Genetic balance in populations and its disturbances. Genetic balance in populations and its disturbances - Knowledge Hypermarket

Question 1. What changes in the gene pool allow us to conclude about the evolutionary changes taking place in the population?

The evolutionary changes taking place in a population can be judged by changes in the external structure of organisms, the characteristics of their behavior and lifestyle, and, ultimately, by the better adaptation of the population to given environmental conditions. The ongoing changes are the result of an increase in the frequencies of some genes in the gene pool and a decrease in the frequencies of others.

Question 2. What is genetic balance? Under what conditions is it possible?

Genetic equilibrium - the state of the gene pool of a population, in which there is a constancy of allele frequencies of various genes. It is possible only under conditions of weak pressure of natural selection, when the population lives in isolation.

Question 3. What factors are the cause of genetic imbalance in conditions where natural selection does not work?

In addition to natural selection, the following factors lead to the violation of the genetic balance in the population:

1) non-random selection of partners during mating, characteristic of some animals;

2) the loss of some rare species, for example, due to the death of their carriers (the smaller the population, the greater the impact of random factors on its gene pool);

3) division of the population into two unequal parts by some unexpected natural or artificial barriers;

4) the transfer by the population of any catastrophe that led to the death of most of it.

(!LANG:Popular Essays

GENETIC BALANCE
IN POPULATIONS AND ITS DISTURBANCES

Tasks: to acquaint students with the concept of genetic equilibrium in populations, to identify the causes of its violation.

Content elements: population genetics, genetic equilibrium.

Lesson type: combined.

Equipment: table "Genetic balance in populations".

During the classes

I. Organizing time.

II. Checking students' knowledge.

Biological dictation.

1. Who first tried to develop the theory of evolution?

2. Selection, in which features that are useful to a person are selected.

3. The properties of the organism to acquire new features.

4. What evolves according to the theory of Ch. Darwin.

5. Type of variability, which is the basis of the evolutionary process.

6. The sum of all genotypes present in the population.

7. English scientist who laid the foundations of the modern theory of evolution.

8. Driving force of evolution.

9. Ch. Darwin put three factors as the basis for explaining the causes of evolution: natural selection, variability of organisms and ...

10. Factors responsible for the variability of the genotype.

1) J.-B. Lamarck;

2) artificial;

3) variability;

4) species and populations;

5) hereditary;

6) gene pool;

7) C. Darwin;

8) natural selection;

9) struggle for existence;

10) mutations, recombinations of genes.

III. Learning new material.

The advent of population genetics helped to reveal the patterns that govern changes in the gene pool of a population. It was found that in many populations there is a constancy of allele frequencies of various genes, that is, genetic equilibrium.

population is elementary unit of evolution. A population is a group of individuals of the same species that freely interbreed and inhabit a certain area, relatively isolated from other groups of individuals of the same species.

In some cases, the genetic balance in a population may be disturbed, which leads to a change in the population as a whole.

Causes of genetic imbalance.

1. Non-standard choice of a partner when crossing.

2. Death of individuals (loss of genes responsible for a certain
sign).

3. Artificial and natural isolation of part of the population (creation of reservoirs, fire, etc.).

4. Disasters: when most individuals die, units remain that determine the gene pool of a new population.

5. As a result of natural selection, some signs are swept aside and other signs are fixed.

6. When developing new territories, new signs appear that determine the new gene pool.

Reasons: 1-4 - non-directional nature of the changes;

Remember!

Evolutionary changes in populations are always accompanied by directed changes in the gene pool that occur under the influence of natural selection. This ensures the difference between populations of the same species, which subsequently leads to their transformation into new species.

IV. Consolidation of the studied material.

Conversation on:

1. What is genetic balance? Under what conditions is it possible?

2. What factors are the cause of genetic imbalance?

3. What is the role of natural selection in changing the gene pool of a population?

Homework:§ 7.3.

