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You are watching: During cytokinesis in the female what divides unequally

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


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Introduction

The body is made up of trillions of somatic cells through the capacity to division into the same daughter cell facilitating organismal growth, repair, and response to the transforming environment. This process is dubbed “mitosis.” In the gametes, a different type of cell division occurs dubbed “meiosis.” The outcome of meiosis is the production of daughter cells, either sperm or egg cells, through reduction department which outcomes in a haploid complement of chromosomes so the on authorized with an additional sex cabinet at fertilization a new diploid chromosomal match is revitalized in the fertilized egg.<1><2><3>

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


Cellular

The genome is encoded by the chemistry sequence that DNA nucleotides in ~ our cells. If stretched from finish to end, the DNA in one cell would certainly span about 3 meters. In order come fit into each cell, the DNA is condensed by proteins to produce “chromatin,” a complicated of DNA and proteins. Somatic human being cells contain 23 paired chromosomes or 46 full chromosomes. 46 is considered the “diploid” number (2n), when 23 is considered the “haploid” number (1n), or fifty percent the diploid number.<6><7>


Function

Meiosis is crucial for creating genomic diversity in a species. It accomplishes this generally through 2 processes: independent assortment and crossing end (recombination).


The law of live independence assortment says that the arbitrarily orientation the homologous chromosome pairs during metaphase I allow for the production of gametes with countless different assortments of homologous chromosomes. For example, tetrads comprise chromosomes 1A/1B and also 2A/2B can produce 2 different variations in daughter cells: 1A2A, 1A2B, 1B2A, or 1B2B. With 46 cell in the human body, around 8 million different variations have the right to be produced.
Crossing over describes a phenomenon that takes place during prophase I. Once homologous chromosomes come with each other to type tetrads, the arms of the chromatids have the right to swap at random, producing many much more possibilities for genetic variation the the gametes.

Mechanism

There are 2 parts to the cell cycle: interphase and also mitosis/meiosis. Interphase deserve to be further subdivided into growth 1 (G1), synthesis (S), and also Growth 2 (G2). During the G phases, the cell grows by developing various proteins, and also during the S phase, the DNA is replicated so that each chromosome contains two identical sister chromatids (c). Mitosis has 4 phases: prophase, metaphase, anaphase, and also telophase. 

Mitosis


Metaphase: The chromosomes line up along the metaphase plate. Microtubules originating indigenous the centrosomes in ~ the 2 opposite poles that the cell affix to the kinetochores of every chromosome.
Telophase: The chromosomes gather at the poles of the cell, and also the cell divides via cytokinesis forming 2 daughter cells. The atom envelope reappears, the spindle apparatus disappears and the chromosomes de-condense earlier into chromatin.

The cell deserve to now enter Interphase whereby it grows and also replicates its DNA in ready for division, however again.

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

Meiosis I


Prophase I: The atom envelope division down. The chromatin condenses into chromosomes. Homologous chromosomes containing the two chromatids come together to type tetrads, joining at their centromeres (2n 4c). This is when “crossing over” occurs, i m sorry creates genetic variation.
Metaphase I: The tetrads line up follow me the metaphase plate. Microtubules originating from the centrosomes at the 2 the opposite poles the the cell attach to the kinetochores of every chromosome.
Telophase I: The chromosomes gather at the poles the the cell, and also the cell divides via cytokinesis developing 2 daughter cell (1n 2c). The nuclear envelope reappears, the spindle apparatus disappears and the chromosomes de-condense ago into chromatin.

Interkinesis/Interphase II 

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

Meiosis II


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

In egg cells, the female gametes, meiosis complies with the same general phases with only a slim variation. During telophase I, the cytoplasm divides unequally, developing a larger daughter cell and a smaller polar body. The polar body and the daughter cabinet both then go into meiosis II. In telophase II, the cytoplasm of the daughter cabinet again divides unequally and creates a daughter cell and another polar body. In addition, the polar body from meiosis i divides and also forms 2 smaller sized polar bodies. After ~ meiosis is completed, there is one daughter cabinet (1n, 1c) and also 3 polar body (1n 1c). The polar body disintegrate together they do not have enough cytoplasm and also proteins to survive as gametes.


Clinical Significance

Clinically, errors in meiosis deserve to create numerous life-threatening outcomes. The most common error of meiosis is nondisjunction, as soon as chromatids fail come separate during either anaphase i or II, creating imbalances in the variety of chromosomes in every daughter cell. Most discrepancies are incompatible with life, however some will an outcome in viable offspring through a spectrum that developmental disorders. These medical problems include under syndrome, Patau syndrome, Edwards syndrome, Klinefelter syndrome, Turner syndrome, Triple X syndrome, and XYY syndrome.

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