We are all mutants
The geneticist told about what changes our genome
Mutation of genes, as scientists believe, is the engine of the evolution of all living things. Their cause is errors in the processing of DNA at the cellular level. Konstantin Krutovsky, a geneticist, professor at the Siberian Federal University and the University of Göttingen, told RIA Novosti about how diverse these errors are and how far their consequences stretch.
Mutations occur under the influence of physical and chemical factors – for example, ultraviolet or radioactive radiation – that disrupt the structure of DNA, as well as, according to scientists, as a result of accidental failures in the work of enzymes that play the role of "installers" and "restorers" during the reproduction and restoration of DNA inside a living cell.
New mutants – new species
Genome mutations are the basis of speciation, that is, their accumulation can lead to the formation of a new stable species. According to the expert, this happens especially quickly in the case of genome "closure" within the same population for several generations.
Comparison of the genome of modern man with the genome of his close relatives – Neanderthals or higher primates – shows that the differences in the composition of chromosomes and the number of genes are small. However, the structure of genes and their mutual regulation, according to scientists, is determined by other parameters.
"Cognitive abilities, which largely determine our species uniqueness, are associated with the evolution and mutations of a relatively small number of important genes. Among them are the genes BDNF, DRD2, FNBP1L, PDE1C, PDE4B, PDE4D and a number of others related to the work of brain cells," the expert explained.
Most mutations either do not affect fitness, or affect negatively. Harmful mutations are usually quickly "washed out" from the population, the expert noted. This happens either as a result of natural selection, which cuts off the mutation the faster, the more dangerous it is, or randomly – after all, according to experts, about 20% of people for various reasons do not leave offspring at all.
The independent occurrence of favorable mutations in unrelated populations, according to scientists, confirms that it is natural selection, controlled by environmental factors, that plays a key role in the consolidation of new genes. For humans, an example of this is lactose resistance, developed in different foci of ancient animal husbandry.
Scientists at the German Johann Gutenberg University found out that the ability of people to eat milk in adulthood was the result of a genetic mutation.
The rate of mutations in different species and even in different populations within the same species can vary greatly. The frequency of their occurrence is influenced by many factors – both internal, such as the effectiveness of the body's repair system, and external, such as the degree of environmental pollution by chemical mutagens or radiation.
What do mutations change?
Relatively small mutations – the so–called "dot" - are substitutions, insertions or drops from the DNA chain of individual nucleotides, most of which do not affect survival and fertility.
"As a rule, these are mutations in non-coding regions of a gene or in those positions that do not affect its function, which means they do not cause changes in the products that are encoded by this gene. However, even among these "small" mutations there are harmful ones that cause serious diseases," Konstantin Krutovsky noted.
Neutral mutations include, for example, changes in hair pigmentation or iris. There are mutations that give such ambiguous effects as, for example, the phenomenon of sudden sneezing from bright light or the smell of urine from eating asparagus.
Larger structural mutations are called "chromosomal" because they are associated with the loss or, conversely, the doubling of entire genes or chromosomes. For example, Down syndrome – the most common example of this type of mutation – is the presence of three copies of chromosome 21 instead of the usual two.
Useful mutations happen much less often than others. They are supported by selection and for a number of generations displace other variants of the same gene in the event that the fitness of carriers who received a mutation from both mother and father is higher than that of carriers with or without one copy of the mutation.
An example of a useful mutation is the increased formation of melanin in the population of the equatorial zone. This pigment protects against solar ultraviolet radiation, which can cause skin cancer.
Another option is to increase disease resistance in areas with a high risk of infection. For example, mutations in the gene encoding the beta chain of hemoglobin, which increases the resistance of blood cells to malaria plasmodium – the causative agent of malaria carried by mosquitoes.
Some residents of Italy have a mutation that contributes to the effective removal of "bad" cholesterol from cells, resorption of arterial plaques, and also prevents harm from inflammation in atherosclerosis.
Another example of a useful mutation is a violation of the synthesis of the CCR5 protein, which HIV uses to enter a human cell. Experts believe that such a mutation, which seriously increases resistance to a dangerous virus, will be supported by selection in areas with a high spread of AIDS, even if it has some adverse effects.
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