To make experiments on laboratory animals, it is necessary to know the genotypes of not only certain individuals, but also the genetic structure of the whole line and type. For this purpose, for updating and development biological scienceHer analysis, a special region of genetics was created - population genetics or population genetics. The methods of this science make it possible to open patterns that implement in the aggregate of individuals, that is, in populations.

From a genetic point of view, the population is considered as a combination of individuals of one species inhabiting a certain territory and unequal in their phenotypic and genotypic properties. For analysis, a freely cross, so-called pampamctic population is usually considered as the initial structure of the population and its changes. All the individuals entering it can be paired with each other in any combination, regardless of the genetic structure. Freely crossed populations are possible only in species that breed the sexual way. Research of genetic processes occurring in natural conditions breeding animals, birds, reptiles, insects have great importance For knowledge biological features, specifics of differences and homogeneity in genotype in various media conditions.

In a pamptic population, there is the same probability of a combination of any representatives of the population with each other, as well as equal to the probability of giving offspring, however, it is in mind not to clean the physical pairing of any females with any males, but only the principal possibility of its implementation. It follows the need to build another model, namely: it is possible to consider the entire set of genital cells, which are formed by individuals freely crossing population, as a whole, as if all of them are placed in the vessel and mixed with each other. IN this case The connection of female and male genital cells occurs purely by chance, and its results will depend only on the frequency (or measurable probability frequency) of those or other genital cells. As well as each sex cell to fertilization contains only one gene from a pair or series of alleles, then the combination of genes in the genital cells of all individuals of the population as a single gene pool. The share of certain genes of the same series of alleles is called the frequency of genes.

Depending on the frequencies of individual genes encountered in the population, it is possible to determine the ratio of genotypes and phenotypes. Knowing this ratio can be determined by the frequencies of genes, as the most important parameters for the characteristics of the population.

To parse the generation method of gene frequencies, you can bring specific example. At the experimental rabricifofer, there were 729 rabbits of gray suit (AA), 111 black, which are heterozygous (AA) and 4 bunnies of white (AA). If all categories of individuals are not different from each other in the number of sex cells formed, then, taking for a simple calculation only two genital cells, we obtain the following number of genes A and A in the total gene pool of rabbit-flemes.

Gene A (2a) (729 x 2) + 111 \u003d 1569 genital cells.

AA and AA 111+ (4 + 2) \u003d 119 genital cells.

Total: 1688 genital cells.

By drawing up the ratio: 1688 - 1.0

Treatment: 1688 - 1.0

Total gene amount: p (a) \u003d 0.93

In this simple example The frequencies of genes are calculated based on a known number or shares, genotypically different groups of individuals. Knowing the same gene frequencies can be predicted by specific relations, which will be obtained in the next generation of freely crossing population. Best do it in general For any values \u200b\u200bof P and Q in Genofond. Like females, and males will form gamets of two types A and A in the ratio of p (a): Q (a). The results of the connection of men's and women's weights can be shown using a four-field table 1.

Table 1 - Results of the Connection of Male and Women Games

Men's women		Gamets and their frequencies, ♀
Gamets and their frequencies ♂

In the offspring, three genotypes were formed in the ratio, expressed by the coefficient: R², 2rq and Q² (the sum of the upper and lower fields of the table) or ²aaa + 22pqaa + q²aa.

This ratio of genotypes was named by the formula or the law of Hardy-Weinberg, or the law of a stabilizing equilibrium, since it expresses a certain pattern that characterizes the population in the presence of free crossing in it. Such a population is in equilibrium at the ratio of genotypes, which is confirmed by the above formula:

Р ²aaa + 22pqaa + q²aa \u003d 1.

According to the Hardy-Weinberg law, the lack of factors defining and changing the frequency of genes, the population at any ratio of alleles from generation to generation retains these frequencies permanent. Despite some limitations, according to the Hardy-Weinberg formula, it is possible to calculate the structure of the population and determine the frequencies of heterozygotes, for example, by lethal or sublotheal genes, knowing the homogenic frequencies on recessive features and frequencies of individuals with dominant signs, to analyze shifts in gene frequencies on specific features as a result Selection, mutations and other factors.

In all populations of laboratory animals and in nature, with free crossing, there is a splitting on a given amount of genes that determine a variety of morphological and physiological signs. In some cases, the alleles of individual genes are relatively easy to select and the alleles of individual genes are presented, and then the grandiose picture of the genetic complexity of the population will have.

This is the case with the analysis of the genetic structure of populations in animals, but we need to know the factors capable of changing this structure. There are a lot of them, but the most important place belongs to the selection.

Under the selection in the classic sense, the word usually understand the elimination of a certain group of individuals from reproduction, i.e. the formation of the next generation. In the absence of selection, each individual population has the same chances to give offspring. Although they are random, but characterized by a normal distribution curve.

If a group of individuals is eliminated from reproduction, then the structure of the future generation will affect the only remaining part of the population, which will inevitably affect the incidence of genes in the next generation. However, K. Pearson showed that as soon as the state of the pamixia occurs (free crossing), the ratio of genotypes returns to the type that corresponds to the Hardy-Weinberg formula, but in the other ratio. Thus, in the absence of brave of heterozygous carriers of recessive anomalies, the frequency of the appearance of abnormal animals in the population remains unchanged.

Value Population Genetics: Basic concepts of population genetics in the Color Dictionary

Population genetics: Basic concepts of population genetics

To the article population genetics

Frequencies of genotypes and alleles. The most important concept of population genetics is the frequency of the genotype - the proportion of individuals in the population with this genotype. Consider an autosomal gene with k alleles, A1, A2, ..., AK. Let the population consist of N individuals, some of which has alleles AI AJ. Denote the number of these individuals Nij. Then the frequency of this genotype (Pij) is defined as Pij \u003d Nij / n. Let, for example, a gene has three alleles: A1, A2 and A3 - and let the population consist of 100,000 individuals, among which there are 500, 1000 and 2000 homozygot A1A1, A1A2, A1A3 and A2A3 - 1000, 2500 and A2A3 - 1000, 2500 3000, respectively. Then the frequency of the homozygot A1A1 is p11 \u003d 500/10000 \u003d 0.05, or 5%. Thus, we obtain the following observed homo- and heterozygotes:

P11 \u003d 0.05, p22 \u003d 0.10, p33 \u003d 0.20,

P12 \u003d 0,10, p13 \u003d 0.25, p23 \u003d 0.30.

