cell is genetically similar to the parental cell.Meiosis: sex-related Cell DivisionA cell undergoes meiosis to develop four (daughter) cells (gametes) that are genetically different native the original (parent) cell (germline cell).Meiosis produce haploid cells from a diploid cell in ready for sex-related reproduction.Why Sex?The word comes from the Latin secare, which means to cutor division something the was when whole. during meiosis, the do of sex cells, the genetic match of a parental cell is split into two tantamount halves.Meiosis I is reduction division - the cell goes from having two homologous chromosomes every pair to having actually only one member of every homologous pair.Meiosis II is equational division - the cell divides again, in essentially the exact same manner as mitosis: the sister chromatids segregate come two brand-new daughter cells.

Stages of Mitosis: Meiosis I

Prophase IA. leptonema (adjective=leptotene) native the Greeklepto, meaning "thin" 1. Atom envelope and also nucleoli disappear 2. Spindle fibers start to form 3. In animals, centrioles start migration come oppositepoles. 4. Chromosomes start to supercoil 5. "loose" or "rough" pairing that homologs (synapsis is just starting)B. zygonema (adjective = zygotene) from the Greekzygo, an interpretation "yoke" 1. Synaptonemal complex forms: 2 paired homologs space joined by a "ladderlike" complicated of synaptonemal proteins. Once this is complete, the pair is knownas a bivalent. 2. Synapsis is continuing to developC. pachynema (adjective = pachytene) native the Greekpachy, meaning "thick" 1. Chromosomes become much shorter and more thick (moresupercoiling) 2. Sister chromatids begin to unwind, coming to be visibleas 2 chromosomes join at the centromere 3. At this point, the bivalent is recognized as a tetrad4. Crossing end takes place(Note: homologous pairs space analogous come a "husbandand wife", and also the sisters chromatids room analogous come identicaltwins--at least before crossing over.)D. diplonema (adj = diplotene) native the Greek diplo,meaning "double" 1. Synaptonemal complicated starts to disintegrate 2. Chiasmata (crossover points) end up being visible,sometimes as a complex mesh, since there might be many crossover points. 3. Note that sister chromatids room no longer identical,as they have undergone cross over.(Note: some animals stop here, including humans. Meiosis go not proceed until fertilization or ovulation.)E. diakinesis native the Greek dia, meaning"across" and kinesis, an interpretation "movement." 1. Chiasmata relocate tothe tips of the chromatids, wherein they continue to be attached. Thisprocess is well-known as terminalization. 2. Spindle fibers connect to kinetochores. Metaphase I - spindle yarn arrange homologs alongthe metaphase plate in ~ the cell"s equator. Anaphase I- spindle fibers different homologs, carryingthem to opposite poles, but sister chromatids room still connectedat the centromere. In ~ this point, each two-part member the the previous tetrad is well-known as a dyad Telophase I, if it occurs (some species skip this step), is a backwards development to interphase-like conditions. In Meiosis, it is known as interkinesis.Meiosis II: the equational division is physicallythe very same as mitosis, despite the genetic composition in the nuclei space different because of crossing over and recombination.After meiosis, gametogenesis occurs to do the newhaploid cells right into gametes.
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The generalized pet scenario:Male: Testes save on computer 2n spermatogonial cells, whichconstantly renew us via mitosis. At part point, somewill mature and enter right into meiosis come become... primary spermatocytes <2n --> 2(n + n)>. This diploid cells undergo meosis i to end up being two... secondary spermatocytes (n + n). Haploid spermatocytes undergo meiosis II to come to be four spermatids (n). Further spermatogenesis results in the typicalflagellated spermatozoa.Female: Ovaries save on computer 2n oogonial cells, i beg your pardon usually do notrenew themselves. In ~ some allude in your cellular lifespan, these go into into meiosis ns tobecome primary oocytes <2n --> 2(n + n)>, which undergo meosisI. One primary oocyte will come to be a polar body The polar body will divide again to give rise come a second polar body. Meanwhile, the other primary oocyte will become a... secondary oocyte (n + n), which will certainly undergo meiosis IIto come to be one ootid and also another polar body (n).4. Further oogenesis results in the common cytoplasm-richovum.Plant gametogenesis adds an extra generation. Oversimplifying a bit, we have...Male: within the microsporangium the a sporophyte plant, microsporocyte (2n) experience meiosis I and II to develop haploid microspores (n). each microspore grows into a haploid male gametophyte (n) The gametophyte produces sperm (n) via mitosis.Female: within the megasporangium the a sporophyte plant, a megasporocyte (2n) undergoes meiosis I and II to develop asingle haploid megaspore (n) the three polar bodies created degenerate, together in animals The megaspore grows right into the female gametophyte (n), which produces ova (n) via mitosis. polyspermy: combination of more than one sperm through a solitary egg.In animals, this is almost always lethal, as polyploidy (more than two sets of chromosomes) will certainly not create a viable animal embryoIn plants, however, polyspermy is one method that polyploidy can an outcome in speciation.

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Chromosomes: Pairs and Sets

euploidy - the normal number of chromosome to adjust members of every homologous pairs...expected in a given cell (of its species).(from the Greek eu, meaning "true") aneuploidy- much more or fewer than the normal number of chromosomes every homologous pair (from the Greek an - "away" ) nullisomy - a homolgous pair is entirely absent monosomy - just one member of a homologous pair is present trisomy - three duplicates of a homologous chromosome are existing tetrasomy - four copies of a homologous chromosome are existing etc.Aneuploidies can an outcome from nondisjunction - three copies of a homologous chromosome are present- 2 homologs migrate to the same brand-new gamete, leave the other one "blank" lagging chromosome - three copies of a homologous chromosome are present - one member that a homologous pair is not separated right into the newly creating gamete at the same price as the rest, and also is left the end of the nucleus when the nuclear membrane forms.Autosomal aneuploidies are far much more devastating 보다 sex c"some abnormalities; the last are regularly survivable, and also some persons through sex c"some abnormalities have the right to lead completely normal lives and produce regular offspring. ploidy - the variety of complete chromosome to adjust in a cell haploid - one complete collection of chromosomes (in humans, one set comprises 23 chromosomes) diploid - two complete sets that chromosomes (in humans, two sets that 23 chromosomes) triploid - three finish sets the chromosomes tetraploid - three complete sets that chromosomes etc.Because most eukaryotic organisms room diploid, the condition of having much more than two complete sets the chromosomes is known, generically, together polyploidy