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StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The body is made up of trillions that somatic cells v the capacity to division into similar daughter cells facilitating organismal growth, repair, and solution to the transforming environment. This process is called “mitosis.” In the gametes, a different kind of cell department occurs referred to as “meiosis.” The result of meiosis is the development of daughter cells, either sperm or egg cells, through reduction division which results in a haploid complement of chromosomes so the on authorized with an additional sex cabinet at fertilization a new diploid chromosomal complement is revitalized in the fertilized egg.<1><2><3>

Genomic diversity and genetic sport is developed through the procedure of meiosis as result of chromosomal recombination and also independent assortment. Every daughter cell developed is gene half-identical to that of its parental cell however distinctly different from its parental cell and other daughter cells.<4><5>


Cellular

The genome is encoded by the chemistry sequence of DNA nucleotides in ~ our cells. If stretched from end to end, the DNA in one cell would span around 3 meters. In order to fit right into each cell, the DNA is condensed by proteins to produce “chromatin,” a complicated of DNA and proteins. Somatic human cells save on computer 23 combine chromosomes or 46 full chromosomes. 46 is taken into consideration the “diploid” number (2n), when 23 is thought about the “haploid” number (1n), or fifty percent the diploid number.<6><7>


Function

Meiosis is essential for creating genomic diversity in a species. It perfect this primarily through 2 processes: elevation assortment and also crossing end (recombination).


The law of live independence assortment states that the arbitrarily orientation the homologous chromosome pairs during metaphase I permit for the manufacturing of gametes with many different assortments of homologous chromosomes. Because that example, tetrads comprise chromosomes 1A/1B and also 2A/2B can create 2 different variations in daughter cells: 1A2A, 1A2B, 1B2A, or 1B2B. Through 46 cell in the person body, about 8 million various variations have the right to be produced.
Crossing over refers to a phenomenon that takes place during prophase I. As soon as homologous chromosomes come with each other to form tetrads, the eight of the chromatids can swap at random, producing many much more possibilities for genetic variation the the gametes.

Mechanism

There room 2 components to the cell cycle: interphase and also mitosis/meiosis. Interphase have the right to be further subdivided into expansion 1 (G1), synthesis (S), and Growth 2 (G2). During the G phases, the cabinet grows by creating various proteins, and also during the S phase, the DNA is replicated so the each chromosome contains two identical sister chromatids (c). Mitosis includes 4 phases: prophase, metaphase, anaphase, and telophase. 

Mitosis


Metaphase: The chromosomes line up follow me the metaphase plate. Microtubules originating indigenous the centrosomes at the 2 the opposite poles the the cell connect to the kinetochores of each chromosome.
Telophase: The chromosomes gather at the poles of the cell, and also the cabinet divides via cytokinesis developing 2 daughter cells. The atom envelope reappears, the spindle device disappears and the chromosomes de-condense ago into chromatin.

The cell can now go into Interphase where it grows and replicates that DNA in preparation for division, yet again.

Meiosis goes through all 5 phases of the cabinet cycle twice, with modified mechanisms that ultimately develop haploid cells rather of diploid. In sperm cells, the male gametes, meiosis proceeds in the following manner:

Meiosis I


Prophase I: The atom envelope breaks down. The dyed condenses into chromosomes. Homologous chromosomes include the 2 chromatids come together to type tetrads, involvement at your centromeres (2n 4c). This is as soon as “crossing over” occurs, which creates genetic variation.
Metaphase I: The tetrads line up along the metaphase plate. Microtubules originating from the centrosomes at the 2 the contrary poles of the cell affix to the kinetochores of each chromosome.
Telophase I: The chromosomes conference at the poles of the cell, and the cell divides via cytokinesis developing 2 daughter cells (1n 2c). The nuclear envelope reappears, the spindle device disappears and the chromosomes de-condense ago into chromatin.

Interkinesis/Interphase II 

There is a quick pause in between each ring of meiosis providing time because that the cabinet to replenish proteins; however, there is no S phase.

Meiosis II


Prophase II: In every of the daughter cells, a new spindle device forms, the nuclear envelope breaks down, and also the chromatin condenses right into chromosomes again.
Metaphase II: The chromosomes line up follow me the metaphase plate. Microtubules originating native the centrosomes at the 2 the contrary poles the the cell attach to the kinetochores of each chromosome.
Anaphase II: sister chromatids separate and also are traction by the microtubules to opposite poles the the cell.
Telophase II: The chromosomes gather at the 2 poles that the cell and the cabinet divides via cytokinesis forming 2 daughter cell (1n 1c) from each of the two cells native meiosis I. The atom envelope reappears, the spindle apparatus disappears and the chromosomes de-condense earlier into chromatin.

In egg cells, the female gametes, meiosis adheres to the same basic phases with just a slim variation. During telophase I, the cytoplasm divides unequally, producing a bigger daughter cell and also a smaller polar body. The polar body and the daughter cell both then get in meiosis II. In telophase II, the cytoplasm the the daughter cabinet again divides unequally and also creates a daughter cell and another polar body. In addition, the polar human body from meiosis ns divides and also forms 2 smaller sized polar bodies. After ~ meiosis is completed, over there is one daughter cell (1n, 1c) and 3 polar body (1n 1c). The polar body disintegrate together they carry out not have enough cytoplasm and proteins to survive as gametes.


Clinical Significance

Clinically, errors in meiosis deserve to create countless life-threatening outcomes. The most common error the meiosis is nondisjunction, once chromatids fail to separate during either anaphase i or II, producing imbalances in the number of chromosomes in each daughter cell. Most imbalances are incompatible v life, yet some will result in viable offspring through a spectrum the developmental disorders. This medical problems include down syndrome, Patau syndrome, Edwards syndrome, Klinefelter syndrome, Turner syndrome, Triple X syndrome, and also XYY syndrome.

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