Another important concept of population genetics is the frequency of the allele - its share among having alleles. Denote the frequency of allele AI as PI. Since the heterozygous individual alleles are different, the allele frequency is equal to the sum of the frequency of homozygous and half the frequencies of heterozygous in this allele of individuals. This is expressed as follows: pi \u003d pii + 0.5 ?? jpij. In the given example, the frequency of the first allele is p1 \u003d p11 + 0.5? (P12 + p13) \u003d 0.225. Accordingly, p2 \u003d 0,300, p3 \u003d 0.475.

The ratio of Hardy - Weinberg. In the study of the genetic dynamics of populations, a population with a random crossing, having an infinite number and isolated from the influx of migrants, is taken as the theoretical, "zero" point of reference. It is also believed that the pace of mutating genes is negligible small and the selection is absent. It mathematically proves that in such a population of the frequency of the autosomal gene alleles is the same for females and males and do not change from generation to generation, and the frequencies of homo- and heterozygotes are expressed through the frequencies of alleles as follows:

Pii \u003d pi2, pij \u003d 2pi pj.

This is called relations, or law, Hardy - Weinberg - named English Mathematics Ghardi and German Medica and Statistics V. V. V. V. V. Wereinberg, at the same time independently opened them: the first - theoretically, the second - from the data to inherit signs in humans.

Real populations can differ significantly from the ideal described Hardy - Weinberg equations. Therefore, the observed frequencies of genotypes deviate from the theoretical values \u200b\u200bcalculated by the ratios of Hardy - Weinberg. Thus, in the example above, the theoretical frequencies of genotypes differ from the observed and constitute

P11 \u003d 0,0506, p22 \u003d 0.0900, p33 \u003d 0,2256,

P12 \u003d 0,1350, p13 \u003d 0,2138, p23 \u003d 0.2850.

Such deviations can be partially explained by the so-called. sampling error; After all, in fact, in the experiment, not the whole population is studied, but only individual individuals, i.e. sample. But main reason Deviations of the frequencies of genotypes are undoubtedly those processes that flow in populations and affect their genetic structure. We describe them consistently.

Population-genetic processes

Draif genes. Under the gene drift, random changes of gene frequencies, caused by the final population number, are understood. To understand how a gene drift occurs, we first consider the population of the minimum possible number N \u003d 2: one male and one female. Suppose in the initial generation, the female has a genotype A1A2, and the male - A3A4. Thus, in the initial (zero) generation of the frequency of alleles A1, A2, A3 and A4 are 0.25 each. The individual of the next generation can be equally only one of the following genotypes: A1A3, A1A4, A2A3 and A2A4. Suppose the female will have a genotype A1A3, and the male - A2a3. Then in the first generation, the A4 allele is lost, the alleles A1 and A2 retain the same frequencies as in the initial generation - 0.25 and 0.25, and the allele A3 increases the frequency to 0.5. In the second generation, the female and the male can also have any combination of parent alleles, for example A1A2 and A1A2. In this case, it turns out that allel A3, despite the greater frequency, disappeared from the population, and the alleles A1 and A2 increased their frequency (p1 \u003d 0.5, p2 \u003d 0.5). The fluctuations of their frequencies will eventually lead to the fact that either Allel A1 or Allel A2 will remain in the population; In other words, the male and the female will be homozygous by the same allele: A1 or A2. The situation could have to work out and so that the Allel A3 or A4 would remain in the population, but this did not happen in the case.

The process of the gene drift process described by us takes place in any population of the final number, with the only difference that events are developing with a much lesser rate than with numbers in two individuals. The gene drift has two important consequences. First, each population loses genetic variability at speed, inversely proportional to its number. Over time, some alleles become rare, and then disappear at all. In the end, in the population there is a single allele from the existed, which is the case of the case. Secondly, if the population is divided into two or greater number of new independent populations, the gene drift leads to increasing differences between them: in some populations there are alone alleles, and in others - others. Processes that counteract the loss of variability and genetic discrepancies of populations are mutations and migration.

Mutations. In the formation of Games, random events are occurring - mutations when the parent allel, say a1, turns into another allel (A2, A3 or any other), or not previously extended in the population. For example, if in the nucleotide sequence "... TCT TGG ...", coding a plot of the polypeptide chain "... serine-tryptophan ...", the third nucleotide, t, as a result, the mutation was transferred to the child as C, then in the appropriate The segment of the amino acid chain of a protein, synthesized in the body of a child, instead of a serine would be located alanine, because it encodes the TCC triplet (see heredity). Regularly emerging mutations and formed in long row Generations of all species living on Earth then a giant genetic diversity that we are currently observed.

The probability with which mutation occurs is called frequency, or tempo, mutation. The pace of mutation of different genes varies from 10-4 to 10-7 per generation. At first glance, these values \u200b\u200bseem insignificant. However, it should be noted that, firstly, the genome contains many genes, and, secondly, the population may have a significant number. Therefore, part of the Games always carries mutant alleles, and almost every generation appears one or more individuals with mutations. Their destiny depends on how much these mutations affect the fitness and fertility. The mutation process leads to an increase in the genetic variability of populations, counteracting the effect of gene drift.

Migration. The population of one species is not isolated from each other: there is always an exchange of individuals - migration. Migrating individuals, leaving the offspring, transmit the next generations of alleles, which in this population could not even be or they were rare; This is how the flow of genes from one population to another is formed. Migration, as well as mutations, lead to an increase in genetic diversity. In addition, the flow of genes binding the population leads to their genetic similarity.

Crossing systems. In population genetics, crossing is called random if genotypes of individuals do not affect the formation of marriage steam. For example, in groups of blood, crossing can be considered random. However, painting, dimensions, behavior can greatly affect the choice of sexual partner. If preference is the individuals of a similar phenotype (i.e. with similar individual characteristics), such a positive assortive crossing leads to an increase in the population of individuals with parental genotype. If, with the selection of a marriage pair, preferences have individuals of the opposite phenotype (negative assortive crossing), then new combinations of alleles will be presented in the genotype of offspring; Accordingly, the population will appear individuals or an intermediate phenotype, or a phenotype, sharply different from the phenotype of parents.

In many regions of the world, the frequency of nearby marriages is high (for example, between cousins \u200b\u200band secondary relatives). The formation of marriage pairs based on kinship is called inbreeding. Inbreeding increases the proportion of homozygous individuals in the population, since in this case there is a high probability that parents have similar alleles. With an increase in the number of homozygotes, the number of patients with recessive hereditary diseases increases. But inbreeding also contributes to a greater concentration of certain genes, which can provide best adaptation This population.

Selection. Differences in fertility, survival, sexual activity, etc. They lead to the fact that some individuals leave more inadequate descendants than others - with a different set of genes. The different contribution of individuals with different genotypes to reproduce the population is called selection.

