Genetic polymorphism is a condition in which there is a long-term diversity of genes, but the frequency of the most rare gene in the population is more than one percent. Its maintenance occurs due to the constant mutation of genes, as well as their constant recombination. According to studies conducted by scientists, genetic polymorphism is widespread, because there can be several million combinations of a gene.
Large Stock
The better adaptation of a population to a new environment depends on a large stock of polymorphism, and in this case, evolution occurs much faster. There is no practical possibility to evaluate the entire number of polymorphic alleles using traditional genetic methods. This is due to the fact that the presence of a certain gene in the genotype is carried out by crossing individuals that have different phenotypic features determined by the gene. If you know what part of a certain population is made up of individuals withdifferent phenotype, it becomes possible to establish the number of alleles on which the formation of a particular trait depends.
How did it all start?
Genetics began to develop rapidly in the 60s of the last century, it was then that protein or enzyme gel electrophoresis began to be used, which made it possible to determine genetic polymorphism. What is this method? It is with the help of it that the movement of proteins is caused in an electric field, which depends on the size of the moved protein, its configuration, as well as the total charge in different parts of the gel. After that, depending on the location and number of spots that appeared, the identified substance is identified. To assess protein polymorphism in a population, it is worth examining approximately 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 research, some genes can be monomorphic, while others can be 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 puts pressure on the population. In addition, it can be genetic and chromosomal.
Gene and chromosome polymorphism
Gene polymorphism is represented in the body by more than one allele, a striking example of this can be blood. Chromosomalrepresents differences within chromosomes that occurs due to aberrations. At the same time, there are differences in heterochromatic regions. In the absence of a pathology that will lead to a violation or death, such mutations are neutral.
Transient polymorphism
Transitional polymorphism occurs when an allele that was once common is replaced in a population by another that provides its carrier with greater adaptability (also called multiple allelism). With this variety, there is a directed shift in the percentage of genotypes, due to which evolution occurs, and its dynamics is carried out. The phenomenon of the industrial mechanism can be a good example that characterizes transitional polymorphism. What it is is shown by a simple butterfly, which, with the development of industry, changed the white color of its wings to dark. This phenomenon began to be observed in England, where more than 80 species of birch moth moths turned dark from pale cream flowers, which was first noticed after 1848 in Manchester in connection with the rapid development of industry. Already in 1895, more than 95% of the moths acquired a dark wing color. Such changes are connected with the fact that tree trunks have become more smoked, and light butterflies have become easy prey for thrushes and robins. Changes occurred due to mutant melanistic alleles.
Balanced polymorphism
Definition"polymorphism balanced" characterizes the absence of a shift in any numerical ratios of various forms of genotypes in a population that is in stable environmental conditions. This means that from generation to generation the ratio remains the same, but may fluctuate slightly within one or another value, which is constant. Compared to transient, balanced polymorphism - what is it? It is primarily a static evolutionary process. I. I. Schmalhausen in 1940 also gave it the name of an equilibrium heteromorphism.
An example of balanced polymorphism
A good example of balanced polymorphism is the presence of two sexes in many monogamous animals. This is due to the fact that they have equivalent selective advantages. Their ratio within one population is always equal. If there is polygamy in the population, the selective ratio of representatives of both sexes can be violated, in which case representatives of one sex can either be completely destroyed or eliminated from reproduction to a greater extent than representatives of the opposite sex.
Another example would be the blood type according to the AB0 system. In this case, the frequency of different genotypes in different populations may be different, but along with this, from generation to generation, it does not change its constancy. Simply put, no one genotype has a selective advantage over another. According to statistics, men with the first blood group havegreater life expectancy than the rest of the stronger sex with other blood types. On a par with this, the risk of developing duodenal ulcer in the presence of the first group is higher, but it can perforate, and this will cause death in case of late assistance.
Genetic balance
This fragile state can be violated in the population as a result of spontaneous mutations, while they must be with a certain frequency and in each generation. Studies have shown that polymorphisms of the genes of the hemostasis system, the decoding of which makes it clear whether 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 comes down to 0. Mutations of this kind are swept aside in the process of natural selection, but this does not exclude the repeated change of the same gene that compensates for the elimination that is carried out by selection. Then equilibrium is reached, mutated genes can appear or, conversely, disappear. This results in a balanced process.
An example that can vividly characterize what is happening is sickle cell anemia. In this casethe dominant mutated gene in the homozygous state contributes to the early death of the organism. Heterozygous organisms survive but are more susceptible to malaria. The balanced polymorphism of the sickle cell anemia gene can be traced in the areas of distribution of this tropical disease. In such a population, homozygotes (individuals with the same genes) are eliminated, along with this, selection in favor of heterozygotes (individuals with different genes) operates. Due to the ongoing multi-vector selection in the gene pool of the population, genotypes are maintained in each generation, which provide better adaptability of the organism to environmental conditions. Along with the presence of the sickle cell anemia gene in the human population, there are other types of genes that characterize polymorphism. What does it 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 along with this, they can accumulate in the population to a high level, which can exceed harmful dominant mutations.
A sine qua non of the evolutionary process
The evolutionary process is continuous, and its obligatory condition is polymorphism. What it is - shows the constant adaptability of a particular population to its environment. Diverse organisms that live within the same group can be in a heterozygous state and be transmitted from generation to generation forfor many years. Along with this, they may not have a phenotypic manifestation - due to the huge reserve of genetic variability.
Fibrinogen gene
In most cases, researchers consider fibrinogen gene polymorphism as a precursor to the development of ischemic stroke. But at the moment, the problem is coming to the fore, 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 arteries of the brain, and by studying the polymorphism of the fibrinogen gene, one can understand many processes, influencing which, the disease can be prevented. The relationship between genetic changes and biochemical parameters of blood is currently 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.
