The term “mutation” was proposed by the Dutch scientist G. de Vries in 1901.
Mutations are abrupt, persistent, sudden changes in genetic material that are inherited.
Properties of mutations:
- come on suddenly;
- are inherited;
- have no directional character, they cannot be predicted;
- can be beneficial or harmful to the body;
- similar mutations can occur repeatedly.
Causes of mutations
Mutations occur constantly in all living organisms under the influence of mutagenic factors.
Mutagenic factors are factors of the external and internal environment that can cause mutations.
Physical factors include ionizing radiation, ultraviolet radiation, and elevated temperatures. Under their influence, DNA molecules are damaged, which leads to the appearance of mutations.
Chemical factors are substances that change the hereditary material. Mutagenic action was found in formaldehyde, colchicine, lead and mercury compounds, some pesticides, components of tobacco smoke, etc.
Biological factors are living organisms. It has been established that viruses and mold toxins have a mutagenic effect.
Classification of mutations
1. Distinguish between spontaneous and induced mutations.
Spontaneous mutations occur under the influence of natural mutagenic environmental factors without human intervention. They increase the diversity of living organisms and create material for natural selection.
Induced mutations occur when mutagenic factors are targeted at the body. The use of mutagenic effects makes it possible to increase the number of mutations by hundreds of times. Thus, the use of chemical mutagens by breeders made it possible to obtain polyploid forms of plants, which are distinguished by resistance to adverse conditions and higher productivity.
2. Mutations can occur in somatic or germ cells.
Somatic mutations occur in any cell other than gametes. They affect part of the body (for example, different color of petals in one flower, different color of eyes in humans and animals).
Such mutations are not inherited during sexual reproduction, but are transmitted during vegetative reproduction. They are widely used in plant breeding for the development of new varieties.
Generative mutations occur in primary germ cells or in gametes, are inherited during sexual reproduction (for example, hemophilia, Down syndrome in humans).
3. According to the effect on the viability of individuals, the following types of mutations are distinguished:
- lethal (lead to the death of mutants);
- semi-lethal (reduce the viability of the organism, cause hereditary diseases, shorten life expectancy);
- neutral (change the trait, but do not affect the viability of the organism);
- useful (increase the vitality of the body).
4. Mutations are dominant and recessive.
Dominant mutations appear immediately and are subjected to the action of natural selection (useful ones are preserved, harmful ones are removed).
Most mutations are recessive, and they can only appear in a homozygous state. The probability of such an event is small; therefore, recessive mutations accumulate in the population in a latent form for a long time.