Changes in nucleotides can affect, and may not affect the product of the gene - a polypeptide chain and produced by it protein. For example, serine amino acid is encoded with six different triplets - TCC, TCG, TCT, TCC, AGT and AGC. Therefore, the mutation can turn one of these triplets to another, but not to change the amino acid itself. In contrast, the amino acid tryptophan is encoded only by one triplet - TGG, and therefore any mutation will replace tryptophan on another amino acid, for example, on arginine (TsGG) or serine (TCG), or even lead to a cliff of the synthesized polypeptide chain, if the so-called will appear as a result of the mutation . Stop codon (TGA or TAG). Differences between variants (or forms) protein can be invisible to the body, but can and significantly affect its livelihood. For example, it is known that when in the 6th position of the beta chain of the hemoglobin of a person, instead of glutamic acid costs another amino acid, namely Valin, it leads to severe pathology - sickle-cell anemia. Changes in other parts of the hemoglobin molecule lead to other forms of pathology called hemoglobinopathy.

Even greater differences in fitness are observed by genes determining the size, physiological signs and behavior of individuals; There may be many such genes. The selection, as a rule, affects them all and can lead to the formation of associations of alleles of different genes.

Genetic population parameters. When describing populations or comparing them, a number of genetic characteristics are used.

Polymorphism. The population is called polymorphic on this locus if two or more alleles occurs in it. If the locus is represented by the only allele, they talk about monomorphism. Exploring many loci, it is possible to determine among them a fraction of polymorphic, i.e. Assess the degree of polymorphism, which is an indicator of the genetic diversity of the population.

Heterozygency. Important genetic characteristic The population is heterozygency - the frequency of heterozygous individuals in the population. It also reflects genetic diversity.

Inbreeding coefficient. With this coefficient, the prevalence of nearby crossings in the population is estimated.

Association of genes. The frequencies of alleles of different genes may depend on each other, which is characterized by the coefficients of the association.

Genetic distances. Different populations differ from each other in the frequency of alleles. For quantitative assessment of these differences, indicators called genetic distances are proposed.

Various population-genetic processes affect these parameters in different ways: inbreeding leads to a decrease in the share of heterozygous individuals; Mutations and migrations increase, and the drift reduces the genetic diversity of populations; The selection changes the frequencies of genes and genotypes; The gene drift increases, and migrations reduce genetic distances, etc. Knowing these patterns, you can quantify the genetic structure of populations and predict its possible changes. This promotes a solid theoretical base of population genetics - population-genetic processes mathematically formalized and described by the dynamics equations. Statistical models and criteria were developed for testing various hypotheses about genetic processes in populations.

By attaching these approaches and methods to the study of populations of man, animal, plants and microorganisms, many problems of evolution, ecology, medicine, selection, etc. can be solved. Consider several examples that demonstrate the connection of population genetics with other sciences.

Colter. Color dictionary. 2012

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The structure of the gene pool in the pamctic stationary population is described by the basic law of population genetics - hardy Weinberg Law which states that in an ideal population there is a constant ratio of relative frequencies of alleles and genotypes, which is described by the equation:

(P a + Q a) 2 \u003d P2 AA + 2 ∙ P ∙ Q AA + Q2 AA \u003d 1

If the relative frequencies of alleles p and q are known and the total number of novels is known, then the expected, or the estimated absolute frequency (that is, the number of individuals) of each genotype. For this, each member of the equation must be multiplied by Novel:

p2 aa · novel + 2 · p · q Aa · NOCH + Q2 AA · NOCH \u003d NORCH

In this equation:

p2 AA · NOCH - expected absolute frequency (number) of dominant homozygot AA

2 · p · Q AA · NOCH - expected absolute frequency (number) heterozygot AA

q2 AA · NOCH - expected absolute frequency (number) recessive homozygot AA

Effect of Hardy Weinberg Law with incomplete dominance

Consider the action of the Hardy-Weinberg law with incomplete dominance on the example of the inheritance of the wool in the fox. It is known that the main influence on the color of the wool in the fox is provided by the gene A, which exists in the form of two main alleles: a and a. Each possible genotype corresponds to a certain phenotype:

AA - Redhead, Aa - Silloduks, aa - black and brown (or silver)

On the procurement points of the Foon for many years (in Russia since the XVIII century), the skins are carried out. I will operate the book of accounting of the Lisk Skuffs on one of the procurement points of the North-East of Russia and choose an arbitrarily 100 consecutive records. Calculate the number of skins with different color. Suppose that the following results are obtained: redheads (AA) - 81 skin, Susyvoduks (AA) - 18 skins, black and brown (AA) - 1 skin.

Calculate the number (absolute frequency) of dominant alleles A, given that every fox is a diploid organism. The red foxes carry 2 allele A, their 81 individuals, only 2a × 81 \u003d 162a. Syvoruski carry 1 allele A, their 18 individuals, only 1a × 18 \u003d 18a. The total amount of dominant alleles Na \u003d 162 + 18 \u003d 180. Similarly, we calculate the number of recessive alleles A: in black and brown foxes 2a × 1 \u003d 2a, at Susyoduks 1a × 18 \u003d 18a, total amount Recessive alleles NA \u003d 2 + 18 \u003d 20.

The total number of all alleles of the gene A \u003d Na + Na \u003d 180 + 20 \u003d 200. We analyzed 100 individuals, each by 2 allele, the total amount of alleles is 2 × 100 \u003d 200. The number of alleles counted for each gene / phenotype, and the number Alleles calculated on the total number of individuals, in any case, is 200, it means that the calculations are carried out correctly.

We will find the relative frequency (or share) of the allele A with respect to the total number of alleles:

ra \u003d Na: (Na + Na) \u003d 180: 200 \u003d 0.9

Similarly, we find the relative frequency (or share) of the allele A:

qa \u003d Na: (Na + Na) \u003d 20: 200 \u003d 0.1

The sum of the relative frequencies of alleles in the population is described by the ratio:

ra + Qa \u003d 0,9 + 0.1 \u003d 1

The given equation is a quantitative description of the allelolineland of this population, reflects its structure. Since the accounting book is represented randomly, and the sample of 100 individuals is quite large enough, the results obtained can be generalized (extrapolate) to the entire population.

Consider the change in the structure of the allelofond (that is, the frequencies of all alleles) and the gene pool (that is, the frequencies of all genotypes) of this population when alternating generations. All males and females give allel a and a in the ratio of 0.9a: 0,1A.

