The chromosomal permutation is a process of random distribution of chromosomes during cell division sex (meiosis), which contributes to the generation of new chromosomal combinations.
It is a mechanism that confers an increase in variability to daughter cells due to the combination of maternal and paternal chromosomes.
Reproductive cells (gametes) are produced by meiosis, which is a type of cell division similar to mitosis. One of the differences between these two types of cell division is that events occur in meiosis that increase the genetic variability of the offspring.
This increase in diversity is reflected in the distinctive features presented by the individuals generated in fertilization. For this reason children do not look exactly the same as their parents, nor do siblings of the same parents look the same to each other, unless they are identical twins.
This is important because the generation of new combinations of genes increases the genetic diversity of the population and, consequently, there is a wider range of possibilities for it to be able to adapt to different environmental conditions.
Chromosome permutation occurs in metaphase I
Each species has a defined number of chromosomes, in humans there are 46 and corresponds to two sets of chromosomes.
Therefore, the genetic load in humans is said to be “2n”, since one set of chromosomes comes from the mother's (n) eggs and the other from the father's (n) sperm.
Sexual reproduction involves the fusion of the female and male gametes, when this occurs the genetic load is doubled, generating a new individual with a load (2n).
Human gametes, both female and male, contain a single set of genes made up of 23 chromosomes, which is why they have “n” genetic load.
Two successive cell divisions occur in meiosis. Chromosome permutation occurs in one of the stages of the first division, called metaphase I. Here, the homologous paternal and maternal chromosomes line up and then be randomly divided among the resulting cells. It is this randomness generates variability.
The number of possible combinations is 2 raised to n, which is the number of chromosomes. In the case of humans n = 23, then 2²³ would remain, which results in more than 8 million possible combinations between the maternal and paternal chromosomes.
Biological importance
Meiosis is an important process to keep the number of chromosomes constant from generation to generation.
For example, the mother's eggs are generated from meiotic divisions of the cells of the ovaries, which were 2n (diploid) and after meiosis they became n (haploid).
A similar process generates n (haploid) sperm from testicular cells, which are 2n (diploid). When the female gamete (n) is fertilized with the male gamete (n), diploidy is restored, that is, a 2n charged zygote is generated that will later become an adult individual to repeat the cycle.
Meiosis also has other important mechanisms that allow variability to be further increased by creating different combinations of genes through a mechanism of genetic recombination called crossing over (or crossing over, in English). Thus, each gamete that is produced has a unique combination.
Thanks to these processes, organisms increase genetic diversity within their populations, which increases the chances of adapting to variations in environmental conditions and the survival of the species.
References
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