Mutation (Meaning and Explanation)

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

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What is a mutation?

In genetics, a mutation is called 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 to their descendants.

The mutations can translate into positive or negative changes in the vital performance of organisms and in that sense they can drive adaptation and evolution (they can even create new species), or they can become genetic diseases or hereditary defects. Despite this last risk, mutations are key to sustaining high genetic variability and allowing life to continue.

These types of changes occur for two essential reasons:

Spontaneously and naturally, a product of errors in genome replication during the phases of cell division.
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 pathogens, among others.

Most of the mutations that living beings experience are recessive, that is, they do not become manifest in the individual in which they originate but rather 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 sexual cells (gametes).

A mutation can occur at three levels:

Molecular (genic 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 chromosome segment is altered (that is, much more altered than a gene) and a large amount of information can be lost, duplicated or moved.
Genomic . It affects a specific set of chromosomes: it causes excesses or lacks of chromosomes, and this substantially varies the entire genome of the organism.

Types of mutation

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 stages of development have been completed: coloration, shape, structure, etc. They can produce mutations that favor adaptation to the environment, such as moths with a color more in line with the environment (and, therefore, more conducive to camouflage and survival), 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 death (lethal mutations) or can generate an impediment in growth and reproduction (deleterious mutations).
Conditional mutations . They condition the performance of the individual in its biological community, which can cause permissive conditions (the mutated gene product is still functional) or restrictive 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.
Loss-of-function mutations . They prevent the correct functioning of a gene, which causes the organism that has it to lose some specific function. This is the case of unipolar depression in humans, caused by a mutation of the hTPH2 gene, which causes a loss in the absorption of 80% of serotonin.
Gain-of-function mutations . 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 it is a typical case of evolution. They are rare mutations.

Examples of mutation

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 usually 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. Those who suffer from this syndrome have an extremely thin build with abnormally long limbs, which puts abnormal pressure on their aortas, which can lead to 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 “door” to the human cell, makes certain people “invisible” to infection and prevents them from being easily infected.