Subject: Biology
Topic: "The evolutionary meaning of mutations"
The purpose of the lesson: to create conditions for assimilation of the concept of mutation, to consider the evolutionary role of mutations.
Lesson Objectives:
Educational:patriotic education on the example of domestic scientists who have studied the mutational process;
Developing:formation of skills and abilities of independent work, lay the foundations for the study of genetics;
Educational: to consider the essence of the mutational process, to identify its role in evolution.
Lesson type: Combined.
Method of conducting: conversation, explanation, independent work group work.
During the classes:
Organizing time ... Greeting. Preparing the audience for work. Checking for the presence of students.
Student assessment and goal setting .
Teacher:now we will do testwith which we will learn what we will learn in today's lesson. (students begin the test). Appendix 1.
The teacher together with the students, using a correctly completed test, communicate the topic of the lesson and the purpose of the lesson.
Presentation of new material.
Teacher:We write down the topic of the lesson.
Remember, evolution is divided into two types:
Evolution
Microevolution Macroevolution
What is the definition of microevolution? (speciation).
The teacher conducts a frontal survey to guide students to independent study of this topic:
The unit of heredity is ...?
Where is the chromosome located?
Using the drawing in the presentation and discussions with the teacher, the students themselves formulate the definition of the term gene. (A gene is a section of a DNA molecule that contains hereditary information.)
Teacher:a living organism and each of its cells are always exposed to different influences environment... Exposure to the external environment can cause disturbances in the process of cell division and "errors" in copying genes and chromosomes. What do you think such "mistakes" lead to? (Mutations)
Mutation - changes in the hereditary apparatus of a cell, affecting whole cells or their parts.
Teacher: Question to the class: What is the role of mutations in the evolutionary process? To answer this question, we will consider in more detail the mutation process. What are mutations?
Beneficial mutations: mutations that lead to increased resistance of the organism (resistance of cockroaches to pesticides). Harmful mutations: deafness, color blindness. Neutral mutations: mutations do not affect the viability of the organism (eye color, blood type).
Mutation as a factor in evolution.
Teacher:The study of natural mutations was carried out by our domestic scientist S.S. Chetverikov. Most mutations are harmful, but rare beneficial mutations are the starting material for evolution.
The resulting recessive mutations go into a heterozygous state and are invisible. But each species (population), like a sponge, is saturated with these mutations. Thus, there is latent variability. Since genetic diversity is the result of evolution, mutation is necessary for evolutionary progress.
Processes that change the genetic structure of a population.
It is known that in different populations of the same species, the frequency of mutant genes is not the same:
Migration;
"Waves of Population";
Insulation.
Students need to divide into groups and plan to speak to the class about the chosen process that changes the genetic structure of the population.
Summing up (reflection)
Today in class I ...
The most useful interesting thing for me was ...
I met with difficulty in ...
Teacher:How do you rate today's classroom work?
Consolidation of the studied material (lesson conclusion):
What role do mutations play in evolution?
Homework. Fill in the table (Appendix 3) and answer the questions on p. 58.
Appendix 1.
Test on the topic: “A species is an evolutionary unit. Its criteria and structure "
Which statement is most correct:
2) Which of the listed organisms cannot evolve?
Y) a female bee.
I) the population of bees.
T) A flock of pigeons.
3) The criterion that characterizes a certain area occupied by a species in nature is ...
K) Environmental criterion
B) Morphological criterion
T). Geographic criterion
D) Physiological criterion
4) A set of geographically and ecologically close populations capable of interbreeding with each other, having common morpho-physiological characteristics, is ...
A) View
H) Specimen
C) Population
W) Class
5) The degree of mobility of individuals is expressed by the distance the animal can move - this distance is called ...
C) The radius of individual activity
G) Migration
E) Insulation
I) There is no right answer
6) For species living in Lake Baikal, the range is limited to this lake - this is an example of ... criterion
K) Environmental
T) Morphological
I) Geographic
D) Physiological
7) .Criticity of a species, which includes a combination of environmental factors that make up the immediate habitat of a species, is ... criterion
I) Environmental
Y) Geographic
I) Morphological
D) There is no right answer
Throughout the ages, mankind has tried to find answers to the questions: How did this colossal diversity form? Why is each species optimally adapted to the conditions of its habitat? How do some species differ from others? Why do some species flourish, while others die out and disappear from the face of the Earth?
1. Elementary unit of evolution Population 2. Elementary evolutionary material Mutations - genotypic diversity in populations 3. Elementary evolutionary phenomenon Long-term and directed change of the gene pool 4. Elementary evolutionary factors Hereditary variability, struggle for existence, natural selection - guiding factor 5. Elementary object of selection Separate individual with a certain phenotype
S.S. Chetverikov Populations, like a sponge, absorb recessive mutations, while remaining phenotypically homogeneous. The existence of such an open reserve of hereditary variability creates an opportunity for evolutionary transformations of the population under the influence of natural selection... He studied natural mutations, changes in the hereditary properties of the organism. Introduced significant contribution in the development of population genetics.
The mutational process is a constantly acting source of hereditary variability. Genes mutate at a certain frequency. During sexual reproduction, mutations can spread widely in populations. Most organisms are heterozygous for many genes, that is, in its cells, homologous chromosomes carry different forms of the same gene. Heterozygous organisms are better adapted than homozygous ones.
The mutational process is the source of the reserve of hereditary variability of populations. By maintaining a high degree of genetic diversity in populations, it creates the basis for the action of natural selection. In different populations of the same species, the frequency of mutant genes is not the same. There are no populations with exactly the same frequency of occurrence of mutant characters. These differences may be due to the fact that populations live in different environmental conditions. A directed change in the frequency of genes in populations is due to the action of natural selection.
