Like mitosis, meiosis is a formof eukaryotic bio cell division. However, these two procedures distribute geneticmaterial among the resulting daughter cells in very different ways. Mitosiscreates two the same daughter cells that each contain the very same number ofchromosomes as their parental cell. In contrast, meiosis offers rise come fourunique daughter cells, every of which has half the number of chromosomes as the parentcell. Because meiosis creates cells that room destined to end up being gametes (or reproductive cells), thisreduction in chromosome number is critical — without it, the union the twogametes throughout fertilization would an outcome in offspring with twice the normalnumber the chromosomes!
Apart indigenous this palliation in chromosome number, meiosis different from mitosisin yet another way. Specifics meiosis creates new combinations the geneticmaterial in each of the 4 daughter cells. These new combinations an outcome fromthe exchange the DNA in between paired chromosomes. Together exchange method that thegametes created through meiosis exhibit an amazing selection of hereditary variation.
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Finally, uneven mitosis, meiosis requires two rounds of atom division, notjust one. In spite of this fact, countless of the other events of meiosis are similar tothose that take place in mitosis. Because that example, prior to undergoing meiosis, a cellgoes v an interphase period in which it grows, replicates that is chromosomes,and checks all of its solution to ensure the it is ready to divide. Likemitosis, meiosis additionally has unique stages referred to as prophase, metaphase, anaphase,and telophase. A an essential difference, however, is that throughout meiosis, each of thesephases occurs double — once throughout the first round that division, dubbed meiosisI, and also again throughout the 2nd round of division, called meiosis II.
As previously mentioned, the first round the nuclear department that occurs duringthe development of gametes is dubbed meiosisI. The is additionally known as the reductiondivision due to the fact that it outcomes in cells the have fifty percent the number ofchromosomes as the parental cell. Meiosis I consists of four phases: prophase I,metaphase I, anaphase I, and telophase I.
During prophase I, the chromosomescondense and also become visible inside the nucleus. Because each chromosome wasduplicated during the S phase that developed just before prophase I, each nowconsists of 2 sister chromatids join at the centromere. This plan meansthat every chromosome has actually the shape of one X.
Once this chromosomal condensation has occurred, the members the eachchromosome pair (called homologouschromosomes, since they are similar in size and also contain similar genes),align next to each other. At this point, the 2 chromosomes in each pairbecome tightly associated with each other along their lengths in a processcalled synapsis. Then, if thehomologous chromosomes room tightly paired, the members of each pair tradeadjacent bits that DNA in a procedure called crossingover, additionally known together recombination(Figure 1). This trading of genetic material creates distinctive chromosomes thatcontain new combinations that alleles.
At the end of prophase I, the nuclear membrane finallybegins to break down. Exterior the nucleus, the spindle grows out fromcentrosomes on every side the the cell. Together in mitosis, the microtubules of thespindle space responsible because that moving and arranging the chromosomes duringdivision.
", "182", "http://www.ubraintv-jp.com/ubraintv-jp.com_education", "At the end of metaphase one, homologous chromosomes line up in the facility of the cell. Each chromosome looks choose an elongated X-shaped structure. In the pair of chromosomes in ~ top, the chromosome in ~ left is mainly green, yet the lower an ar of the appropriate chromatid is orange. The chromosome at ideal is greatly orange, yet the lower an ar of the left chromatid is green. A second pair the chromosomes exhibiting the same pattern of coloration on your arms is shown listed below the topmost pair. Mitotic spindles are located at each side of the cell. Each spindle apparatus is written of number of white lines, representing fibers, emanating from two oval-shaped structures, representing centrosomes. The fibers connect the centrosomes to the centromeres of every chromosome. Much shorter fibers additionally emanate native the mitotic spindle however are no attached come chromosomes.")" class="inlineLinks">Figure Detail
At the start of metaphase I, microtubules arise from the spindle and also attach come the kinetochore near the centromere of each chromosome. In particular, microtubules indigenous one next of the spindle attach to among the chromosomes in each homologous pair, if microtubules native the other side that the spindle affix to the other member of every pair. With the help of this microtubules, the chromosome pairs then line up along the equator that the cell, termed the metaphase bowl (Figure 2).
