Meiosis is a specialized form of nuclear division in which there two successive nuclear divisions (meiosis I and II) without any chromosome replication between them. Each division can be divided into 4 phases similar to those of mitosis (pro-, meta-, ana- and telophase). Meiosis occurs during the formation of gametes in animals Feb 11, · Meiosis is broken up into into two parts: meiosis I and meiosis II which both consist of four parts. Meiosis I occurs first after DNA replication and consists of prophase I, metaphase I, anaphase I, and telophase I. Prophase I, much like prophase in mitosis, is when the chromosomes shorten and the mitotic spindle forms Words | 3 Pages. Mitosis Meiosis Most of the times people get injuries, complex or simple one like bruises and, within a period of time, these injuries heal. This healing process is made possible by cell division whereby a single cell divides to form two and the process continues. The same process also helps living things grow, for example, over 2 trillion cells divide every day in human beings
Meiosis - College Essay Examples
Essay on the Introduction to Meiosis: Meiosis is a type of cell division that occurs only in eukaryotes, produces haploid n sex cells or gametes which contain a single copy of each chromosome from diploid 2n cells which contain two copies of each chromosome. In this process one DNA replication followed by two successive nuclear and cellular divisions Meiosis I and Meiosis II. As in mitosis, meiosis is preceded by a process of DNA replication that converts each chromosome into two sister chromatids Fig.
The resulting four gametes are haploid, meaning that they contain half the number of chromosomes. This is the reason as to why meiosis cell division is also referred to as reduction division. During fertilization, two gametes, one from the mother and another from the father, fuse, thus resulting in doubling of chromosome number.
The fusion of gametes leads to the meiosis essay of a zygote that has the same chromosome number of the parents. Variation occurs in the resulting zygote due to the process of meiosis and fertilization of gametes.
Zygote after attaining maturity is capable of dividing into daughter cells. There are two meiosis essay sex cells meiosis essay gametes- sperm meiosis essay eggs. Males produce sperm which females produce meiosis essay because they are produced from germ cells, gametes are likewise haploid.
In order to create a new meiosis essay via sexual reproduction, a sperm cell needs to activate an egg by joining it in a fertilization process, meiosis essay. These two haploid cells can unite in to a diploid cell, which can then develop into a new individual, meiosis essay. The sexual reproductive processes ensure the resulting offspring will have an equal maternal and paternal genetic contribution, meiosis essay. Life cycles of all sexually-reproducing organisms follow this meiosis essay of alternation of generations, meiosis essay.
The 2n adult produces 1n gametes by the process of meiosis. These unite in the process of syngamy to produce a new 1n generation. Thus, the life cycles alternate between 1n and 2n stages, and between the processes of meiosis and syngamy. Meiosis was discovered and described for the first time in sea urchin eggs inby a German biologist Oscar Hertwig In animals meiosis helps in the production of the gametes: sperni and eggs, while in plants used to produce spores. The process of meiosis is exhibited by higher forms of organisms, which reproduce sexually.
In plants, meiosis essay, meiosis meiosis essay observed after meiosis essay. production; whereas, in animals, meiosis takes place during gamete sperm and egg formation.
Like other cell division, meiosis produces daughter cells. However, there is a significant difference between meiosis and other types of cell division like mitosis or binary fission. In meiosis, meiosis essay, the parent cell divides and produces four gametes that are not capable of further division; whereas, in other types of cell division, the parent cell produces identical daughter cells, which can undergo division on their own.
Essay on the Process of Meiosis: The steps in meiosis are similar to mitosis and even known by having the same names. However, there is a significant difference in regions to the way the chromosomes line up initially. In mitosis, chromosomes line up individually, while in meiosis, the two chromosomes in each homologous pair line up next to each other as pairs, meiosis essay.
This pairing process is called synapsis, and the resulting homologous pair is called a bivalent in reference to the two chromosomes or a tetrad in reference to the four sister chromatids involved. There are two stages of meiosis, namely, meiosis I and meiosis II. The parent cell or the dividing cell undergoes a preparatory phase, meiosis essay, known as interphase, before entering the two stages of meiosis.
In the interphase, the parent cell synthesizes more DNA deoxyribonucleic acid and proteins, increasing the overall size and mass of the cell. As a part of the preparatory phase, the dividing cell duplicates or doubles its chromosomes. With these major changes, the parent cell enters the first stage of meiosis. Prior to meiosis, all chromosomes are duplicated in a process similar to chromosomes duplication prior to mitosis.
Outside the nucleus of animal cells there are two centrosomes, each containing a pair of centrioles. The two centrosomes are produced by the duplication of a single centrosome during premeiotic interphase. The centrosomes serve as microtubule organizing centers MTOCs, meiosis essay. Microtubules extend radially from centrosomes, meiosis essay, forming an aster. PI ant cells do not have centrosomes.
Essay on the Divisions of Meiosis: i. First Division of Meiosis Meiosis I :. In beginning of prophase I, meiosis essay, the chromosomes have already duplicated, and they coil and become shorter and thicker and visible under the light microscope Fig. The duplicated homologous chromosomes pair, and crossing-over meiosis essay physical exchange of chromosome parts occurs. Crossing-over is the process that can give rise to genetic recombination. At this point, each homologous chromosome pair is visible as a bivalent tetrada tight grouping of two chromosomes, each consisting of two sister chromatids.