This is the difference between the genetics of populations from classical genetics. When considering the laws of Mendel, the ratio of 1a: 1a was initially defined, since parents were always homozygous: AA and AA.

To find the relative frequencies of genotypes, make a lattice of the Pennet. At the same time, we take into account that the probability of a meeting of alleles in the zygote is equal to the product of the probabilities of finding each allele.

Hamets females	Gameta males
		silloduushki
	silloduushki	black and brown

We will find the final relative and absolute frequencies of genotypes and phenotypes:

Comparing the resulting result with the initial state of the population, we see that the structure of the alleloline and gene pool has not changed. Thus, in the considered population of Lis, the law Hardy-Weinberg is performed with perfect accuracy.

Action of the Law X Ardi-Weinberg with full dominance

Consider the action of the Hardy-Weinberg law with full dominance on the example of the inheritance of painting wool in cats.

It is known that the black color of the wool in cats is determined by the AA genotype. At the same time, the black color can be either solid, or partial. AA and AA genotypes determine all the rest of the variety of types of color, but the black color is completely absent.

Suppose that in one of the city's urban populations on about. Sakhalin of 100-viewed animals complete or partial black painting had 36 animals.

The direct calculation of the structure of the alleloline population in this case is impossible due to the complete domination: the homozygotes of AA and heterosigons AA phenotypically indistinguishable. According to the Hardy-Weinberg equation, the frequency of black cats is Q2 AA. Then you can calculate the frequencies of alleles:

q2aa \u003d 36/100 \u003d 0.36; Qa \u003d 0.36 -1/2 \u003d 0.6; PA \u003d 1 - 0.6 \u003d 0.4

Thus, the structure of the allelo component of this population is described by the relation: P A + Q A \u003d 0.4 + 0.6 \u003d 1. The frequency of the recessive allele was higher than the frequency of the dominant.

Calculate the frequencies of genotypes:

p2 aa \u003d 0.42 \u003d 0.16; 2 pq aa \u003d 2 '0,4' 0,6 \u003d 0.48; Q2aa \u003d 0.62 \u003d 0.36

However, to check the correctness of the calculations in this case is not possible, since the actual frequencies of dominant homozygotes and heterozygot are unknown.

3. Implementation of the Hardy-Weinberg law in natural populations. The practical importance of the Hardy Weinberg law

In some cases (for example, in the case of complete dominance), when describing the structure of the gene pool of natural populations, it is necessary to assume that they have the features of perfect populations.

Comparative characteristics of ideal and natural populations

Perfect population	Natural populations
1. The population is infinitely large, and random elimination (death) of part of individuals does not affect the structure of the population	1. The population consists of a finite number of individuals.
2. There is no sex differentiation, female and men's gates are equivalent (for example, with a homotage isolation in algae)	2. There are various types of sex differentiation, various methods Play I. various systems Crossing
3. The presence of pamilia - free crossing; the existence of a govetooth reservoir; Equalization of the meeting of Games and the formation of the zygota regardless of the genotype and age of parents	3. There is a selectivity in the formation of marriage steam, when meeting Games and the education of the zygote
4. There are no mutations in the population	4. Mutations always occur
5. There is no natural selection in the population	5. There is always differential reproduction of genotypes, including differential survival and differential success in reproduction
6. The population is isolated from other populations of this species.	6. There are migrations - the flow of genes

In most studied populations of deviations from these conditions, usually do not affect the implementation of the Hardy-Weinberg law. It means that:

- the number of natural populations is quite large;

- female and men's gates are equivalent; males and females equally transfer their alleles to descendants);

- most genes do not affect the formation of marriage pairs;

- mutations occur quite rarely;

- Natural selection does not have a noticeable effect on the frequency of most alleles;

- populations are sufficiently isolated from each other.

If the Hardy-Weinberg law is not performed, then the deviations from the calculated values \u200b\u200binclude the effect of limited numbers, the difference between females and males when transmitting alleles to descendants, the absence of free crossing, the presence of mutations, the effect of natural selection, the presence of migration ties between populations.

In real studies, there are always deviations of empirical, or actual absolute frequencies (NFAK or NF) on the calculated, or theoretical (NFR, NTOR or NT). Therefore, the question arises: are these deviations or random, are these deviations, in other words, are reliable or unreliable? To answer this question, you need to know the actual frequencies of dominant homozygotes and heterozygotes. Therefore, in population-genetic studies, the detection of heterozygot plays a very important role.

The practical importance of the Hardy Weinberg law

1. In health care - It allows you to estimate the population risk of genetically determined diseases, since each population has its own alleloofond and, accordingly, different frequencies of adverse alleles. Knowing the birth rate of children with hereditary diseases, you can calculate the structure of the alleloline. At the same time, knowing the frequency of adverse alleles, you can predict the risk of birth of a patient child.

Example 1. It is known that albinism is an autosomal-recessive disease. It was established that in most European populations, the frequency of the birth of albino children is 1 to 20 thousand newborns. Hence,

q2aa \u003d 1/20000 \u003d 0.00005; Qa \u003d 0.00005-1 / 2 \u003d 0.007; PA \u003d 1 - 0.007 \u003d 0.993 ≈ 1

Since for rare diseases of Ra ≈ 1, the frequency of heterozygous carriers can be calculated by formula 2 · q. In this population, the frequency of heterozygous carriers of albinism allele is 2 Q AA \u003d 2 '0.007 \u003d 0.014, or about each seventy member of the population.

Example 2. Let in one of the populations in 1% of the population revealed a recessive allele, which is not found in a homozygous state (it can be assumed that in a homozygous state this allele is flying). Then 2 Q AA \u003d 0.01, therefore, Qa \u003d 0.01: 2 \u003d 0.005. Knowing the frequency of a recessive allele, you can set the frequency of the destruction of the germ-homozygot: Q2aa \u003d 0.0052 \u003d 0.000025 (25 per million, or 1 to 40 thousand).

2. In breeding - Allows you to identify the genetic potential of the source material (natural populations, as well as varieties and rocks of folk selection), since different varieties and rocks are characterized by their own allelo-founders, which can be calculated using the Hardy Weinberg law. If a high frequency of the required allele is revealed in the source material, then you can expect a quick preparation of the desired result during the selection. If the frequency of the required allele is low, then you need to or look for another source material, or enter the desired allele from other populations (varieties and rocks).