GENE POOL - the sum of all genotypes present in a population. Patterns of changes in the gene pool of a population: the constancy of allele frequencies of various genes

Hardy-Weinberg law The frequency of genes (genotypes) in a population is a constant value and does not change from generation to generation. The balance of gene frequencies: p pq + q 2 \u003d 1, where p 2 is the frequency of dominant homozygotes (AA); 2 pq - frequency of heterozygotes (Aa); q 2 - the frequency of recessive homozygotes (a).

Biological task to fix the law a) b) In the population of the lake frog, offspring of frogs with dark spots (dominant trait) and 320 frogs with light spots appeared. Determine a) the frequency of occurrence of dominant and recessive spotting genes b) the number of heterozygotes among frogs with dark spots = 2000 individuals in total in the population. - the frequency of occurrence of homozygotes for the recessive. p \u003d 1 - q \u003d 1 - 0.4 \u003d 0.6 - the frequency of occurrence of homozygotes for the dominant. 2 pq \u003d 2 x 0.6 x 0.4 \u003d 0.48 \u003d 48% of 1680 will be heterozygotes. frequency of heterozygotes p pq + q 2 \u003d 1 \u003d 2000

Causes of violation of the genetic balance 3. When a population breaks up into two unequal parts by insurmountable barriers (If the number of individuals of one of the populations is small, its composition may differ from the previous one. Rare alleles may become common and vice versa).

Solving problems on the Hardy-Weinberg law 1. Albinism in rye is inherited as an autosomal recessive trait. On examination of a plot of plants, 210 albinisms were found. Determine the frequency of albinism genes in rye. Given: a - albinism A - norm Alb 210 norm 8400 Frequency q(a) - ? = (p + q) 2 = p pq + q 2 = 1 or = 5% (0.05 x 100%) q2q2 = q == = = 0.05 or 5%

Solving problems on the Hardy-Weinberg law 2. Foxes were shot on one of the islands. Of these, 9991 were red and 9 were white. Red color dominates over white. Determine the percentage of red homozygous, red heterozygous foxes and white foxes. Given: A - red and - white q 2, 2pq, p 2 -? (p + q) 2 = p pq + q 2 = 1 p = 1 - 0.03 = 0.97 q2q2 = q = = = 0.03 = 0.0009 = 0.09% p 2 = 0.97 2 \u003d 0.9409 \u003d 94% 2 pq \u003d 2 x 0.97 x 0.03 \u003d 0.0582 \u003d 5.8% Answer: a - 0.03%; Aa - 5.8%; AA - 94%

Solving problems on the Hardy-Weinberg law 3. Albinism is inherited as a recessive autosomal trait. The disease occurs with a frequency of 1: Calculate the percentage of heterozygotes in the population. Given: a – albinism A – norm Alb 1 norm Frequency 2 рq - ? = (p + q) 2 = p pq + q 2 = 1 p = 1 - 0.0071 = 0.9924 q2q2 = q = = 0.0071 Answer: number of heterozygotes in the population - 1.4% = 2 pq = 2 x 0.0071 x 0.9924 = 0.014 = 1.4%

Solving problems on the Hardy-Weinberg law 4. Alkaptonuria is inherited as an autosomal recessive trait. The disease occurs with a frequency of 1:1000. Calculate the number of heterozygotes in the population. Given: A - normal a - alkaptonuria Alc 1 normal Frequency 2 рq - ? = (p + q) 2 = p pq + q 2 = 1 p = 1 - 0.01 = 0.99 q2q2 = q = = 0.01 Answer: number of heterozygotes in the population - 1.9% = 2 pq = 2 x 0.01 x 0.99 = 0.0198 = 1.9%

