The 8 Phases Of Meiosis And How The Process Develops
Something wonderful about life is How a single cell can give rise to an entire organism I am talking about the birth of a new living being through sexual reproduction. This is possible by the union of two specialized cells, called gametes (e.g. egg), in fertilization. The surprising thing is that it allows information from the two parents to be transmitted, so the new cell has different genetic material. To achieve this, a different proliferation system than mitosis is necessary, remembering that the result was identical cells. In this case, the method used is meiosis.
In this article We will see what the phases of meiosis are and what this process consists of.
In the case of humans, the cells are diploid, which means that they each have two copies per different chromosome. It is easy; Humans have 23 different chromosomes, but being diploid, we actually have 46 (one extra copy for each). During the phases of meiosis what is achieved are haploid cells that is, they only have one chromosome per type (23 in total).
As happens in mitosis, interphase is present to prepare the cell for its imminent cell division, increasing its size, replicating the genetic content and manufacturing the necessary tools. This is the only similarity of the two processes, since from here everything changes.
Two consecutive divisions: phases of meiosis
Meiosis has the same four phases as mitosis: prophase, metaphase, anaphase and telophase; but they don’t happen in the same way. Furthermore, meiosis performs two cell divisions in a row, which explains why the result is four haploid cells For this reason we speak of meiosis I and meiosis II, depending on which partition we are talking about; and there are actually 8 phases of meiosis, 4 for each division.
Before continuing, two key concepts must be understood. The first is that of homologous chromosomes, and refers to the pair of chromosomes per gap. The second is sister chromatids, which consists of the result of the duplication that has been made of a chromosome during interphase.
Meiosis I
During prophase I, the homologous chromosomes are very close together, allowing parts to be “swapped” between them, as if they were exchanging chromosomes. This mechanism serves to generate more genetic diversity in the offspring Meanwhile, the nucleus is degraded and the chromosome transport pathway is generated: the mitotic spindle.
Metaphase I occurs when the chromosomes are attached to the mitotic spindle. It then enters anaphase I, which is when these are transported to opposite poles. But on this occasion, what separates are the homologous chromosomes and not the sister chromatids, which occurs in mitosis. Once separated, a rapid telophase I begins, where only cytokinesis occurs, that is, the separation into two cells. Without further ado, these new cells enter into a second cell division.
Meiosis II
At this point in the phases of meiosis we have two diploid cells, but the pairs of chromosomes are the replicas (except for the parts exchanged during prophase I) and not the original pair, since what has been separated are the homologous chromosomes .
As this is a new cell division, the cycle is the same with some differences, and this phase is more similar to what occurs in mitosis. During prophase II the mitotic spindle re-forms so that in metaphase II it joins the chromosomes at their center and, now, during anaphase II the sister chromatids separate towards opposite poles. During telophase II, the nucleus forms to contain the genetic content and the separation of the two cells occurs.
The end result is four haploid cells, since each one only has one copy per chromosome. In the case of humans, By this mechanism, sperm or eggs are generated depending on the gender, and these cells contain 23 chromosomes, unlike the 46 chromosomes of the rest of the cells (23×2).
sexual reproduction
The objective that has been achieved throughout the phases of meiosis is to generate haploid cells, called gametes, which can give rise to a new organism This is the foundation of sexual reproduction, the ability for two individuals of the same species to have offspring by matching their genetic content.
For this reason, it is logical that these cells are haploid, so that at the moment of fertilization, which is the union of the two types of gametes (in the human case of the sperm and the egg), a new diploid cell is generated whose genetic material It is formed by the pairing of chromosomes from each gamete.
