| Mutation – genotype changes, occurring under the influence of external or internal factors. The occurrence process of mutation received the name “Mutagenesis”.
The natural rate of the occurrence of mutation is often much less, because, usually mutation takes place in one cell and affects one gene. The majority of these mutations are absolutely safe, because they do not completely affect the phenotype. A relatively small fraction of mutations cause changes in the RNA structure and-or proteins and then there is a chance of mutation affecting the functionality of cells. Mutations, which worsen the activity of cells in metazoan organism, often lead to cell destruction. If the inner and outer cell protective mechanisms did not distinguish the mutation, then the mutant gene is transmitted to all descendants of the cells and, more often, leads to the malfunctioning of cells. Mutations take place constantly during the processes, occurring in a live cell, but there exists factors, capable of significantly increasing the frequency of mutations. The most widespread of them is the influence of harmful substances, microorganisms or radiation including the natural radiating background on cells.
Mutation in the somatic cell of the complex metazoan organism can lead to malignant or benign new formations. The mutation in sexual cells leads to changes in the characteristics of the entire descendant organism.
Most cases of mutations, which appear at the phenotype level, have fatal consequences and the mutant organism perishes by itself or under the influence of the environment. However, in very rare cases, mutation can casually lead to the occurrence of new useful features in the organism and then the consequences of mutation appear positive. Thus, mutations are engines of natural selection.
Also it is known that the higher organisms use purposeful mutations in immunity mechanisms. Such mutations are called “somatic”. With their help, a variety of lymphocyte populations are created, among which, as a result, units are found always, which are capable of giving an immune response to a new, unknown illness of the organism. Suitable lymphocytes are subjected to positive selection and immunological memory appears as a result.
If the mutation affects “silent” sections of DNA or leads to the replacement of one element of genetic code, then it is not shown in any way outwardly in the phenotype. However, such mutations can be detected through gene analysis methods. Since mutations occur more often as a result of natural reasons, then in assumption, that basic properties of external factors did not vary, turns out, that the frequency of mutations should be approximately constant. This fact can be used for the research of origin of anything including the human being. Thus, mutations in silent genes give researchers unique “genetic clocks”.
Spontaneous DNA damage is encountered very often and such events take place in each cell. Special reparation mechanism (for example, the mistaken section of DNA is cut and the original section is restored at the same place) is available for rectifying the consequences of similar damage. Mutations arise only when the reparation mechanism, for any reasons, does not work or does not cope with the rectification of damage.
Research of mutations in mitochondrial DNA (inherited from the maternal line) and in Y-chromosomes (inherited from paternal line) is widely used in evolutionary biology for studying the origin of races and nationalities and the reconstruction of biological development of mankind. |
February 12th marked the 200th birthday for famous evolution scientist Charles Darwin, who laid the foundations for the evolution theory - mutation & natural selection. As per Darwin, mutation provides new traits for species, and then the nature "selects" those species with advantageous heritable traits - the process Darwin called "natural selection".