Solving problems on the Hardy-Weinberg law 5. Congenital hip dislocation is inherited as dominant with an average penetrance of 25%. The disease occurs with a frequency of 6: Determine the number of homozygous individuals for the recessive gene. (p + q) 2 \u003d p pq + q 2 \u003d 1 Given: A - dislocation a - norm A 6 a Penetrance 25% q 2 -? \u003d p pq \u003d Answer: the number of homozygotes a - 9976 individuals \u003d q 2 \u003d \u003d 9976 penetrance is 25% or ¼, then there will be 4 times more carriers of the gene, therefore р рq =

Solving problems on the Hardy-Weinberg law 6. Gout occurs in 2% of people and is caused by an autosomal dominant gene. In women, gout does not appear; in men, the penetrance is 20%. Determine the genotypic structure of the population according to the analyzed trait. (p + q) 2 = p pq + q 2 = 1 Given: A - gout a - norm Penetrance - 2%: - no - 20% Genet. population structure? 2% get sick, but only, and there are 5 times more carriers of the gene among them, because penetrance 20% (100% : 20% = 5) (p + q) 2 = p pq + q 2 = 1 10% carriers of the disease gene, 10% + 10% who carry the gene but do not get sick 20% carriers of the gout gene

Solving problems on the Hardy-Weinberg law 7. The structure of the population according to the blood system MN in % among: Population of the CIS Europeans Papuans MM - ,1 MN - ,6 NN - Determine the frequency of genes L N and LM in the specified populations.

gene pool

In order to understand what is at stake, you need to know the definitions.

The gene pool is the totality of the genotypes of all individuals in a population.

A population is a group of single-species organisms that occupy a certain area of the territory within the range, interbreed freely among themselves and partially or completely isolated from other populations. population gene pool mutation

The mutation process is the source of hereditary variability.

Genetic balance in populations

The frequency of occurrence of various alleles in a population is determined by the frequency of mutations, selection pressure, and sometimes by the exchange of hereditary information with other populations as a result of migrations of individuals. With relatively constant conditions and a high population size, all of these processes lead to a state of relative equilibrium. As a result, the gene pool of such populations becomes balanced; a genetic balance is established in it, or the constancy of the frequencies of occurrence of various alleles.

Causes of genetic imbalance

The example given earlier with the action of insecticides suggests that the action of natural selection leads to directed changes in the gene pool of a population - an increase in the frequencies of "useful" genes. Microevolutionary changes are taking place. However, changes in the gene pool can also be of an undirected, random nature. Most often they are associated with fluctuations in the number of natural populations or with the spatial isolation of a part of the organisms of a given population.

Changes in the gene pool can be directed and undirected, random changes can occur due to various reasons. One of the significant reasons leading to a change in the frequencies of alleles and genotypes in populations is the flow of genes, or the migration of individuals (seeds, spores, pollen). The higher the intensity of migration and the greater the difference in allele frequencies, the greater its impact on population equilibrium and genotypic frequencies. Infrequently, populations are completely closed systems. Usually between them there is an exchange of genes, the magnitude of which depends on spatial proximity and other factors.

The cessation of gene flow from population to population can be the result of various events and have different evolutionary consequences. In such cases, there are polishing mechanisms associated with a sharp restriction or complete cessation of crossing with representatives of different populations and species.

An example of an insulating barrier is isolation, lowered with changes in the landscape: the formation of barriers in the form of rivers, mountain ranges, forests, etc. As a result, free interbreeding of land individuals is difficult due to water barriers, and individuals living in water - due to land barriers. The uplands isolate the flat areas, while the plains isolate the mountain populations.

Sharp fluctuations in populations, whatever they may be caused, change the frequency of alleles in the gene pool of populations. When unfavorable conditions are created and the population is reduced due to the death of individuals, the loss of some genes, especially rare ones, may occur. In general, the smaller the population, the higher the probability of losing rare genes, the greater the impact on the composition; gene pool random factors. Periodic fluctuations in numbers are characteristic of almost all organisms. These fluctuations change the frequency of genes in populations that replace each other.