3. In ecology - Allows you to identify the influence of a wide variety of factors on the population. The fact is that, remaining phenotypically homogeneous, the population can significantly change its genetic structure under the influence of ionizing radiation, electromagnetic fields and other adverse factors. According to the deviations of the actual frequencies of genotypes on the calculated values, it is possible to establish the effect of environmental factors. (In this case, it is necessary to strictly observe the principle of the only difference. Let the influence of the content heavy metals In the soil on the genetic structure of populations of a certain type of plant. Then two populations inhabiting in extremely similar conditions should be compared. The only difference in habitat should be in different content of a certain metal in the soil).

The content of the article

Population genetics,the section of genetics, studying the genuofund of populations and its change in space and time. Tell in more detail in this definition. The individuals do not live by one, but form more or less stable groups, mastering the habitat. Such groupings, if they are self-reproduced in generations, and not supported only at the expense of the suppressed individuals, are called populations. For example, a flock of salmon, sprouting in the same river, forms a population, because the descendants of each fish from year to year are usually returned to the same river, the same spawning. In agricultural animals, the population is considered to be a breed: all individuals in it in one origin, i.e. They have common ancestors, are contained under similar conditions and are supported by a single breeding and tribal work. The aboriginal peoples population are members of the kinship-related core.

In the presence of migrations, the boundaries of populations are blurred and therefore indefunted. For example, the entire population of Europe is the descendants of therigonians who settled our continent tens of thousands of years ago. Isolation of ancient tribes, reinforced with the development of each of them its own language and culture, led to the differences between them. But their withdrawal was always relative. Permanent wars and seizures of territory, and recently - gigantic migration led and lead to a certain genetic rapprochement of peoples.

The above examples show that under the word "population" it is necessary to understand the grouping of individuals associated with territorial, historical and reproductive generality.

The individuals of each population differ from each other, and each of them is unique in something. Many of these differences are hereditary, or genetic - they are determined by genes and are transferred from parents to children.

The combination of genes of all individuals of this population is called its gene pool. In order to solve problems of ecology, demographics, evolution and breeding, it is important to know the features of the gene pool, namely: how great genetic diversity in each population, what are the genetic differences between the geographically separated populations of one species and between various specieshow the gene pool varies under the action ambienthow it is transformed during evolution, as the hereditary diseases are distributed, how effectively the gene pool is used cultural plants and domestic animals. Studying these issues and deals population genetics.

The basic concepts of population genetics

Frequencies of genotypes and alleles.

The most important concept of population genetics is the frequency of the genotype - the proportion of individuals in the population with this genotype. Consider an autosomal gene having k alleles, a 1, a 2, ..., a k. Let the population consist of n individuals, some of which has alleles a i a j. Denote the number of these individuals n ij. Then the frequency of this genotype (P ij) is defined as p ij \u003d n ij / n. Suppose, for example, the gene has three alleles: a 1, a 2 and a 3 - and let the population consists of 10,000 individuals, among which there are 500, 1000 and 2000 homozygot A 1 A 1, A 2 A 2 and A 3 A 3, And heterozygot A 1 A 2, A 1 A 3 and A 2 A 3 - 1000, 2500 and 3000, respectively. Then the frequency of homozygot A 1 A 1 is p 11 \u003d 500/10000 \u003d 0.05, or 5%. Thus, we obtain the following observed homo- and heterozygotes:

P 11 \u003d 0.05, p 22 \u003d 0.10, p 33 \u003d 0.20,

P 12 \u003d 0.10, p 13 \u003d 0.25, p 23 \u003d 0.30.

Another important concept of population genetics is the frequency of the allele - its share among having alleles. Denote the frequency of the allele A I as P i. Since the heterozygous individual alleles are different, the allele frequency is equal to the sum of the frequency of homozygous and half the frequencies of heterozygous in this allele of individuals. This is expressed by the following formula: P i \u003d P II + 0.5CH j p ij. In the above example, the frequency of the first allele is p 1 \u003d p 11 + 0.5 h (p 12 + p 13) \u003d 0.225. Accordingly, p 2 \u003d 0,300, p 3 \u003d 0.475.

The ratio of Hardy - Weinberg.

In the study of the genetic dynamics of populations, a population with a random crossing, having an infinite number and isolated from the inflow of migrants, is taken as a theoretical, "zero" point of reference. It is also believed that the pace of mutating genes is negligible small and the selection is absent. It mathematically proves that in such a population of the frequency of the autosomal gene alleles is the same for females and males and do not change from generation to generation, and the frequencies of homo- and heterozygotes are expressed through the frequencies of alleles as follows:

P II \u003d P i 2, p ij \u003d 2p i p j.

This is called relations, or law, Hardy - Weinberg - named English Mathematics Ghardi and German Medica and Statistics V. V. V. V. V. Wereinberg, at the same time independently opened them: the first - theoretically, the second - from the data to inherit signs in humans.

Real populations can differ significantly from the ideal described Hardy - Weinberg equations. Therefore, the observed frequencies of genotypes deviate from the theoretical values \u200b\u200bcalculated by the ratios of Hardy - Weinberg. Thus, in the example above, the theoretical frequencies of genotypes differ from the observed and constitute

P 11 \u003d 0,0506, p 22 \u003d 0.0900, p 33 \u003d 0,2256,

P 12 \u003d 0.1350, p 13 \u003d 0.2138, p 23 \u003d 0.2850.

Such deviations can be partially explained by the so-called. sampling error; After all, in fact, in the experiment, not the whole population is studied, but only individual individuals, i.e. sample. But the main reason for the deviation of the genotype frequencies is undoubtedly those processes that flow in populations and affect their genetic structure. We describe them consistently.

Population-genetic processes

Draif genes.

Under the gene drift, random changes of gene frequencies, caused by the final population number, are understood. To understand how a gene drift occurs, we first consider the population of the minimum possible number N \u003d 2: one male and one female. Suppose in the initial generation, the female has genotype A 1 A 2, and the male - a 3 A 4. Thus, in the initial (zero) generation of the frequency of alleles A 1, A 2, A 3 and A 4 are 0.25 each. Next generation individuals can be equally only one of the following genotypes: A 1 A 3, A 1 A 4, A 2 A 3 and A 2 A 4. Suppose that the female will have genotype A 1 A 3, and the male - A 2 A 3. Then in the first generation, the allele A 4 is lost, the alleles A 1 and A 2 retain the same frequencies as in the original generation - 0.25 and 0.25, and Allel A 3 increases the frequency to 0.5. In the second generation, the female and the male can also have any combination of parental alleles, for example A 1 A 2 and A 1 A 2. In this case, it turns out that Allel A 3, despite the greater frequency, disappeared from the population, and the alleles A 1 and A 2 increased their frequency (p 1 \u003d 0.5, p 2 \u003d 0.5). The fluctuations of their frequencies will eventually lead to the fact that the population will remain either allel a 1 or allele A 2; In other words, the male and the female will be homozygous by the same allele: a 1 or a 2. The situation could be formed and so that allele A 3 or A 4 would remain in the population, but this did not happen in the case.

