The chromosome permutation It is the phenomenon by which, during the formation of sex cells, chromosomes are randomly distributed among daughter cells. This process contributes especially to the increase in the genetic variability of the offspring when sexual reproduction occurs..
Most eukaryotic organisms reproduce sexually and this generally involves the fusion of a pair of special cells from two different organisms. These cells are the sex cells that are almost always known as gametes: sperm (male) and egg (female).
Gametes are haploid cells (n), that is, they have half the chromosomal load with respect to the individual that gave rise to them. They come from other cells known as germ cells, which divide by a special type of reductive cell division known as meiosis.
Humans, for example, are diploid organisms (2n), which means that we have two copies of each chromosome (homologous chromosomes), each inherited from one of our parents through the fusion of their gametes during sexual reproduction ( fertilization).
In the process of formation of the sex cells of our parents, each gamete randomly received one of the two chromosomes of the cell that gave it origin, which also went through a process of genetic recombination that mixed the DNA of the chromosomes of each parent.
Although the concept of "chromosomal permutation" is not widely used in the literature, it is used to refer to the random segregation of homologous chromosomes between daughter cells, which takes place during the metaphase of meiosis I.
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Meiosis is a type of cell division very similar to mitosis, which is the type of division by which the cells of our body and the cells of the body of most living beings multiply.
During meiosis, however, a halving in the number of chromosomes occurs, which is why it is also known as "reductional division.".
The formation of sex cells or gametes occurs through meiosis and the restitution of the genetic load of an organism occurs thanks to the fusion of two gametic nuclei formed by meiosis and the formation of the zygote after fertilization.
Meiosis involves two successive rounds of chromosome segregation. In meiosis I, homologous chromosomes are duplicated and then separated, which significantly differentiates this process from mitosis, where it is the copies of these chromosomes (the sister chromatids) that separate.
Before the separation of the homologous chromosomes takes place, a phenomenon of physical approach and exchange of genetic material between them occurs, an event known as recombination, whose ultimate goal is to increase genotypic variations in offspring.
In meiosis II, a second round of duplication does not occur, but the sister chromatids are separated from each other, as occurs during mitosis, which implies the formation of 4 haploid cells (with half the chromosomal load).
Chromosome permutation occurs during metaphase and anaphase of meiosis I, that is, metaphase I and anaphase I, after crossover or recombination has taken place.
At this stage of the meiotic process, the homologous chromosomes and their copies, thanks to the association of their kinetochoric complexes in the centromere with the fibers of the spindle, are aligned in the equatorial plane, being arranged or oriented randomly towards one of the two poles of the cell.
Once ordered, the homologous chromosomes are "pulled" and distributed towards the daughter cells during anaphase I, this implies that the resulting cells receive different combinations of chromosomes..
From the mathematical point of view, a permutation consists of a variation of the combination or the order of the elements of a set.
In the genetic context, this term is used to refer to the multiple combinatorial possibilities that can occur between chromosomes during meiosis I, when the sex cells receive the genetic material that corresponds to them.
The number of possible combinations of these chromosomes depends on the species, since the chromosomal load of each species is different, as well as the ploidy (the number of copies of each chromosome that each cell has).
For human beings, for example, who are diploid organisms (2n) with 23 pairs of chromosomes, the number of combinations is 2 raised to the power 23, which is equal to more than 8 million 300 thousand combinations, which is why says that this phenomenon works in increasing genetic variability.
Chromosomal permutation, defined as we have seen above, fulfills the main function of increasing genetic variability.
Recombination, mutations, and chromosomal permutations, which are closely related to sexual reproduction and therefore meiosis, are the most important mechanisms in nature that lead to genotypic differences found between individuals in populations..
The importance of this variability is related to the increase in the possibilities of adaptation, since the emergence of new combinatorial variables can mean the appearance of new phenotypic characteristics that can, depending on the environmental conditions, be favorable or unfavorable..
Due to the randomness induced by the phenomenon of chromosomal permutation, human populations are considerably diverse, and it is that, with very few exceptions, there are no two identical individuals, although they have been conceived by the same parents.
This is not only true for humanity, but also for a large number of organisms that reproduce sexually, for which environmental variations can impose stronger selective pressures than for humans, thus the presence of certain variations in the population can mean an advantage.
In any natural population, the presence of genotypic variants is essential to ensure the existence of the species, since significant extinctions could occur if conditions were to change suddenly and all individuals of a species were equally susceptible..
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