Figure 3:During anaphase I, the homologous chromosomes room pulled towards opposite poles of the cell.
", "182", "http://www.ubraintv-jp.com/ubraintv-jp.com_education", "In the pair that chromosomes in ~ top, the chromosome in ~ left is relocating toward the left-hand mitotic spindle; the chromosome is mostly green, however the lower an ar of the appropriate chromatid is orange. The chromosome at ideal is relocating toward the right-hand mitotic spindle. The chromosome is greatly orange, however the lower region of the left chromatid is green. A second pair the chromosomes exhibiting the exact same pattern that coloration on your arms is shown listed below the topmost pair, mirroring the activities of the chromosomes above.")" class="inlineLinks">Figure Detail
During anaphase I, themicrotubules disassemble and contract; this, in turn, off the homologouschromosomes such that the two chromosomes in every pair space pulled toward oppositeends the the cabinet (Figure 3). This separation way that every of the daughtercells that outcomes from meiosis I will have fifty percent the number of chromosomes ofthe original parent cell after interphase. Also, the sister chromatids in every chromosomestill stay connected. As a result, every chromosome maintains its X-shapedstructure.
Figure 4:Telophase I results in the production of two nonidentical daughter cells, each of i m sorry has fifty percent the number of chromosomes the the initial parent cell.
As the brand-new chromosomes reach the spindle during telophase I, the cytoplasm organizes itself and divides in two. There are now two cells, and also each cabinet contains fifty percent the variety of chromosomes as the parent cell. In addition, the 2 daughter cells room not genetically similar to every other due to the fact that of the recombination that arisen during prophase i (Figure 4).
At this point, the first department of meiosis is complete. The cell now restsfor a bit prior to beginning the second meiotic division. Throughout this period,called interkinesis, thenuclear membrane in each of the 2 cells reforms around the chromosomes. Insome cells, the spindle likewise disintegrates and the chromosomes relax (althoughmost often, the spindle remains intact).It is important to note, however, the no chromosomal duplication occurs during this stage.
During meiosis II, the two cellsonce again bicycle through four phases the division. Meiosis II is sometimesreferred to as an equational divisionbecause the does not minimize chromosome number in the daughter cells — rather, thedaughter cells that an outcome from meiosis II have actually the same variety of chromosomesas the "parent" cells that go into meiosis II. (Remember, this "parent" cellsalready have half the variety of chromosomes the the original parent cell thanksto meiosis I.)
As prophaseII begins, the chromosomes when again condense into tight structures, andthe atom membrane disintegrates. In addition, if the spindle to be disassembledduring interkinesis, it revolutionary at this allude in time.
The occasions of metaphase II are similar to those that mitotic metaphase — in bothprocesses, the chromosomes heat up along the cell"s equatorial plate, alsocalled the metaphase plate, in ready for their eventual separation(Figure 5).
During anaphaseII, microtubules from each spindle affix to each sister chromatid in ~ thekinetochore. The sister chromatids climate separate, and also the microtubules pullthem come opposite poles the the cell. Together in mitosis, every chromatid is nowconsidered a different chromosome (Figure 6). This method that the cells thatresult from meiosis II will have actually the same number of chromosomes together the "parent"cells that gone into meiosis II.
Finally, in telophase II, nuclearmembranes reform around the newly separated chromosomes, i m sorry relax and fadefrom view. As soon as the cytoplasm divides, meiosis is complete. There room nowfour daughter cells — 2 from every of the two cells that gotten in meiosis II —and every daughter cell has fifty percent the normal number of chromosomes (Figure 7).Each additionally contains brand-new mixtures of genes within that chromosomes, thanks torecombination throughout meiosis I.
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Meiosis is important because it ensures the allorganisms created via sexual reproduction save the correct number ofchromosomes. Meiosis additionally produces hereditary variation by means of the process ofrecombination. Later, this sports is increased even further as soon as two gametesunite throughout fertilization, thereby producing offspring with distinct combinationsof DNA. This continuous mixing the parental DNA in sex-related reproduction help fuelthe incredible diversity that life on Earth.