The process of the gene drift process described by us takes place in any population of the final number, with the only difference that events are developing with a much lesser rate than with numbers in two individuals. The gene drift has two important consequences. First, each population loses genetic variability at speed, inversely proportional to its number. Over time, some alleles become rare, and then disappear at all. In the end, in the population there is a single allele from the existed, which is the case of the case. Secondly, if the population is divided into two or greater number of new independent populations, the gene drift leads to increasing differences between them: in some populations there are alone alleles, and in others - others. Processes that counteract the loss of variability and genetic discrepancies of populations are mutations and migration.

Mutations.

In the formation of Games, random events occur - mutations when the parent allel, say a 1, turns into another allel (a 2, a 3 or any other), or not previously extended in the population. For example, if in the nucleotide sequence "... TCT TGG ...", the coding section of the polypeptide chain "... serine-tryptophan ...", the third nucleotide, t, as a result of mutation, the child was transferred as a child, then in the appropriate section of the amino acid chain of the protein, synthesized in the body Child, instead of a serine would be located alanine, because it encodes the TCC triplet ( cm. Heredity). Regularly emerging mutations and formed in a long row of generations of all species living on Earth, the gigantic genetic diversity, which we now observe.

The probability with which mutation occurs is called frequency, or tempo, mutation. The pace of mutation of different genes varies from 10 -4 to 10 -7 to generation. At first glance, these values \u200b\u200bseem insignificant. However, it should be noted that, firstly, the genome contains many genes, and, secondly, the population may have a significant number. Therefore, part of the Games always carries mutant alleles, and almost every generation appears one or more individuals with mutations. Their destiny depends on how much these mutations affect the fitness and fertility. The mutation process leads to an increase in the genetic variability of populations, counteracting the effect of gene drift.

Migration.

The population of one species is not isolated from each other: there is always an exchange of individuals - migration. Migrating individuals, leaving the offspring, transmit the next generations of alleles, which in this population could not even be or they were rare; This is how the flow of genes from one population to another is formed. Migration, as well as mutations, lead to an increase in genetic diversity. In addition, the flow of genes binding the population leads to their genetic similarity.

Crossing systems.

In population genetics, crossing is called random if genotypes of individuals do not affect the formation of marriage steam. For example, in groups of blood, crossing can be considered random. However, painting, dimensions, behavior can greatly affect the choice of sexual partner. If preference is the individuals of a similar phenotype (i.e. with similar individual characteristics), such a positive assortive crossing leads to an increase in the population of individuals with parental genotype. If, with the selection of a marriage pair, preferences have individuals of the opposite phenotype (negative assortive crossing), then new combinations of alleles will be presented in the genotype of offspring; Accordingly, the population will appear individuals or an intermediate phenotype, or a phenotype, sharply different from the phenotype of parents.

In many regions of the world, the frequency of nearby marriages is high (for example, between cousins \u200b\u200band secondary relatives). The formation of marriage pairs based on kinship is called inbreeding. Inbreeding increases the proportion of homozygous individuals in the population, since in this case there is a high probability that parents have similar alleles. With an increase in the number of homozygotes, the number of patients with recessive hereditary diseases increases. But inbreeding also contributes to a greater concentration of certain genes, which can provide better adaptation of this population.

Selection.

Differences in fertility, survival, sexual activity, etc. They lead to the fact that some individuals leave more inadequate descendants than others - with a different set of genes. The different contribution of individuals with different genotypes to reproduce the population is called selection.

Changes in nucleotides can affect, and may not affect the product of the gene - a polypeptide chain and produced by it protein. For example, serine amino acid is encoded with six different triplets - TCC, TCG, TCT, TCC, AGT and AGC. Therefore, the mutation can turn one of these triplets to another, but not to change the amino acid itself. In contrast, the amino acid tryptophan is encoded only by one triplet - TGG, and therefore any mutation will replace tryptophan on another amino acid, for example, on arginine (TsGG) or serine (TCG), or even lead to a cliff of the synthesized polypeptide chain, if the so-called will appear as a result of the mutation . Stop codon (TGA or TAG). Differences between variants (or forms) protein can be invisible to the body, but can and significantly affect its livelihood. For example, it is known that when in the 6th position of the beta chain of the hemoglobin of a person, instead of glutamic acid costs another amino acid, namely Valin, it leads to severe pathology - sickle-cell anemia. Changes in other parts of the hemoglobin molecule lead to other forms of pathology called hemoglobinopathy.

Even greater differences in fitness are observed by genes determining the size, physiological signs and behavior of individuals; There may be many such genes. The selection, as a rule, affects them all and can lead to the formation of associations of alleles of different genes.

Genetic population parameters.

When describing populations or comparing them, a number of genetic characteristics are used.

Polymorphism.

The population is called polymorphic on this locus if two or more alleles occurs in it. If the locus is represented by the only allele, they talk about monomorphism. Exploring many loci, it is possible to determine among them a fraction of polymorphic, i.e. estimate powerpolymorphism, which is an indicator of the genetic diversity of the population.

Heterozygency.

An important genetic characteristic of the population is heterozygency - the frequency of heterozygous individuals in the population. It also reflects genetic diversity.

Inbreeding coefficient.

With this coefficient, the prevalence of nearby crossings in the population is estimated.

Association of genes.

The frequencies of alleles of different genes may depend on each other, which is characterized by coefficients association.

Genetic distances.

Different populations differ from each other in the frequency of alleles. For quantitative assessment of these differences, indicators called genetic distances are proposed.

Various population-genetic processes affect these parameters in different ways: inbreeding leads to a decrease in the share of heterozygous individuals; Mutations and migrations increase, and the drift reduces the genetic diversity of populations; The selection changes the frequencies of genes and genotypes; The gene drift increases, and migrations reduce genetic distances, etc. Knowing these patterns, you can quantify the genetic structure of populations and predict its possible changes. This promotes a solid theoretical base of population genetics - population-genetic processes mathematically formalized and described by the dynamics equations. Statistical models and criteria were developed for testing various hypotheses about genetic processes in populations.

By attaching these approaches and methods to the study of populations of man, animal, plants and microorganisms, many problems of evolution, ecology, medicine, selection, etc. can be solved. Consider several examples that demonstrate the connection of population genetics with other sciences.

