The 8 phases of meiosis and how the process unfolds

This process is the one that explains how new organisms are originated by the union of gametes.

A wonderful thing 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 made possible by the union of two specialized cells, called gametes (e.g. egg), at fertilization. The amazing thing is that it allows the transmission of information from the two parents, so that the new cell has different genetic material. To achieve this requires a different system of proliferation to mitosis, which remember that its result was identical cells. For 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.

Forming haploid cells

In the case of humans, cells are diploid, which means that they each have two copies per different chromosome. It's easy; humans have 23 different chromosomes, but being diploid, we actually have 46 (one extra copy per chromosome). During the phases of meiosis what we get are haploid cells, i.e., they have only one chromosome per chromosome.that is to say, they only have one chromosome per type (23 in total).

As in mitosis, interphase is present to prepare the cell for its impending cell divisionThis is the only similarity between the two types of cells, increasing their 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 do not follow one another in the same way. In addition, meiosis makes two cell divisions in a row, which explains why it results in four haploid cells.. For this reason we speak of meiosis I and meiosis II, depending on which division we are talking about; and in reality there are 8 phases of meiosis, 4 for each division.

Before continuing, two key concepts must be understood. The first is homologous chromosomes.and refers to the pair of chromosomes per gap. The second is sister chromatids, which is the result of the duplication that has been made of a chromosome during interphase.

Meiosis I

During prophase I, homologous chromosomes are in close proximity, allowing them to "swap" parts with each other, 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, the mitotic spindle, is generated.

Metaphase I occurs when the chromosomes are attached to the mitotic spindle. It then enters anaphase I when they are transported to opposite poles. But this time, what separates are the homologous chromosomes and not the sister chromatids, which occurs in mitosis. Once separated, begins a rapid telophase Ibegins, where only cytokinesis occurs, that is, the separation into two cells. With no time for more, these new cells enter a second cell division.

Meiosis II

At this point in the meiosis phases we have two diploid cells, but the chromosome pairs are the replicas (except for the parts exchanged during prophase I) and not the original pair, since what has separated are the homologous chromosomes.

Since this is a new cell division, the cycle is the same with some difference, and this phase is more like what happens in a mitosis. During prophase II the mitotic spindle is re-formed during metaphase II, the chromosomes are joined at their center and, now, during anaphase II, the sister chromatids are separated towards opposite poles. During telophase II, the nucleus is formed to contain the genetic content and the separation of the two cells takes place.

The end result is four haploid cells, each having only one copy per chromosome. In the case of humans, by this mechanism, sperm or egg cells are generated, depending on the gender.Depending on the gender, these cells contain 23 chromosomes, as opposed to the 46 chromosomes of the rest of the cells (23x2).

Sexual reproduction

The objective that has been achieved throughout the phases of meiosis is that of generate haploid cells, called gametes, which can give rise to a new organism.. This is the basis of sexual reproduction, the ability of two individuals of the same species to have offspring by matching their genetic content.

It is therefore 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 is formed by the pairing of chromosomes from each gamete.