mutation

Biologist

2022

We explain what a mutation is and the levels at which this genetic variation can occur. Also, the types of mutation and examples.

Mutations are key to sustaining high genetic variability.

What is a mutation?

In genetics, a spontaneous and random variation in the sequence of genes that make up the DNA of a living being. This variation introduces specific physical, physiological or other changes in the individual, which may or may not be inherited their descendants.

Mutations can translate into positive or negative changes in the vital performance of the organisms, and in that sense they can promote adaptation and evolution (they can even create new species), or they can develop into genetic diseases or inherited defects. Despite the latter risk, mutations are key to sustaining high genetic variability and allowing life to continue its march.

These types of changes occur for two essential reasons:

  • Spontaneously and naturally, the product of errors in the replication of the genome during the phases of cell division.
  • 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 pathogens, 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, and can be transmitted to offspring if (at least for multicellular living beings) the alteration occurs in the content of the sex cells (gametes).

A mutation can occur at three levels:

  • Molecular (genetic or specific). It occurs in the DNA sequence, that is, in its own nucleotide bases, due to some change in the fundamental elements that compose them.
  • Chromosomal. A segment of chromosome (that is, much more than one gene is altered) and a large number of information.
  • Genomic. It affects a certain set of chromosomes: it causes excesses or shortages of chromosomes, and this substantially varies the entire genome of the organism.

Mutation types

Morphological mutations have to do with the appearance of the body.

Depending on the consequences they have for the organism and its offspring, there are different types of mutations:

  • Morphological mutations. They have to do with the shape or appearance of the body once the development stages are completed: coloration, shape, structure, etc. They can produce mutations that favor adaptation to the environment, such as moths with a color more consistent 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. They interrupt key processes in the maintenance of the organism and, therefore, can cause the death (lethal mutations) or may impair growth and reproduction (deleterious mutations).
  • Conditional mutations. They condition the individual's performance in their biological community, which can lead to permissive conditions (the product of the gene mutated is still functional) or stringent conditions (the mutated gene product loses its viability).
  • Biochemical or nutritional mutations. They 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 metabolism.
  • Mutations due to loss of function. They prevent the correct functioning of a gene, which causes 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, which causes a loss in the absorption of 80% of serotonin.
  • Mutations by gain of function. 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 works bacteria infectious, and is a typical case of evolution. They are rare mutations.

Examples of mutation

Polydactyly is a genetic disorder that produces one or more extra fingers.

Some examples of mutations in humans are:

  • Polydactyly. It is a genetic alteration that occurs during the development of the fetus and that causes the appearance of one or more extra fingers on the hands or feet. These fingers are often dysfunctional and often must be removed.
  • Marfan syndrome. It is caused by defects in a gene called fibrillin-1, which has to do with the genetic information that determines the formation of connective tissue. People with this syndrome have extremely thin build with abnormally long limbs, which exerts abnormal pressure on their aortas, which can develop a heart attack.
  • HIV resistance. There have been very rare cases of people resistant to infection with the Human Immunodeficiency Virus (virus that causes AIDS). This is because a mutation in the CCR5 gene, which the retrovirus recognizes as a "gate" to the human cell, makes certain people "invisible" to infection and prevents them from being easily infected.
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