An example is some insects; only a small number of them survive the winter. This small fraction gives rise to a new summer population, its gene pool is often different from the gene pool of the population that existed a year ago.

Random, non-directional change in allele frequencies in small populations N.P. Dubinin and D.D. Romashov was called genetic-automatic processes. Independently of them, the American S. Wright and the Englishman R. Fisher called this phenomenon genetic drift.

What are the main provisions of the teachings of Ch. Darwin?

1. Organisms are changeable. It is impossible to find two completely identical rabbits, wolves, lizards or other animals or plants belonging to the same species.

2. Differences between organisms are, at least in part, inherited.

3. Theoretically, under favorable conditions, any organisms can multiply so much that they are able to fill the Earth, but this does not happen, since many individuals die without having time to produce offspring.

4. Those organisms that have beneficial properties are more likely to survive than others. Survivors pass these properties on to their offspring. Consequently, these properties are fixed in a series of subsequent generations.

Evidence for Darwin's theory

On what facts did Darwin base the evidence for his theory?

The facts on which Darwin based his evidence for his theory are:

1) island plants and animals differ sharply from closely related species on the continent;

2) related species on different islands differ in appearance, body size, and life habits against the background of diverse habitat conditions;

3) fossil remains of the giant sloth and armadillo were found, significantly larger than their relatives, still inhabiting Central and South America;

4) the preservation of marsupials and oviparous precisely in Australia, where they found themselves in isolation, and died out in other places on the globe;

5) differences between different breeds of the same kind of domesticated animals, which are sometimes even more significant than between different types of wild animals;

6) each organism is able to produce more offspring than it can survive, and only a limited number of them survive and leave their offspring.

Struggle for existence

What facts allow us to talk about the struggle for existence? How does this struggle manifest itself in nature?

Living organisms tend to multiply exponentially and theoretically any organism can fill the Earth very quickly.

In fact, this never happens, because the resources of life are limited and go to only a few - those who can win the struggle for life, or the struggle for existence.

The intraspecific struggle for existence is manifested in different species, primarily in competition for food resources and a sexual partner. As a rule, a direct collision of individuals is prevented by various adaptations, among which marks should be distinguished that designate an individual area: the singing of songbirds, the leaving of odorous secretions, etc. Violation of the boundaries of an individual area is often accompanied by fights. Less common is direct interaction, such as cannibalism.

Variability

What is variability in organisms?

Variability is the property of organisms to acquire new features that distinguish them from other organisms of the same species. Variability affects all the properties of organisms: structural features, color, physiology, behavioral features, etc.

Variability forms

What kinds of variability do you know?

There are two main forms of variability - non-hereditary and hereditary (genetic).

Population hereditary variability

What is population genetic variation? Why does the gene pool of a population change over time?

The hereditary variability of a population is the most important property of this supraorganismal system, which lies in the fact that the population as a whole is capable of acquiring traits that distinguish it from other populations of the same species.

The gene pool is the sum of all genotypes present in a population. It is the most important indicator of the genetic composition of the entire population. The gene pool of a population changes over time due to the variability of genotypes and as a result of natural selection.

Adaptive changes in the gene pool

What facts can serve as proof of the adaptive (adaptive) nature of changes in the gene pool?

One example proving the adaptive nature of changes in the gene pool of a population is the so-called industrial mechanism in the birch moth.

The color of the wings of this butterfly imitates the color of the birch bark, on which these dusky butterflies spend daylight hours.

In populations living in industrial areas, over time, the previously extremely rare dark butterflies began to dominate, while white ones, on the contrary, became rare. In the gene pools of these populations, the frequency of alleles that determine the corresponding protective coloration has changed.

Evolutionary changes in the gene pool

What changes in the gene pool allow us to draw a conclusion about the evolutionary changes taking place in the population?

genetic balance

What is genetic balance? Under what conditions is it possible?

Factors of violation of genetic balance

What factors cause genetic imbalance in conditions when natural selection does not act?