What is a mutation?

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

1. What is a mutation?

Genetic called mutation  variation spontaneous and unpredictable sequence of genes that comprise the DNA of a living being , which introduces temporary changes of physical, physiological or other type in the individual, which may or may not be inherited to Your descendants.

Mutations  can translate into positive or negative changes in the vital performance of organisms , and in that sense they can boost adaptation and evolution (even creating new species in the long run), or they can become genetic diseases or inherited defects. Despite this last risk, mutations are key to sustaining high genetic variability and for life to continue its march.

These types of changes occur for two essential reasons: spontaneously and naturally, due to errors in genome replication during the phases of cell replication; or externally, due to the action of mutagens of various types on the organism, 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 a recessive type, that is, they do not become manifest in the individual in which they originate, but remain inactive and inadvertent , although they can be transmitted to the offspring in the event that (at least for multicellular living beings) the alteration occurs in the content of sex cells (gametes).

Mutations can occur at three levels:

• Molecular (gene or specific) . They occur in the chemical bases of DNA, that is, in their own nitrogen bases, due to some change in the fundamental elements that compose them.
• Chromosomal . A segment of chromosome is altered , that is, much more than a gene, and in that sense large amounts of information can be lost, duplicated or relocated.
• Genomic . It affects a certain set of chromosomes, causing excesses or lack thereof, and substantially varying the entire genome of the organism.

2. Types of Mutation

Depending on the consequences it has for the organism 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 stages of development are completed: coloring, shape, structure, etc. They can produce suitable mutations, such as that of a colored moth 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 therefore can cause death (lethal) or a significant disability to grow and reproduce (deleterious).  
• Conditional mutations . These are called those that condition the performance of the individual in their biological community, and 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 nutritive mutations . Those that affect the production of a certain biochemical compound necessary to fulfill specific functions, such as enzymes , metabolites or other elements necessary, especially for cell nutrition. These types of organisms require the addition of said enzyme or compound 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 of the hTPH2 gene that causes a loss in the absorption of 80% of serotonin.
• Mutations by function gain . 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 antibiotic resistance of some infectious bacteria operates , and is a typical case of evolution.

3. Mutation Examples

Some examples of mutations in humans are:

• Polydactyly . Known as Bardet-Biedl or Greig Cephalopolysyndactyly syndrome, it is a genetic alteration during the development of the fetus that causes the appearance of one or several extra fingers on the hands or feet, which are usually dysfunctional and must often be removed.
• Marfan syndrome . The gene that causes this disease is transmitted by the father’s pathway, 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 an abnormal pressure on their aortas, and 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 because a mutation in the CCR5 gene, which the retrovirus recognizes as a “door” to the human cell, makes them “invisible” to the infection, and thus cannot be easily infected.