Population genetics and evolution

Often think that the main merit of Charles Darwin is that he opened the phenomenon biological evolution. However, this is not so. Before the publication of his book Origin of species (1859) Biologists constructed believe that the old species generate new ones. Disagreements were only in understanding how exactly it could happen. The most popular was the hypothesis of Jean Batista Lamarck, according to which during life every organism changes in the direction corresponding to the environment in which he lives, and these useful changes ("Transferred" signs) are transmitted to descendants. With all its attractiveness, this hypothesis has not been inspected by genetic experiments.

On the contrary, the evolutionary theory, developed by Darwin, argued that 1) the individuals of the same species differ from each other in many signs; 2) these differences can provide adaptation to different conditions environments; 3) These differences are hereditary. In terms of population genetics, these provisions can be formulated as follows: a greater contribution to the following generations are given those individuals that have the most suitable for this environment of genotypes. Change medium, and the selection of genes will begin, more relevant to new conditions. Thus, from Darwin's theory it follows that genophonds evolve.

Evolution can be defined as an irreversible change in the agelons of populations in time. It is performed by accumulating the mutation changes of DNA, the emergence of new genes, chromosomal transformations, etc. The important role is played by the fact that the genes have the ability to double (duplicated), and their copies are integrated into chromosome. As an example, turn back to hemoglobin. It is known that the genes of the alpha and beta chains occurred by the duplication of a certain ancestor gene, which, in turn, occurred from the ancestor of the gene encoding the Mioglobin protein - the carrier of oxygen in the muscles. Evolutionary this led to the occurrence of hemoglobin - molecules with a tetramer structure consisting of four polypeptide chains: two alpha and two beta. After the nature of "found" the tetramer structure of hemoglobin (vertebrates), the remaining types of structures for oxygen transport turned out to be practically non-competitive. Then, for tens of millions of years, they arose and selected best options Hemoglobin (its own - in each evolutionary branch of animals), but within the tetramer structure. Today's selection on this basis in humans became conservative: he "protects" the only past millions of generations of hemoglobin variant, and any replacement in any of the chains of this molecule leads to illness. However, many vertebrate species have two or more equal hemoglobin options - the selection "encouraged" them equally. And a person has proteins for which the evolution "left" several options.

Population genetics allows us to estimate the time when certain events in evolutionary history occurred. Return again for example with hemoglobin. Let, for example, it is desirable to evaluate the time when the ancestral genes of alpha and beta chains occurred and, therefore, such a respiratory system originated. We analyze the structure of these polypeptide chains in a person or any animal and comparing them, determine how much the corresponding nucleotide sequences differ from each other. Since both ancestor chains have been identical at the beginning of its evolutionary history, then, knowing the speed of replacement of one nucleotide to another and the number of differences in compared circuits, you can find out from the moment of their duplication. Thus, here proteins act as peculiar "molecular hours." Another example. Comparing hemoglobin or other proteins in humans and primates, you can evaluate how many millions of years ago our overall ancestor. Currently, "silent", non-coding DNA sections, less susceptible to external influences, are used as molecular hours.

The population genetics allows you to look into the depths of centuries and sheds the light on such events in the evolutionary history of mankind, which could not be found out on modern archaeological findings. So, quite recently, comparing the gene pools of people from different parts Light, most scientists agreed that the overall ancestor of all races of a modern person arose about 150 thousand years ago in Africa, from where he settled on all continents through the front Asia. Moreover, comparing DNA of people in different regions Earth, you can estimate the time when the human populations began to grow in numbers. Studies show that this happened a few tens of thousands of years ago. Thus, in the study of the history of mankind, population-genetic data is beginning to play an equally important role as the data of archeology, demographics and linguistics.

Population genetics and ecology

The types of animals, plants and microorganisms in each region are formed by a holistic system known as an ecosystem. Each species is represented in her, a unique population. Evaluate the environmental well-being of this territory or water area allow the data characterizing its ecosystem gene phones, i.e. Genofund of the categories of its populations. It is he who provides the existence of an ecosystem in these conditions. Therefore, as amended in the ecological situation of the region, you can trace, studying the gene pools of populations inhabiting there.

Mastering new territories, laying oil and gas pipelines, should take care of the preservation and restoration of natural populations. Population genetics has already proposed its measures, for example, the allocation of natural genetic reservations. They must be quite extensive to contain the main gene effect of plants and animals of this region. The theoretical apparatus Population genetics allows you to determine the minimum number that is necessary for maintaining the genetic composition of the population so that there is no so-called in it. Inbreeding depression so that it contains the main genotypes inherent in this population, and could reproduce these genotypes. At the same time, each region should have its own natural genetic reserves. It is impossible to restore ruined threshers of the North Western Siberia., posts of pine seeds from Altai, Europe or Far East: After decades, it may be that "strangers" genetically adapted to local conditions. That is why environmentally competent industrial development of the territory must necessarily include population studies of regional ecosystems, allowing them to identify their genetic originality.

This applies not only to plants, but also to animals. The genuofund of a particular population of fish is evolutionally adapted to those conditions in which he dwells for many generations. Therefore, the introduction of fish from one natural reservoir to the other time leads to unpredictable consequences. For example, attempts to breed Sakhalin Gorbow in Caspians were unsuccessful, her gene pool was not able to "master" new habitats. The same pink salmon, introduced into the White Sea, left him and went to Norway, forming the temporary herds of "Russian salmon" there.

It should not be thought that only cost-effective types of plants and animals should be the main objects of nature concern for nature, such as wood breeds, Furst animals or fishing fish. Herbate plants and mosses, small mammals and insects - their populations and their gene pools on a par with all others provide the normal life of the territory. The same refers to microorganisms - thousands of their species inhabit the soil. The study of soil microbes is the task of not only microbiologists, but also population genetics.

The change in the gene pool of populations with rough interventions in nature is not detected immediately. Decades can pass before the consequences will become obvious in the form of the disappearance of some populations, and behind them - others related to the first.

Population genetics and medicine

One of the urgent issues of humanity is how to treat hereditary diseases. However, until recently, the formulation of such a question seemed fantastic. It was only about the prevention of hereditary diseases in the form of medical and genetic counseling. An experienced genetic physician, studying the history of the patient's disease and exploring how often the hereditary disease was manifested among his loved ones and distant relatives, made a conclusion about whether the patient may have a child with such pathology; And if any may, what is the probability of this event (for example, 1/2, 1/10, or 1/100). Based on this information, the spouses themselves decided to have a child or not to have.

The rapid development of molecular biology significantly brought us to the cherished goal - the treatment of hereditary diseases. To do this, first of all, it is necessary to find among many human genes, which is responsible for the disease. Population genetics helps solve this complex task.

