People from the very beginning of their existence are engaged in the knowledge of themselves and the world. And often, research activity leads to the fact that people deliberately interfere in the usual processes, thereby disrupting the course of events and introducing obvious changes that affect not only the surrounding nature, but also on the person.
Definition
Mutagenesis is a process of changes in the structure of DNA, resulting in a mutation of the body.
Two types of mutagenesis are distinguished: artificial (induced) and natural (spontaneous).
Discovery history
In 1899, the Russian scientist Korzhinsky provided a scientific explanation of mutagenesis. In 1900, the geneticist Frieze continued to study the phenomenon, and it was this scientist who gave the current definition of mutagenesis.
These two scientists derived the following provisions of his theory:
- All mutation processes are sudden, like intermittent changes in traits.
- The new forms obtained are stable.
- Mutations do not “build” successive series, do not accumulate near the middle type. This significantly distinguishes mutational changes from hereditary ones.
- Similar mutations may occur periodically.
- Depending on the number of individuals studied, the likelihood of detecting a mutation increases.
- Mutations are both harmful and beneficial.
Why mutations appear
Most often, mutagenesis occurs when mistakes are made during doubling and restoration of DNA chains, when there is a violation in the divergence of chromosomes to the poles during meiosis.
In general, in every cell there is a constant restoration of broken DNA chains. However, if DNA integrity is not restored, then all errors in the genetic code will accumulate, which will ultimately lead to a mutation process.
Spontaneous mutagenesis
It occurs under natural conditions of development, when no mutagens act from the outside.
What could be the reasons for the appearance of such a species:
- Exogenous (or external): radiation, extremely low or high temperatures.
- Endogenous (or internal). These include metabolites that suddenly form in the body, which arouse the formation of mutational processes.
For example, in areas of arctic cold vegetation has a polyploid shape. This depends on the fact that during the growing season at abnormally low temperatures, a number of genomic mutations are formed in plants.
For a long time, scientists believed that the factors of the occurrence of natural mutagenesis are cosmic waves and natural radiation. However, in the course of the studies it was found that only a small fraction of spontaneous mutagenesis is formed under the influence of radiation.
It is established that the cause is local small deviations of the thermal motion of particles.
Induced
Artificial mutagenesis is the process of creating artificial mutations to produce the necessary material.
For example, in plant breeding, scientists use mutagenic factors that transform the original genotype. In the course of this, modified plant species are obtained with new traits and forms that are not present in their original species.
Therefore, we can say that induced mutagenesis in breeding plays an important role in obtaining new varieties.
Spontaneous Type Mutagenesis
Its mechanism looks like a violation of a DNA fragment. If it was carried out with errors, then the formation of a mutation is inevitable. If the violation occurred in an unimportant part of the DNA, or vice versa, in a significant fragment, the mutation will appear, but will not appear once and more.
Mutagens: physical and chemical
Mutagens are phenomena that cause mutational changes in the body. By the nature of their origin, they are all divided into physical and chemical.
Physical mutagens include:
- Ionizing radiation.
- Temperature.
- Humidity.
The methods of exposure are as follows:
- Destruction of the integral structure of chromosomes and genes.
- The release of free-type radicals that begin to interact with DNA.
- Violation of the integrity of the chromatin spindle threads.
- The emergence of dimers - the formation of single complexes of pyrimidine bases of one DNA chain.
Chemical mutagens are as follows:
- Chemicals of organic and inorganic nature.
- Substances of a synthetic nature that have not been found in nature before.
- Natural substances after factory processing, such as coal and oil.
- Some medicines, drugs, some types of antibiotics.
The mechanism of chemical mutagens is as follows:
- Alkylation of nucleotide DNA complexes.
- Substitution of nitrogenous bases with bases of a similar nature.
- Slowing down the synthesis of nucleic acid precursors.
Is mutagenesis useful?
So, we can say with confidence that mutagenesis is a phenomenon that can affect the state of the body.
If a mutagen affects a “minor” DNA fragment, then, in fact, the body will not undergo any changes. Mutations will exist in the "memory" of DNA and be inherited, and over time they may disappear altogether.
But if mutagenesis factors affect a substantial DNA fragment, as a result of which the standard amino acid sequence is disrupted, then this will lead to irreversible changes in the body. And if the mutation is detected in the vast majority of individuals of a certain species, then in the future this will lead to significant changes in the characteristic features of the species.
Since mutagenesis is a violation of the normal integrity of DNA, mutations can harm the body.
The vast majority of mutations can reduce the vital activity of organisms and provoke the appearance of serious diseases.
Those consequences of mutagenesis that are formed in somatic cells are not transmitted with the genetic material to the next generation. But as a result of mitotic division, when new cells that form the tissue appear, tumor seals can form.
Mutations that affect germ cells can be passed on to the next generation.
A specific example: a mutation leading to the appearance of shortened wings in one of the representatives of the insect will subsequently manifest itself in the rest of its species, and if these insects live in a calm region, then it will be difficult for them to move. In this case, we will be talking about an acquired disease or even ugliness.
But if strong winds begin to blow in such an area, then the initial appearance of insects with long wings will inconvenience, and short-winged, on the contrary, will have advantages.
Thus, we can say that mutations can give rise to a new species of organisms by changing the genomic structure of an existing species.