Polymorphism - what is it? Genetic polymorphism

Genetic polymorphism is a condition in which a prolonged variety of genes is observed, but the frequency of the most rare gene in the population is more than one percent. Its maintenance is due to the constant mutation of genes, as well as their constant recombination. According to studies conducted by scientists, genetic polymorphism has become widespread, because the gene combinations may be several million.

Large inventory

From a large margin of polymorphism, the best adaptation of the population to a new habitat depends, and in this case evolution occurs much faster. Estimate the total number of polymorphic alleles, using traditional genetic methods, there is no practical possibility. This is due to the fact that the presence of a specific gene in the genotype is due to the crossing of individuals that have different phenotypic characteristics determined by the genome. If you know what part of a certain population is made up of individuals with different phenotypes, then it becomes possible to establish the number of alleles on which the formation of a particular feature depends.

How it all began?

Genetics began to develop rapidly in the 60s of the last century, when electrophoresis of proteins or enzymes in the gel began to be used, which made it possible to determine genetic polymorphism. What is this method? It is through him that the movement of proteins in the electric field is caused, which depends on the size of the protein being transported, its configuration, and also the total charge in different parts of the gel. After this, depending on the location and number of spots that appeared, identification of the determined substance is carried out. To evaluate protein polymorphism in a population, it is worth exploring about 20 or more loci. Then, using the mathematical method, the number of allelic genes is determined , as well as the ratio of homo- and heterozygotes. According to studies, some genes can be monomorphic, and others - unusually polymorphic.

Types of polymorphism

The concept of polymorphism is extremely broad, it includes a transitional and balanced version. It depends on the selective value of the gene and natural selection, which presses on the population. In addition, it can be genomic and chromosomal.

Genomic and chromosomal polymorphism

The gene polymorphism is represented in the body by alleles in the amount of more than one, a clear example of this can be blood. Chromosomal is the difference within the chromosomes, which occurs due to aberrations. There are differences in heterochromatic sections. In the absence of a pathology that leads to disruption or death, such mutations are neutral.

Transitional polymorphism

Transient polymorphism occurs when the population replaces an allele that was once common, another that provides its carrier with greater adaptability (this is also called multiple allelicism). With this variety there is a directed shift in the percentage of genotypes, due to it, evolution occurs, and its dynamics is realized. The phenomenon of the industrial mechanism can be a good example, which characterizes the transitional polymorphism. What it is, shows a simple butterfly, which, with the development of industry, changed the white color of its wings to a dark one. This phenomenon began to be observed in England, where more than 80 species of butterfly moths made of pale cream-colored flowers became dark, which was first noticed after 1848 in Manchester due to the rapid development of industry. Already in 1895 more than 95% of moths acquired a dark color of wings. Such changes are connected with the fact that tree trunks have become more sooty, and light butterflies have become an easy prey for blackbirds and ruffians. Changes occurred due to mutant melanistic alleles.

Balanced polymorphism

The definition of "balanced polymorphism" characterizes the absence of a shift in any numerical relationships of different forms of genotypes in a population that is in stable habitat conditions. This means that, from generation to generation, the ratio remains the same, but it can vary slightly within a particular quantity that is constant. In comparison with transient, balanced polymorphism - what is it? First of all, it is a static of the evolutionary process. II Shmalhausen in 1940 also gave him the name of equilibrium heteromorphism.

An example of a balanced polymorphism

A clear example of balanced polymorphism can be the presence of two sexes in many monogamous animals. This is due to the fact that they have equivalent selective advantages. The ratio of them within the same population is always the same. In the presence of polygamy in the population, the selective ratio of the representatives of both sexes can be violated, in which case the representatives of the same sex can either be completely destroyed or eliminated from reproduction to a greater extent than representatives of the opposite sex.

Another example is the group membership of blood in the ABO system. In this case, the frequency of different genotypes in different populations may be different, but on a par with that from generation to generation it does not change its permanence. Simply put, no genotype has a selective advantage over the other. According to statistics, men who have the first blood group have a greater expected life expectancy than the rest of the stronger sex with other blood groups. Along with this, the risk of developing duodenal ulcer in the presence of the first group is higher, but it can be perforated, and this will cause death in case of late assistance.

Genetic balance

This fragile state can be violated in the population as a consequence of spontaneously occurring mutations, but they must be with a certain frequency and in each generation. Studies have shown that polymorphisms of genes of the hemostasis system, the interpretation of which makes it clear, the evolutionary process contributes to these changes, or, conversely, counteracts, are extremely important. If we trace the course of the mutant process in a particular population, we can also judge its value for adaptation. It can be equal to one if the mutation is not excluded during the selection process, and there are no obstacles to its spread.

Most cases show that the value of such genes is less than one, and in the case of the inability of such mutants to reproduce, everything is reduced to 0. Mutations of this kind are discarded in the course of natural selection, but this does not exclude repeated changes of the same gene, which compensates for elimination , Which is carried out by selection. Then equilibrium is achieved, mutated genes can appear or, conversely, disappear. This leads to a balanced process.

An example that can clearly describe what is happening is sickle-cell anemia. In this case, the dominant mutated gene in the homozygous state contributes to the early death of the organism. Heterozygous organisms survive, but they are more susceptible to malaria. Balanced polymorphism of the sickle-cell anemia gene can be traced in the areas of this tropical disease. In such a population homozygotes (individuals with the same genes) are eliminated, along with this selection works in favor of heterozygotes (individuals with different genes). Due to the ongoing multi-vector selection in the gene pool of the population, genotypes are maintained in each generation, which ensure the best adaptability of the organism to the conditions of the habitat. Along with the presence of the gene of sickle-cell anemia in the human population, there are other varieties of genes that characterize polymorphism. What does this give? The answer to this question will be such a phenomenon as heterosis.

Heterozygous mutations and polymorphism

Heterozygous polymorphism provides for the absence of phenotypic changes in the presence of recessive mutations, even if they are harmful. But on a par with this, they can accumulate in the population to a high level, which can exceed harmful dominant mutations.

The indispensable condition of the evolutionary process

The evolutionary process is continuous, and its obligatory condition is polymorphism. What this - shows the constant adaptability of a particular population to its habitat. The heterozygous organisms that live within the same group may be heterozygous and transmitted from generation to generation for many years. Along with this phenotypic manifestation, they may not be - due to the huge stock of genetic variability.

The gene of fibrinogen

In most cases, researchers consider the polymorphism of the fibrinogen gene as a precursor to the development of ischemic stroke. But at the moment, the problem is at the forefront, in which genetic and acquired factors are able to exert their influence on the development of this disease. This type of stroke develops due to thrombosis of the cerebral arteries, and, by studying the polymorphism of the fibrinogen gene, many processes can be understood, influencing which the ailment can be prevented. The connections of genetic changes and biochemical indicators of blood at the moment are insufficiently studied by scientists. Further research will allow to influence the course of the disease, change its course or simply prevent it at an early stage of development.