Known genetic labels - so-called. DNA markers that allow you to note in the long yarn of DNA, let's say, each thousand or ten-thousand "Bead". Exploring the patient, his relatives and healthy persons from the population, can be installed which of the markers is connected to the genome of the disease. With the help of special mathematical methods Population genetics detect that section of DNA in which the gene is located. After that, molecular biologists are included in the work, which in detail the DNA segment in detail and find a defective gene. In this way, the genes of most hereditary diseases are mapped. Now doctors got the opportunity in the first months of pregnancy directly judge the health of the future child, and parents - to solve the issue, maintain or not to preserve pregnancy, if you know in advance that the child will be born sick. Moreover, attempts are already being made to correct the mistakes allowed by nature, eliminate the breakdowns in the genes.

With the help of DNA markers, you can not only search for diseases. Using them, conduct a kind of certification of individuals. Such a DNA identification is a common type of forensic examination, which allows to determine the paternity, identify children confused in the hospital, to identify the participants of the crime, victims of a catastrophe and hostilities.

Population genetics and selection

According to Darwin's theory, the selection in nature is sent only to direct benefits - survive and multiply. For example, a fish in the painting of the Palevo-smoking wool, and the lion is sandy-yellow. Coloring, like camouflage clothing, serves as a person merging with the terrain. This allows predators to imperceptibly sample to the victim or wait. Therefore, although the color variations constantly appear in nature, wild cats with such a "label" do not survive. Only a person with his taste addiction creates all the conditions for the lives of domestic cats of a wide variety of colors.

Turning to a settled lifestyle, people left from hunting animals and gathering plants to their reproduction, sharply reducing their dependence on nature cataclysms. Millenniums reproducing individuals with the necessary signs and thereby selecting the corresponding genes from gene pools of populations, people gradually created all those grades of home plants and the breed of animals that they surround. It was the same selection that Nature spent millions of years, but now the person sent by reason was the role of nature.

With the beginning of development, population genetics, i.e. from the middle of the 20th century, the selection went on a scientific path, namely on the way to predict a response to selection and choice optimal options selection work. For example, in cattle breeding, the tribal value of each animal is calculated immediately in many signs of productivity, determined not only in this animal, but also at his relatives (mothers, sisters, descendants, etc.). All this comes down to a general index, taking into account both the genetic conditionality of signs of productivity and their economic significance. This is especially important when evaluating manufacturers who cannot determine their own productivity (for example, in bulls in dairy cattle breeding or in the roosters of egg rocks). With the introduction of artificial insemination, there was a need for a versatile population assessment of the tribal value of producers when used in different herds with different levels Feeding, maintenance and productivity. In plant selection, the population approach helps to quantify the genetic ability of lines and varieties to give promising hybrids and predict their fitness and productivity in different climate and soil regions.

Population genetics
The section of genetics, studying the genuofund of populations and its change in space and time. Tell in more detail in this definition. The individuals do not live by one, but form more or less stable groups, mastering the habitat. Such groupings, if they are self-reproduced in generations, and not supported only at the expense of the suppressed individuals, are called populations. For example, a flock of salmon, sprouting in the same river, forms a population, because the descendants of each fish from year to year are usually returned to the same river, the same spawning. In agricultural animals, the population is considered to be a breed: all individuals in it in one origin, i.e. They have common ancestors, are contained under similar conditions and are supported by a single breeding and tribal work. The aboriginal peoples population are members of the kinship-related core. In the presence of migrations, the boundaries of populations are blurred and therefore indefunted. For example, the entire population of Europe is the descendants of therigonians who settled our continent tens of thousands of years ago. Isolation between the ancient tribes, increased with the development of each of them its own language and culture, led to the differences between them. But the separation of them is relative. Permanent wars and seizures of territory, and recently - gigantic migration led and lead to a certain genetic rapprochement of peoples. The above examples show that under the word "population" it is necessary to understand the grouping of individuals associated with territorial, historical and reproductive generality. The individuals of each population differ from each other, and each of them is unique in something. Many of these differences are hereditary, or genetic - they are determined by genes and are transferred from parents to children. The combination of genes in individuals of this population is called its gene pool. In order to solve the problems of ecology, demographics, evolution and selection, it is important to know the features of the gene pool, namely: how great genetic diversity in each population, what are the genetic differences between the geographically separated populations of one species and between different types, as the gene pool varies under the action of the environment How it is transformed during evolution, as the hereditary diseases are distributed, how efficiently the gene effect of cultivated plants and domestic animals is used. The study of these issues and is engaged in population genetics.
The basic concepts of population genetics
Frequencies of genotypes and alleles. The most important concept of population genetics is the frequency of the genotype - the proportion of individuals in the population with this genotype. Consider an autosomal gene with k alleles, A1, A2, ..., AK. Let the population consist of N individuals, some of which has alleles AI AJ. Denote the number of these individuals Nij. Then the frequency of this genotype (Pij) is defined as Pij \u003d Nij / n. Let, for example, a gene has three alleles: A1, A2 and A3 - and let the population consist of 100,000 individuals, among which there are 500, 1000 and 2000 homozygot A1A1, A1A2, A1A3 and A2A3 - 1000, 2500 and A2A3 - 1000, 2500 3000, respectively. Then the frequency of the homozygot A1A1 is p11 \u003d 500/10000 \u003d 0.05, or 5%. Thus, we obtain the following observed homo- and heterozygotes:

P11 \u003d 0.05, p22 \u003d 0.10, p33 \u003d 0.20, p12 \u003d 0.10, p13 \u003d 0.25, p23 \u003d 0.30.

Change the frequencies of alleles during drift. The results of modeling the process of gene drift in two populations of n \u003d 25 and two populations of n \u003d 250, with an allele frequency of 0.5 in the initial generation. Under the action of the drift, the frequency of this allele is changing from generation to generation, and the "jumps" frequencies are more pronounced in populations of less numerous. For 50 generations, the drift led to the fixation of the allele in one population of n \u003d 25, and to its full elimination - to another. In populations large number This allel is still at intermediate frequencies, but the populations are already noticeably different from each other since the 60th generation.

LITERATURE
Timofeev-Resovsky N.V., Yablokov A.V., Glotov N.V. Essay of the teachings about the population. M., 1973 Ayala F., Kaigr J. Modern genetics, TT. 1-3, M., 1988 Fogel F., Motulski A. Genetics of a person, TT. 1-3. M., 1990.

The encyclopedia of the colley. - Open Society. 2000 .