The Meiosis Is the process of cell division mainly related to the reproduction of sexual cells. In this way, meiosis consists of the partitioning of a cell, initially into two daughter cells, which in turn divide into two more, and so on.
It is the process of cell division responsible for the formation of sex cells or gametes, as are the Spermatozoa And ova. For this reason, meiosis plays a more important role in the reproductive system (Academy, 2017).
The process of cell division by meiosis takes place continuously. It starts when the stem cell separates into two parts, taking on the characteristics of a diploid cell. It soon begins a process in which the cell becomes haploid and is divided into four parts.
As it is possible to obtain four daughter cells from a stem cell, it is said that the meiosis process makes possible the massive production of the cells used during intercourse or sexual intercourse.
Phases of Meiosis
The process of meiosis is composed of two cell divisions, one followed by the other. Therefore, it is said that there is a meiosis I and a meiosis II. The second meiosis occurs only in diploid cells in order to result in only haploid cells.
However, the stages of cell division occurring during both meiosis I and II are the same: prophase, metaphase, anaphase and telophase. These stages are described below (M, 2015).
Meiosis I
Profase I : During this stage, the genetic material can be easily seen in the nucleus of the cell, condensing and taking the form of a diploid chromosome. Here, chromosomes - which are linked together - perform genetic recombination.
Also, the cell membrane disappears. Protein microtubules appear and move to the poles or ends of the cell, allowing an exchange of parts of DNA strands and new genetic material appears that previously did not exist.
The process of combining and exchanging parts of the DNA within the cell allows for new and different genetic combinations and that each cell at the end of the meiosis process has a unique composition.
Metaphase I : The chromosomes inside the cell are directed towards the poles of the cell symmetrically. A line appears in the equatorial zone or center of the cell. It is through this line that the process of cell partitioning will take place.
Anafase I : It is the third stage that takes place during the process of meiosis. During this stage pairs of homologous chromosomes are located at opposite poles of the cellular cytoplasm. At this stage the number of chromosomes is reduced by half in each cell. On the other hand, the dividing line in the center of the cell becomes a pronounced waistline. Here, the process of division is almost complete.
Telophase I : This is the last stage that takes place during the process of meiosis I. Here, the stem cell culminates its partition, resulting in two daughter cells. The cell membrane reappears in each of the resulting cells.
During the telophase, each of the daughter cells has the genetic material necessary and just to be independent. In the same way, once the cell partitioning process reaches this stage, the function state is given, where the second stage of the meiosis process will begin.
Meiosis II
Once the first meiotic division is completed, a short interface takes place again and the resulting cells undergo a new process known as meiosis II.
During this second stage of meiosis the process of replication of the genetic material or DNA does not take place, however, the phases of cell division are the same.
Profase II : The genetic material or chromatin condenses again, and the chromosomes take a visible form once more. Each chromosome is made up of two chromatids joined together by a centromere (point of connection between chromatids). The mitotic spindle and dividing line reappears and the cell membrane fades.
Metaphase II : The chromosomes inside the cell are aligned in the center of the cell, located on its equatorial line. From there, they are pulled by mitotic spindles or microtubules to the ends or poles of the cell.
Anafase II : Each chromatid is separated from the centromere and displaced towards one of the poles of the cell. Each pole of the cell must have the same number of chromatids.
Telophase II : During this stage, each daughter cell culminates its division process, leaving an equal number of haploid chromatids. Here, the cell membrane is re-formed and the chromatin appears again. The division of the cytoplasm of the cell occurs by a new process of cytokinesis, equal to that which takes place during the first stage of the meiotic division.
At the end of this process of meiotic division, four daughter cells must be produced, each containing the same amount of genetic material, composed of half the DNA strands present at the beginning of the cell division process (Educational, 2016).
Characteristics of Meiosis
Unlike the process of mitosis, where the daughter cells have diploid sets of chromosomes, during the process of meiosis each resulting cell finally counts only with a set of haploid chromosomes, that is, simple.
Thus, during the first cell division, the chromosomes that are located in the nucleus of the cell have two chromatids or units of complete chromosomes, which will pass completely (without divisions) and in equal quantity to the daughter cells.
Thus, during the second stage of the meiotic division, the resulting cells will divide again, also separating the diploid structure of the chromosomes, and resulting in the production of haploid cells.
This phenomenon occurs in the sex cells or gametes, since these will be paired during the reproductive process of fertilization, during which the chromosomes will become diploids once the ovum and the sperm join.
Another important feature of meiosis is that it only occurs in organisms where the process of sexual reproduction takes place.
In this way, meiosis is also known as gametogenesis, since it is the process by which gametes are produced, so that they can subsequently participate in the reproductive process.
Gametogenesis
Gametogenesis is the process by which diploid cells (those that present a complete number of chromosomes according to the characteristics of the species), undergo a process of cell division or meiosis with the objective of producing haploid cells (those that Account for half the number of chromosomes typical of the species). These haploid cells are known as gametes.
Gametes are a unique and specialized cell type that play a key role in the reproductive process.
In the case of male gametogenesis, the process of meiosis is known as spermatogenesis, since spermatozoa are produced during this process.
In the case of women, this process is known as oogenesis since oocytes are produced during it (Handel, 1998).
Importance of Meiosis
Thanks to meiosis, the perpetuation of the species is possible. Thanks to this process of cell division, the gametes (eggs and spermatozoa) necessary during the reproductive process are produced.
On the other hand, thanks to the process of genetic recombination that takes place during the meiosis, it is possible that there is a genetic variability among the members of the same species.
This genetic recombination makes possible the permutation of certain characteristics contained within the individuals' DNA in the form of small pieces or chromatids.
This process of genetic permutation is performed randomly and the distribution of genetic characteristics is made random.
This allows for a wide variability in the characteristics that individuals of the same species can inherit (Benavente & Volff, 2009).
Differences meiosis and mitosis
Although both meiosis and mitosis are processes of cell division that take place in all multicellular organisms, they have some different characteristics. Some of these features are listed below:
- During mitosis the stem cell divides into two daughter cells, while during meiosis it is divided into four.
- Mitosis occurs in asexual organisms; on the other hand, meiosis only occurs in organisms with sexual reproduction.
- During mitosis, daughter cells have the same number of chromosomes as the mother cell, contrary to meiosis, where the daughter cells only have half the chromosomes present in the stem cell.
- The goal of mitosis is to generate cells in multicellular organisms and to contribute to the reproduction of unicellular organisms. For its part, the goal of meiosis is to create gametes necessary for the Sexual reproduction .
References
- Academy, K. (2017). Khan Academy . From Meiosis: khanacademy.org
- Benavente, R., & Wolff, J.-N. (2009). Würzburg: Karger.
- Educational, P. (September 13, 2016). Educational Portal . Obtained from Meiosis: portaleducativo.ne74
- Handel, M.A. (1998). Meiosis and Gametogenesis.
- M, C. (March 12, 2015). Definition of . Obtained from Definition of Meiosis: conceptdefinition.de