We explain what a mutation is and the levels at which this genetic variation can occur. Also, the types of mutation and examples.
What is a mutation?
In genetics it is called a mutation a spontaneous and unpredictable variation in the sequence of genes that make up the DNA of a living being, which introduces specific changes of a physical, physiological or other nature in the individual, which may or may not be inherited from their descendants.
Mutations can translate into positive or negative changes in the vital performance of organisms, and in that sense they can promote adaptation and evolution (even creating new species in the long run), or they can become genetic diseases or hereditary defects. Despite this last risk, mutations are key to sustaining high genetic variability and keeping life going.
This type of change occurs for two essential reasons: spontaneously and naturally, the product of errors in the replication of the genome during the phases of cell replication; or externally, due to the action of various types of mutagens on the body, such as ionizing radiation, certain chemical substances and the action of some viral organisms, among others.
Most of the mutations that living beings experience are of the recessive type, that is, they do not become manifest in the individual in which they originate, but remain inactive and unnoticed, although it can be transmitted to the offspring in the event that (at least for multicellular living beings) the alteration occurs in the content of the sex cells (gametes).
Mutations can occur at three levels:
- Molecular (genetic or specific). They occur in the chemical bases of DNA, that is, in their own nitrogenous bases, due to some change in the fundamental elements that compose them.
- Chromosomal. A chromosome segment is altered, that is, much more than a gene, and in this sense large amounts of information can be lost, duplicated or moved.
- Genomic. It affects a certain set of chromosomes, causing excesses or shortages of them, and substantially varying the entire genome of the organism.
Mutation types
Depending on the consequences it has for the body and its offspring, we can talk about:
- Morphological mutations. They are those that have to do with the shape or appearance of your body, once the development stages are completed: coloration, shape, structure, etc. They can produce convenient mutations, such as a moth with a color more in line with the environment and therefore more conducive to camouflage and survive, or they can produce malformations or diseases, such as human neurofibromatosis.
- Lethal and deleterious mutations. In this group are the mutations that interrupt key processes in the maintenance of the organism and that therefore can cause death (lethal) or a significant disability to grow and reproduce (deleterious).
- Conditional mutations. They are so called those that condition the performance of the individual in their biological community, which can cause permissive conditions (the product of the mutated gene is still functional) or restrictive conditions (the product of the mutated gene loses its viability).
- Biochemical or nutritional mutations. Those that affect the production of a certain biochemical compound necessary to fulfill specific functions, such as enzymes, metabolites or other elements necessary, above all, for cellular nutrition. This type of organisms require the addition of said enzyme or compound to be able to perform the function normally.
- Mutations due to loss of function. These are mutations that prevent the correct functioning of a gene, causing the organism that presents it to lose some specific function. This is the case of unipolar depression in humans, caused by a mutation in the hTPH2 gene that causes a loss in the absorption of 80% of serotonin.
- Mutations by gain of function. They are rare mutations, in which a change in DNA adds functions to the modified gene and therefore to the organism that presents it. This is how the antibiotic resistance of some infectious bacteria operates, and it is a typical case of evolution.
Examples of mutation
Some examples of mutations in humans are:
- Polydactyly. Known as Bardet-Biedl or Greig Cephalopolysyndactyly syndrome, it is a genetic disorder during the development of the fetus that causes the appearance of one or more extra fingers on the hands or feet, which are usually dysfunctional and often must be removed.
- Marfan syndrome. The gene that causes this disease is transmitted through the father, as a spontaneous mutation, and has to do with the genetic information that determines the formation of connective tissue. Those who suffer from the disease have extremely thin build with abnormally long limbs, which exerts abnormal pressure on their aortas, which can lead to heart attack.
- HIV resistance. There have been very rare cases of people resistant to infection with the AIDS virus, and this is due to the fact that a mutation in the CCR5 gene, which the retrovirus recognizes as a “gate” to the human cell, makes them “invisible” to infection, thus not being able to be easily infected.