What is the Importance of MEIOSIS?
As you may already know, cells in the human body can divide by two processes: mitosis and meiosis. Meiosis is a special type of division o cell reproduction which, in mammals, allows eggs and sperm to form. This type of cell division is very important for the creation of our gametes and so that, by joining during fertilization, they can produce a healthy embryo.
In this lesson from a TEACHER we will see what is the importance of meiosis, both for the individuals and the health of their children and from the point of view of the species and its improvement over time. If you want to know more, keep reading!
Index
- What is meiosis? - simple definition
- What is the importance of meiosis? - Reduction of the number of chromosomes
- Genetic variability, another reason for the great importance of meiosis
What is meiosis? - simple definition.
Meiosis is a type of cell reproduction that allows some cells called gametes (ovum and sperm in women and men, respectively). Gametes are cells specialized in reproduction that have very special characteristics, but the most special of all is that they have half the DNA of the rest of the cells of our Body.
As we will see below, meiosis not only allows reduced chromosome copy number in gametes so that, when they unite during fertilization, an individual with the correct number of chromsomes is generated. If this were not the case, each time a fertilization took place, the number of chromsomes would be doubled. During meiosis there is a very important process called genetic recombination, whose task is to "mix" the genes of both chromosomes to generate a new combination (which in biology is called genetic variability) that we can then transmit to the offspring. It would be like making a collage of our genes (inherited from our mother and father), generate a new combination and pass it on to our children.
In this other lesson from a TEACHER you can learn more about the different Types of cell reproduction.
What is the importance of meiosis? - The reduction of the number of chromosomes.
The cells that make up our body are made up of 2 pairs of 23 chromosomes (23 homologous chromosomes), one of which comes from our mother and the other from our father. These, in turn, had 23 pairs of chromosomes that came from their mothers and fathers, so if these cells would have joined directly to form us, we would have twice as many chromosomes! For this, nature has invented a special type of division that reduces the number of chromosomes to 23 and it is only produced to make gametes: meiosis.
During meiosis, the first cell (called oogonia) duplicates the chromosomes. In this way we obtain another cell, called the primary oocyte, which has two copies of the two chromosomes (paternal and maternal). Now, the first meiosis occurs and this cell divides into two and one of the cells takes one copy of each chromosome (polar body) and the other takes the other copy of each chromosome (oocyte secondary). This secondary oocyte undergoes a second meiosis and originates the mature ovum and another polar body and each of these cells carries a chromosome. In this way we manage, starting from a cell with two copies of two chromosomes, to reach a cell with only one copy of a chromosome. Later, two of these cells (egg and sperm) will fuse during fertilization and the number of chromosomes in the formed zygote returns to normal: it will have two copies of each chromosome, one from its mother and one from its father. The polar bodies will be eliminated later, but if you want to know more about them, you may want to review our article Polar bodies: definition and function.
It is very important that the reduction in the number of chromosomes is correct. If the cycles of meiosis or the separation of chromatids (each of the arms of a chromosome) is not adequate, the number of chromosomes is no longer correct and may be higher or lower than normal. This situation, in which a cell has a wrong number of chromosomes is called aneuploidy, and it can occur because you have one copy of more than one chromosome (trisomy), one copy of less than one chromosome (monosomy), or a missing pair of chromosomes (nullisomy). In most cases this will cause serious disorders such as Down syndrome or Turner syndrome.
Genetic variability, another reason for the great importance of meiosis.
As we have already mentioned before, during meiosis a process called meiotic recombination. During this process, the two copies of each chromosome that we have inherited from our father and mother (called homologous chromosomes) associate and exchange genetic material. Imagine that we have a maternal chromosome, with three genes A, B and C that determine hair color, eye color and height respectively; and the homologous paternal chromosome, we will also have those three same genes (for hair color, eyes and height), but instead of being A, B and C they are other varieties: 1, 2 and 3. During recombination, these genes can be exchanged and new combinations can be generated, let's imagine: A, 2 and 3. When that gamete forms an individual, that individual will carry a new combination of genes for hair color, eyes, and height that is different from the parent that formed that gamete.
This process occurs in meiosis I, in which we had two copies of each of the chromosomes so the exchange occurs at the same time between two pairs of homologous chromosomes. Furthermore, the separation of the chromatids (each of the arms of the chromosomes) is random, so it is not known which combination will be transmitted to the next generation.
All this process of recombination and random selection of the chromatids that will form the ovule and the sperm to be fertilized creates a unique, random, very special combination that is almost unrepeatable. This "catalog" of different combinations of genes that all humans have is called in biology genetic variability. The genetic variability of a species is very important since the natural selection he is choosing the best combinations; in this way, species are evolving and are becoming better adapted to the environment and conditions in which they live. The more genetic variability there is, the more combinations natural selection will find, and the more likely one of them is the best.
In case you want to find out more about this topic, we leave you here a video lesson on What is genetics.
Image: SlidePlayer
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