The sites of crossing-over are seen as crisscrossed non-sister chromatids and are called chiasmata singular: chiasma. The homologous meiosis essay pair and exchange DNA, to form recombinant chromosomes. Chromosomes start to condense, meiosis essay. Homologous dyads pairs of sister chromatids find each other and align themselves from end to end with the aid of an axial element that contains cohesins.
In budding yeast and perhaps other eukaryotes the process follows a period of trial-and-error. Any meiosis essay dyads pair at their centromeres. If they meiosis essay not homologs, they separate and try again. Double-stranded breaks DSBs often occur in the DNA of the chromatids, and these may be necessary for the homologs to recognize each other. Homologous chromosomes become closely associated synapsis to form pairs meiosis essay chromosomes bivalents consisting of four chromatids tetrads.
The pairing of homologous chromosomes is known as synapsis Gr. The synapsis begins at one or more points along meiosis essay length of the homologues chromosomes. Three types of synapsis have been observed preterminal, meiosis essay, precentric and localized on the basis of position of synapsis. The paired homologous chromosomes are joined by a roughly 0.
Synaptonemal complex helps stabilize the pairing of homologous chromosomes and to facilitate the cytogenetical activity called crossing over or recombination. Crossing over takes place between pairs of homologous chromosomes to form chiasmata sing, meiosis essay. They are named for the idea that they represent points where DNA recombination is occurring. There must be at least one for each bivalent if meiosis essay is to succeed, meiosis essay.
There is often more, each one presumably representing the point of a crossover. They contain enzymes known to be needed for DNA recombination and repair. The steps in recombining DNA continue to the end of pachytene. Homologous chromosomes meiosis essay to separate but remain attached by chiasmata. DNA recombination is complete.
The synaptonemal complex begins to break down. The chromatids meiosis essay to pull apart revealing chiasmata. At first the chiasmata are located at the sites of the recombination nodules, but later they migrate towards the ends of the chromatids.
Homologous chromosomes continue to separate, meiosis essay, and chiasmata move to the ends of the chromosomes. In some organisms, the chromosomes decondense and begin to be transcribed for a time. This is followed by the chromosomes recondensing in preparation for metaphase I, meiosis essay.
In creatures where this does not occur, meiosis essay, the chromosomes condense further in preparation for metaphase I. The centrioles are at opposite poles of the cell. The pairs of homologous chromosomes the bivalentsnow as tightly coiled and condensed as they will be in meiosis, become arranged on a plane equidistant from the poles called the metaphase plate.
Spindle fibers from one pole of the cell attach to one chromosome of each pair seen as sister-chromatidsand spindle fibers from the opposite pole attach to the homologous chromosome again, seen as sister chromatids. Anaphase I begin when the two chromosomes of each bivalent tetrad separate and start moving toward opposite poles of the cell as a result of the action of the spindle.
In anaphase I the sister chromatids remain attached at their centromeres and move together toward the poles. A key difference between mitosis and meiosis is that sister chromatids remain joined after metaphase in meiosis I, whereas in mitosis they separate Fig. In Telophase I the homologous chromosome pairs complete their migration to the two poles as a meiosis essay of the action of the spindle.
Now a haploid set of chromosomes is at each pole, meiosis essay, with each chromosome still having two chromatids. A nuclear envelope reforms around each chromosome set, meiosis essay, the spindle disappears, and cytokinesis follows. In animal cells, cytokinesis involves the formation of a cleavage furrow, resulting in the pinching of the cell into two cells Fig.
After cytokinesis, each of the two progeny cells has a meiosis essay with a haploid set of replicated chromosomes. Meiosis II begins without any further replication of the chromosomes. In prophase II, the nuclear envelope breaks down and the spindle apparatus forms.
Here, the centrioles duplicate. This occurs by separation of the two members of the pair, and then the formation of a daughter centriole perpendicular to each original centriole.
The two pairs of centrioles separate into two centrosomes. The nuclear envelope breaks down, meiosis essay, and the spindle apparatus forms. The chromosomes become arranged on the metaphase plate, much as the chromosomes do in mitosis, and are attached to the now fully formed spindle Fig.
Meiosis essay of the daughter cells completes the formation of a spindle apparatus. Single chromosomes align on the metaphase plate, much as chromosomes do in mitosis. This is in contrast to metaphase I, in which homologous pairs of chromosomes align on the metaphase plate.
For each chromosome, the kinetochores of the sister chromatids face the opposite poles, and each is attached to a kinetochore microtubule coming from that pole. The centromeres separate and the two chromatids of each chromosome move to opposite poles on the spindle.
Introduction to Meiosis - Don't Memorise
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Feb 11, · Meiosis is broken up into into two parts: meiosis I and meiosis II which both consist of four parts. Meiosis I occurs first after DNA replication and consists of prophase I, metaphase I, anaphase I, and telophase I. Prophase I, much like prophase in mitosis, is when the chromosomes shorten and the mitotic spindle forms Meiosis is a scientific process where eukaryotic cells divide themselves to produce gametes for sexual reproduction. During the process of meiosis, the DNA-carrying cell divides itself twice- meiosis I and meiosis II- to produce four gametes. These gametes have distinctive features Mar 23, · Meiosis, on the other hand, comprises of two divisions taking place separately and the chromosomes are reduced by half. The key difference is, whereas mitosis produces two diploid cells, the two cells produced in meiosis are haploid in nature, containing one of each pair of chromosomes. These cells are, usually, involved in blogger.comted Reading Time: 6 mins
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