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2.8. Mutations. Relations with evolution

Genetic mutation and its relationship with evolution

Genetic mutation concept

If there is a change in the genetic information contained in the DNA of cells, it is said that a genetic mutation occurs. These alterations can occur in DNA duplication or in the natural mechanisms of repair of duplication errors, or by failures in the distribution of chromosomes during cell division. But they can also be due to other mutagenic agents, such as radiation, chemical substances, etc.

Mutations can range from the substitution of one nitrogen base for another, to changes in the normal chromosome number of a species. These alterations can cause changes in the proteins that have to be synthesized, which would generate changes in the characteristics of the organism.

For the mutation to be passed on to offspring and be heritable, it has to occur in the gametes (eggs and sperm). If the mutation affects a somatic (non-sexual) cell, that individual's mutation will not be passed on to offspring.

Types of mutations

Mutations can be classified in several ways.

Depending on the affected DNA, these mutations are distinguished:

  • Gene or point mutation. They are mutations that affect only the nucleotide sequence of a gene. Changes are produced in the nitrogenous bases, one being replaced by another, or losing or gaining some nitrogenous base, which causes changes in the structure of DNA.

Distintos tipos de mutaciones génicas

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  • Chromosomal mutation. Alterations in the structure of the chromosome occur, either because some segment of a chromosome has been lost, fragments are exchanged with other chromosomes, etc.

Tipos de mutaciones cromosómicas: deleción, duplicación, inversión, inserción, translocación

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  • Genomic mutation. It affects the entire chromosome, altering the number of chromosomes (genome) of the individual, with some chromosome more or less than the normal number of chromosomes of its species.

Depending on the origin of the mutation, these mutations are distinguished:

  • Spontaneous mutation. They are not frequent, and are produced by natural causes, such as an error in DNA replication.
  • Induced mutationCaused by exposure to certain mutagens, present in the environment, such as radiation (gamma rays, UV, X), chemical substances (nitrous acid, tobacco smoke), or some viruses.

Consequences of mutations

The main consequence of mutations is the appearance of new alleles that will give rise to different phenotypes.

The mutations can be:

  • Neutral or harmless mutations, if they do not produce effects, neither benefits nor harm, to the organism that has them.
  • Negative mutations, if they cause harm to the individual who carries them, can even cause death.
  • Beneficial mutations. The new phenotypes can increase the probability of survival of the organism and of reproducing, since they provide better characteristics that allow it to adapt to the environment.

The  natural selection makes them more likely to survive those individuals that are better adapted to the conditions of the environment, and that those who are less well adapted, have more difficulty surviving.

Mutations are of biological importance, since they are a source of variability or genetic diversity of populations and allow the evolution of species.

Activity: Genetic diseases.


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