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11.4. Evolutionary implications of mutations

Mutations and evolution

The mutations have occurred over time, by causes natural as radiation from the sun or minerals from the earth's crust. Although they are not very frequent, since they cover very large periods of time and very large populations, the probability that a mutation will appear is considerable.

Most are lethal and disappear with their carriers, but when they are beneficial they remain in the individuals of the population and are transmitted to their offspring. If natural selection acts on these genotypesand they are favorable to those environmental conditions, it can even become incorporated as a  singlehomozygouscharacter, making the old normal character of the population disappear. If the mutation is harmful, if they are recessive, they will remain in the population.

If the mutation is beneficial, it can improve the function of the enzyme it encodes, for example, by improving biological activity, facilitating the life of the organism that carries that mutation.

Neutral mutations neither improve nor harm the conditions of the individual who is the carrier of the mutated gene, but can be passed on to descendants. It can serve as a biological clock to know how long two species have separated since they had a common ancestor.

All cells can suffer some mutation, but the mutations that affect the gametes will affect the zygote that is formed after fertilization with another gamete and the cells that derive from it to form the new multicellular being. In addition, he will transmit the mutation to his descendants. Therefore, beneficial germline mutations will be those that cause the  evolution of the species. The individual carrying the mutation has an advantage over those who do not have it, so they will be more likely to have offspring and transmit this advantageous characteristic to their descendants.

Harmful mutations only remain in the population when they are recessive. If the mutation occurs in a somatic (non-germ) cell, it will not be passed on to offspring.

When mutations appear in a certain population, the genotype changes from generation to generation, appearing individuals with characteristics different from those of their predecessors. This is how the population evolves , being able to originate new species. An example is bacteria that evolve after being subjected to antibiotics, becoming resistant.

Mutations that are detrimental to the carrier individual will be eliminated by natural selection.

In addition to natural selection, man has made artificial selection on domestic plants and animals, modifying them according to his own interest. It has achieved this by selecting the most productive individuals and crossing them with each other, obtaining different breeds, as in the dog, for example.

The evolution occurs because people change their "pool" gene, the set of genes formed by all allelesexist among individuals. If an individual has the most favorable alleles, he has an advantage over the rest, being able to survive more easily. Thus, it is more likely that it is reproduced and that thesegenes remain in the population.

Although mutation is the primary source of variation, it is not the only one. Thegene recombination  contributes to thevariability gene in sexually reproducing organisms.

The evolution of species occurs because the changes produced by genetic mutations accumulate. Most mutations are harmful and their carriers die, but those that produce an improvement remain in the species and are essential in the evolutionary process.

When there is a separation between some members of a population, their genetic exchange is interrupted. Being in different environments, this differentiation is becoming more and more noticeable. With the passage of time, their genetic differences will be so great that they will have become different species, being unable to reproduce among them.

Factors involved in biological evolution

The gene pool of a population is made up of all the alleles of the individuals in the population. For evolution to occur, there must be genetic variability among individuals in a population, and that genetic variety can be inherited by future generations.

The factors that produce alterations in the gene and genotypic frequencies of certain alleles and, therefore, in the composition of the genes that make up the population are:

Natural selection

The natural selection acts when the selected environment those individuals best adapted to these environmental conditions. Those with those genes that are best adapted to the changes that take place will be the ones that will have the easiest survival and reproduction, and can pass these genes on to their descendants.

Mutations

The mutations  occur when, due to an error in the process ofreplication of DNA, there are changes in the sequence of nucleotides of the DNAand new alleles are generated. Mutations are random and are the main cause of genetic variability. The only heritable mutations are those that affect the gametes and can be harmful, neutral, or beneficial.

Crossover and genetic recombination

Gametes are produced through meiosis. In Prophase Igenetic crossover and recombination occurs between paternal and maternal genes , favoring variability. Furthermore, the randomness in the union of gametes further increases the variability.

Genetic drift

The genetic drift is the random fluctuation of the allelic frequencies occurs generation after generation. The effects of genetic drift are strongest in small populations, where genetic variability decreases markedly. For instance:

  • Founder effect: when some individuals of a population are isolated from the original population they reproduce and transmit their alleles to their descendants. Possibly, the gene frequencies of that group are not the same as those of the original population. For example, the Amish, a group that only had 12 founders of which only one had a gene that caused the combination of dwarfism and polydactyly, and at present, that allele is carried by 13% of the population of that group.
  • Bottleneck effect: when there is a sharp decrease in the number of individuals in a population, due to some type of natural or human disaster, the individuals that survive have different allelic frequencies than the original population.

Migrations or gene flow

The migratory flows make the population acquires greater genetic variability, as new alleles from other populations, are incorporated into the gene pool of the population.

Reproductive or genetic isolation

When a population or group of individuals in a population is reproductively isolated from the rest of the individuals by barriers that prevent it, such as differences in behavior, habitats, etc., the speciation process can take place and a new species can emerge.

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)

d) Relationship of mutations with evolution. (0.75 points)

Aragon. June 2016, option B, question 4.

Mutations: (2 points)

c) Are mutations random or directed toward a specific change? Reason for the answer. (0.5 points)

d) Why are mutations the basis of selection in species? (0.5 points)

Aragon. September 2015, option B, question 4.

Mutations (2 points)

b) Indicate the meaning of the mutations from the evolutionary point of view. (0.5 points)

Aragon.  June 2010, option A. 4 .

About the processes of mutation and evolution: (2 points)

a) What is biological evolution?

b) What is the cause of genetic variability in organisms with asexual reproduction?

c) What is the cause of genetic variability in organisms with sexual reproduction?

Aragon. June 2007, option A. Question 4 .- (1 point).

Explain the implications of mutations in the evolution of living things.