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11.1. Mutations

Genetic mutations

The DNA as hereditary material transmitted with great fidelity to the next generations. Although DNA polymerases synthesize DNA with a very low error rate and have mechanisms to repair their errors, alterations do occasionally occur. These changes produced in DNA replication are mutations.

Hugo de Vries, in addition to being one of those who rediscovered Mendel's laws in 1900, was the first to use the term mutation when studying the sudden changes that appeared in the offspring of some Oenothera lamarkiana plantsHe defined mutation as "any heritable change in hereditary material that cannot be explained by segregation or recombination."

This definition changed when it became known that the hereditary material is DNA and the double helix structure of DNA (Watson and Crick, 1953). Mutation was defined as any change in the nucleotide sequence of DNA.

The DNA changes also involve changes in the sequence of amino acids constituting the protein corresponding, so that mutations can affect survival of the organism.

Mutations can be classified according to several criteria:

  • According to the type of cells that are affected:
    • Somatic: They are not inherited, since they are only transmitted to cells that originate from mitosis. They are the majority.
    • Germ: They affect the gametes or the cells that produce them, and are transmitted to the offspring.
  • According to the cause that originated them:
    • Natural or spontaneous.
    • Induced by mutagens. The causes of these mutations will be discussed in another section.
  • According to the effects it produces in the body:
    • Beneficial. Some mutations (less than 1%) improve the function of the protein they encode.
    • Harmful or deleterious.
    • Neutral. They are silent, they neither benefit nor harm.

Jonsta247 [GFDL or CC BY-SA 4.0-3.0-2.5-2.0-1.0], via Wikimedia Commons

    • Although the mutation is passed on to the offspring, sometimes it may not manifest itself. If it is a dominant character, it can be easily appreciated, but if it is recessive, it is difficult to detect it, since it only manifests itself if the individual is homozygous recessive.

      The mutation, along with the meiotic recombination, is the source of genetic variability that enables evolution

      Although there are only approximately 10-5 mutations per gene and generation, in a diploid organism such as humans, with about 105 genes, the mutations that each individual has at birth are 10-5 * 105 * 2 = 2 mutations, which is a considerable amount.

    Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

    Aragon. September 2018, option A, question 4. September 2014, option B, question 1.

    Mutations (2.5 points)

    a) Concept (0.5 points)

    Aragon. June 2013, option B. Issue 4.

    Reasonedly answer the following questions: (1 point)

    a) After a hypothetical nuclear accident, the inhabitants of a nearby town were examined. It was observed that his genotype had suffered some alterations. Will their descendants inherit these alterations? Give reasons for your answer.

    b) In this second hypothetical case, a spectacular fire broke out in a chemical industry that affected thousands of people causing severe skin burns. However, the descendants of these affected people were born without any disorder. Explain the reason.

    Aragon. June 2012, option B, question 4 .

    a) Could a population of genotypically identical organisms that reproduce asexually evolve if no mutations occurred? Reason for the answer. (0.5 points)

    b) A fire has produced large changes in the phenotype, although not in the genotype, of individuals in a population of mice. Will those changes be inherited by descendants? (0.2 points) A chemical agent has produced changes in the genotype, although not in the phenotype, of the individuals in a population. Will those changes be inherited by descendants? (0.3 points). Reason for the answers.

    Aragon. June 2009, option A. 4 . (2 points): June 2005, option B. Question 4 . - (2 points)

    a) What are mutations?

    b) Example of each one of the types that you know.

    c) What biological significance do they have?

    d) Is it possible that a single base change from a gene results in the same protein?

    e) Is it possible that the change of a single base produces an identical protein, but much shorter?

    f) Can a change in one base give rise to a totally different protein?

    Navarra, July 2021, question 13

    What is a mutation? What difference does it make if a mutation occurs in a somatic cell or if it occurs in a germ cell?

    Fundamental ideas about mutations

    The mutations are changes that occur in the random DNA.

    • If the mutation occurs in a somatic cell, the mutation will affect only the individual who has it, without being passed on to their descendants.
    • If the mutation occurs in a germ cell, whose function is to join another germ cell to generate a new generation of individuals, it will be transmitted to the descendants.


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