Under the action of elementary factors in the gene poolthe frequency of certain genes changes, which leads to a change in the genotype and in the phenotype of the population, and with prolonged exposure to natural selection, its differentiation passes.
Microevolution - changes in the population under the influence of evolutionary factors, which can lead to changes in the gene pool or even the emergence of a new species.
Factors of evolution can be called any processes or phenomena. Among them should be called mutations, isolation, gene drift, population waves, which change the genetic composition.
These waves are characteristic of all living organisms.They can be periodic and non-periodic. Periodic ones are most often observed in short-lived organisms — in insects, annual plants, and also in most microorganisms and fungi. The simplest example would be seasonal changes in abundance.
Non-periodic population waves depend oncombinations of several complex factors. As a rule, they concern not one, but several types of living organisms in a biogeocenosis, therefore they can lead to radical reorganizations.
Among the changes in the number of individuals in the populationIt is necessary to single out the sudden appearance of certain types of organisms in new areas where their natural enemies are absent. We should also mention abrupt non-cyclical changes in abundance, which are associated with natural “catastrophes” and can be manifested by the destruction of the biogeocenosis or the whole landscape. So, a few dry summer periods can change a significant area - to cause the appearance of meadow vegetation in swamps and a large number of dry meadows.
In cases where the number of any populationdecreases sharply, there may be only a few individuals. At the same time, their frequency of genes (alleles) is different from the one that was in the original population. If, after a sharp decline in the population, there is a sharp rise in the population, then the beginning of a new outbreak of growth in the number of individuals in the population is provided by a small group of organisms that remain. That is why it can be argued that population waves affect the gene pool, since the genotype of this group determines the genetic structure of the entire population.
In this case, quite by chance it changes dramaticallya set of mutations in the population and their concentration. So, a certain part of the mutations disappears altogether, and some suddenly grow. To summarize, it can be said that population waves, as an evolutionary factor, are extremely important, since under the condition of intensive selection they are the main supplier of evolutionary material, when rare mutations are substituted for selection.
In addition, waves of life can temporarilybring a number of mutations or genotypes into another abiotic or biotic environment. Despite this, even the combination of population waves and mutations does not ensure the evolutionary process. You need an action factor, which affects in one direction (this, for example, isolation).
This factor is extremely important in the evolutionaryplan, because it provokes the emergence of new signs in the conditions of one species and does not allow the cross-breeding of different species to take place between them. It is worth noting that geographical isolation is most often observed. Its essence lies in the fact that a single range is broken, while the intersection of individuals from different parts of it becomes impossible or difficult.
Стоит отметить, что в изолированной популяции mutations happen randomly, and as a result of natural selection, its genotype becomes more and more diverse. In addition, there is environmental isolation and various biological mechanisms that prevent individuals of different species from freely converging. An example would be different preferences regarding the place or time of crossing, as well as, for example, the excellent behavior or the different structure of the genital organs in animals, which becomes an additional obstacle to crossing.
To summarize, it can be said that different types of isolation contribute to the formation of new species, but at the same time help to preserve the genetic species structure.
Random change in the number of genes in anysmall populations can have noticeable consequences, since it can lead to a change in the frequency of alleles. Random changes in the frequency of alleles are called gene drift. This process is non-directional. It was first discovered by geneticists N. P. Dubinin and D. D. Romashov.
Confirmation regarding drift randomnessgenes got S. Wright. In the laboratory, he crossed drosophila males and females who were heterozygous for a specific gene. After that, progeny were obtained with a concentration of the normal and mutant gene, which was 50%. After several generations, some individuals became homozygous for the mutant gene, some even lost it, and another part of the individuals had both the mutant and the normal gene.
Следует отметить, что даже при пониженной viability of mutant individuals and subject to the influence of natural selection, the mutant allele was able to completely crowd out the normal one, causing specific population waves.
Of all the reasons that can affectthe quantitative characteristics of the population, the leading place is taken by climatic conditions, biotic factors are thus relegated to the background. With low species diversity, the number of individuals in the population depends on the weather, the chemical composition of the environment, as well as the degree of pollution.
It should be noted that the causes of population waves, which predetermine the change in population size, depend on its density or influence independently of this parameter.
Abiotic and man-made factors likegenerally do not depend on population density. Biotic influence is more dependent on it. It should be noted territorial behavior, which in the course of evolution is the most effective mechanism that inhibits the growth of the number of individuals in the population. Thus, the activity of individuals is limited to the appropriate space. With increasing numbers, intraspecific competition for resources or direct antagonism (attack on competitors) develops.
Many environmental processes associated withthe distribution of the population over the area or with a local outbreak of numbers resembles peculiar waves, which, as mentioned above, are called “waves of life”. A typical example is the sudden increase in the number of insect pests in a limited forest area. Under favorable conditions, insects are capable of capturing more and more new territories, which is a typical picture of an increase in their density or the spread of a so-called population wave. Knowing the characteristics of mobility and certain population characteristics, one can easily calculate the propagation velocity of this wave and possible control methods.
In addition, it is necessary to mention the population-genetic waves, with the help of which they describe the nature of the spread of a particular gene in the area that a particular population occupies.
Population waves can be characterized withusing a model example. So, in the closed box there are 500 black and the same number of white balls, which corresponds to the frequency of the P-0.50 alleles. If you remove 10 balls at random and assume that 4 of them are black and 6 are white, the allele frequency will be 0.40 and 0.60, respectively.
If you increase the number of balls by 100 times,adding 400 black and 600 white, and then again randomly pick up any 10, then it is likely that their color ratio will differ significantly from the original, for example, 2 black and 8 white. The frequency of the alleles will be, respectively, P-0.20 and P-0,80. If we take the third sample, then there is a probability that 9 white balls from 10 chosen ones will be extracted, or even all of them will have a white color.
By this example, it is possible to judge about random fluctuations in the frequency of alleles in natural populations, which can reduce or increase the concentration of a particular gene.
