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 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 gene combinations can be several million.
Large stock
The best adaptation of the population to a new habitat depends on a large supply of polymorphism, and in this case, evolution occurs much faster. To evaluate 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 carried out by crossing individuals that have different phenotypic characteristics determined by the gene. If you know what part in a certain population are individuals with a different phenotype, then it becomes possible to establish the number of alleles on which the formation of a particular trait depends.
How it all began?
Genetics began to develop rapidly in the 60s of the last century, it was then that electrophoresis of proteins or enzymes in a gel began, which made it possible to determine genetic polymorphism. What is this method? It is with the help of it that the movement of proteins in the electric field is caused, which depends on the size of the transferred protein, its configuration, as well as the total charge in different parts of the gel. After that, depending on the location and the number of spots that have appeared, identification of the identified substance is carried out. To evaluate 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 gene and chromosomal.
Gene and chromosomal polymorphism
Gene polymorphism is represented in the body by alleles in an amount of more than one, blood can become a vivid example of this. Chromosomal represents the differences within the chromosomes, which occurs due to aberrations. Moreover, there are differences in heterochromatin regions. In the absence of pathology that will lead to disruption or death, such mutations are neutral in nature.
Transient polymorphism
Transitional polymorphism occurs when an allele that was once common in the population is replaced by another that provides its carrier with greater adaptability (this is also called multiple allelism). With this variety, there is a directed shift in the percentage of genotypes, due to it, evolution occurs, and its dynamics are carried out. The phenomenon of the industrial mechanism can be a good example that characterizes the transitional polymorphism. What it is, shows a simple butterfly, which with the development of industry has changed the white color of its wings to dark. This phenomenon began to be observed in England, where more than 80 species of butterflies of
birch moths from pale cream flowers became dark, 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 color of the wings. Such changes are connected with the fact that tree trunks have become more sooty, and light butterflies have become easy prey for thrushes and robins. Changes occurred due to mutant melanistic alleles.
Balanced polymorphism
The definition of "balanced polymorphism" 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 can fluctuate slightly within a given value, which is constant. Compared to transitional, balanced polymorphism - what is it? It is primarily the static of the evolutionary process. I. I. Schmalhausen in 1940 also gave him the name equilibrium heteromorphism.
An example of balanced polymorphism
A good 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. Their ratio within the same population is always equal. In the presence of polygamy in the population, the selective ratio of representatives of both sexes can be violated, in this case, 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 affiliation of blood according to the AB0 system. In this case, the frequency of different genotypes in different populations may be different, but along with this, it does not change its constancy from generation to generation. Simply put, no genotype has a selective advantage over another. According to statistics, men with the first blood group have a longer life expectancy than other men 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 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
mutations arising
spontaneously, while they must be with a certain frequency and in each generation. Studies have shown that polymorphisms of the genes of the hemostatic system, the decoding of which makes it clear that the evolutionary process contributes to these changes or, conversely, counteracts, are extremely important. If we trace the course of the mutant process in a given population, then we can also judge its value for adaptation. It can be equal to unity if the mutation is not excluded in the selection process, and there are no obstacles to its spread.
Most cases show that the value of such genes is less than unity, and in the case of the inability of such mutants to reproduce, it all comes down to 0. Mutations of this kind are eliminated in the process of natural selection, but this does not exclude the repeated change of the same gene, which compensates for elimination which is carried out by selection. Then equilibrium is reached, mutated genes can appear or, conversely, disappear. This leads to a balanced process.
An example that can vividly characterize what is happening is sickle cell anemia. In this case, the dominant mutated gene in a homozygous state contributes to the early death of the body. Heterozygous organisms survive, but they are more susceptible to malaria. Balanced polymorphism of the sickle cell anemia gene can be observed at the sites of spread of this tropical disease. In such a population, homozygotes (individuals with identical genes) are eliminated, and selection in favor of heterozygotes (individuals with different genes) is equally valid. Due to the ongoing multi-vector selection in the population’s gene pool, the genotypes are maintained in each generation, which provide better adaptability of the organism to the environment. Along with the presence of the sickle cell anemia gene in the human population, there are other varieties 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.
An indispensable condition for the evolutionary process
The evolutionary process is continuous, and its prerequisite is polymorphism. What is it - shows the constant adaptability of a population to their environment. Homosexual organisms that live within the same group can be in a heterozygous state and transmitted from generation to generation for many years. Along with this, their phenotypic manifestations may not exist - due to the huge stock of genetic variation.
Fibrinogen gene
In most cases, researchers consider fibrinogen gene polymorphism as a prior condition for 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, you can understand many processes, affecting which, the disease can be prevented. The relationship of genetic changes and biochemical blood parameters at the moment, scientists are not well understood. Further research will allow you to influence the course of the disease, change its course or simply prevent it at an early stage of development.