The human body is made up of 37 trillion cells. It is surprising that this immense amount originates from a single cell that is conceived during fertilization. This is possible due to the ability of cells to self-reproduce, a process that involves dividing in two. Little by little, the aforementioned amount is reached, forming the different organs and types of cells.
Now, there are two basic mechanisms by which cells can reproduce: mitosis and meiosis. We’ll see now the differences between mitosis and meiosis and their characteristics
We have seen that little by little, a few cells can give rise to an entire organism, whether it is a human being or an immense whale. In the case of human beings, These are diploid eukaryotic cells that is, they have one pair per chromosome.
The chromosome structure is the most compact and condensed form that DNA can present together with structural proteins. The human genome is made up of 23 pairs of chromosomes (23×2). This is important information to know one of the main differences between mitosis and meiosis, the two types of cell division that exist.
The eukaryotic cell cycle
Cells follow a series of sequential patterns for their division. This sequence is called the cell cycle, and consists of the development of four coordinated processes: cell growth, DNA replication, distribution of duplicated chromosomes and cell division This cycle differs in some points between prokaryotic cells (bacteria) or eukaryotes, and even within eukaryotes there are differences, for example between plant and animal cells.
The cell cycle in eukaryotes is divided into four stages: G1 phase, S phase, G2 phase (all of them are grouped in interphase), G0 phase and M phase (Mitosis or Meiosis).
1. Interface
This group of stages is intended to prepare the cell for its imminent division into two following the following phases:
Throughout the interface, there are several checkpoints to verify that the process is being carried out correctly and that there are no errors (for example, that there is no bad duplication). If there is any problem, the process stops and an attempt is made to find a solution, since cell division is a process of vital importance; everything has to go well.
2. G0 Phase
Cell proliferation is lost when cells become specialized so that the growth of the organism is not infinite. This is possible because cells enter a resting stage called G0 phase, where they remain metabolically active but do not present cell growth or replication of genetic content, that is, they do not continue in the cell cycle.
3. Phase M
It is in this phase that cell division occurs and mitosis or meiosis develops well
Differences between mitosis and meiosis
In the division phase is when either mitosis or meiosis occurs.
Mitosis
It is the typical cell division of a cell giving rise to two copies As with the cycle, mitosis has also traditionally been divided into different stages: prophase, metaphase, anaphase and telophase. Although for a simpler understanding, I will describe the process in general and not for each phase.
At the beginning of mitosis, the genetic content is condensed into the 23 pairs of chromosomes that make up the human genome. At this time, the chromosomes are duplicated and form the typical X image of chromosomes (each side is one copy), joined in the middle through a protein structure known as the centromere. The nuclear membrane that encloses DNA is degraded so that the genetic content is accessible.
During the G2 phase, different structural proteins have been synthesized, some of them double. They are called centrosomes which are each placed at a pole opposite each other of the cell.
Microtubules extend from the centrosomes, protein filaments that constitute the mitotic spindle and that join the centromere of the chromosome. to stretch one of the copies to one of the sides breaking the X structure.
Once on each side, the nuclear envelope reforms to enclose the genetic content, while the cell membrane is strangled to generate two cells. The results of mitosis are two sister diploid cells since their genetic content is identical.
Meiosis
This type of cell division only occurs in the formation of gametes , which in the case of humans are sperm and eggs, cells that are responsible for shaping fertilization (they are the so-called germ cell line). In a simple way, it can be said that meiosis is as if two consecutive mitosis were carried out.
During the first meiosis (meiosis 1) a process similar to that explained in mitosis occurs, except that the homologous chromosomes (the couple) can exchange fragments between them by recombination. This does not occur in mitosis, since in this they never come into direct contact, unlike what occurs in meiosis. It is a mechanism that offers more variability to genetic inheritance. Besides, what separates are the homologous chromosomes, and not the copies
Another difference between mitosis and meiosis occurs with the second part (meiosis 2). After having formed two diploid cells, they divide again immediately Now the copies of each chromosome are separated, so the final result of meiosis is four haploid cells, since they only have one chromosome of each (not pairs), to allow new pairings to form between the chromosomes during fertilization. of parents and enrich genetic variability.
To summarize the differences between mitosis and meiosis in humans, we will say that the final result of mitosis is two identical cells with 46 chromosomes (pairs of 23), while in the case of meiosis there are four cells with 23 chromosomes each. one (without pairs), in addition to the fact that its genetic content can vary by recombination between homologous chromosomes.