Waves of life fluctuations in the number of individuals in a population. The term was introduced by the Russian biologist S.S.Chetverikov in 1915. Such fluctuations in abundance can be seasonal or non-seasonal, recurring at various intervals; usually they are the longer, the longer the development cycle of organisms. Subsequently, the term was replaced by the concept of population waves (one of the 4 elementary evolutionary factors is the mutation process, population waves, isolation and natural selection). The main significance is reduced to random changes in the concentrations of various mutations contained in populations, as well as to a weakening of the selection pressure with an increase and its strengthening with a decrease in the number of individuals in a population. The term sometimes refers to the stages of development of the flora and fauna, roughly corresponding to the change in geological cycles.
Evolutionary factors - factors causing the evolution of populations. "Waves of life" and "gene drift", as a rule, accompany the evolutionary process of each population when it comes to a long process (period of time). However, the historical development of the organic world is theoretically possible without them, that is, only on the basis of variability, heredity, the struggle for existence and natural selection.
Can all the causes of the death of organisms be considered natural selection? Natural selection is not the only cause of the death of organisms. The death of an animal may be a consequence random event (forest fire, flood or other natural disaster, which leaves no chance of survival).
Evolutionary factors Guiding the evolutionary process Non-guiding the evolutionary process Natural selection (against the background of the struggle for existence) -Hereditary variability. - Gene drift. - Waves of life. - Insulation. Acts in a population, changing its gene pool Possible result: the emergence of new populations, subspecies, species (speciation)
The set of evolutionary processes occurring in populations of a species and leading to a change in the gene pools of these populations and the formation of new subspecies, species, is called microevolution. Evolution at the level of systematic units above a species, taking millions of years and inaccessible to direct study, is called macroevolution. These two processes are one. Homework: Page Give examples of aromorphoses, idioadaptation and degeneration. Repeat definitions of species, population, evolution, macroevolution, microevolution.
In this lesson, you will learn about how mutations are related to the evolutionary process. Remember or learn what mutations are. What is their significance? How are cancers related to evolution? IN this lesson you will become familiar with two types of hereditary variation (combinative and mutational) and consider mutations as a constant source of hereditary variation. You will learn about the likelihood of mutations, their consequences for organisms, as well as how mutations spread in a population. The principles of maintaining the genetic diversity of species through heterozygous individuals will be considered.
Topic: Evolutionary teaching
Lesson: The Evolutionary Role of Mutation
1. Hereditary variability
One of the main driving forces of evolution according to Charles Darwin is hereditary variability. It is more or less obvious that Charles Darwin studied hereditary variability without possessing modern genetic concepts. Today it is known that hereditary variation is the result of the sexual process and the mutational process (see Scheme 1).
2. Mutation process
The mutational process is one of the main sources of hereditary variation.
Genes mutate at a certain frequency.
According to modern concepts, the probability of a mutation in a particular pair of nucleotides is about 10-8. Therefore, if the human genome consists of about 3 billion nucleotides, then each human descendant carries about 30 mutations that his parents did not have.
Mutations are widespread in populations. Not all mutations affect genes - most mutations accumulate in non-coding sequences.
According to their consequences for the organism, mutations can be conditionally divided into harmful, beneficial and neutral (see Scheme 2).
Beneficial mutations are extremely rare. It can be assumed that organisms homozygous for deleterious mutations will be permanently excluded from the population. The frequency of the mutant allele will decrease, respectively, the proportion of heterozygotes will also decrease. But, in fact, this does not happen in populations, because heterozygous organisms, as a rule, turn out to be more adapted to environmental conditions.
Let us consider this phenomenon using the example of the populations of the Birch moth butterfly. It seems that light-colored butterflies, homozygous for the recessive allele, living in the forest with dark trunks, should be completely destroyed by enemies. The only form under these conditions should be dark-colored butterflies homozygous for the dominant allele. But in fact, white butterflies are constantly found in the smoky forests of southern England. Why? Recessive alleles in a population persist in heterozygous organisms (see Fig. 3).
Figure: 3. Two forms of birch moth on a dark tree trunk: easily distinguishable white on top and dark barely noticeable under it
Thus, although most mutations in genes are harmful, they are still present in the population. It is worth noting that mutations that are harmful in one case may be beneficial in another.
For example, insect mutations that lead to the birth of wingless individuals are certainly harmful, and such individuals lose to their winged rivals. But when these insects hit the seashore or mountain passes, where very strong winds blow, wingless individuals gain an advantage over winged insects.
Thus, the mutational process creates a reserve for hereditary variability; by increasing the genetic diversity of a population, it creates the basis for natural selection.
2.1. Mutation rate
The rate of mutation is generally constant for each taxon, but it differs in different kingdoms of living organisms. This rate of occurrence of mutations (mutagenesis) is maximum in microorganisms and viruses.
The mutation rate can sometimes increase in leaps and bounds. This usually happens when the body gets into adverse environmental conditions. In this case, the mutation rate can be accelerated by more than an order of magnitude.
2.2. Mutation rate
Harmful mutations in diploid organisms usually manifest themselves only in the homozygous state.
In large populations, such mutations are less often manifested than in small groups of individuals. With closely related crosses (for example, between brothers and sisters), mutant alleles are more often homozygous and appear in the phenotype.
Homework
1. What are mutations? How do they arise? What are they like?
2. What is elimination? How is the elimination of harmful mutations carried out?
3. What is the relative fitness of an organism? How is it expressed?
4. What factors are called mutagenic? What are their benefits and harms?
5. What is the rate at which mutations occur?
6. Discuss with friends the relative fitness of living organisms. What useful practical conclusions can be drawn from knowledge of the relative fitness of organisms?
1. Wikipedia.
2. Wikipedia.
3. Wikipedia.
List of references
1. Kamensky A. A., Kriksunov E. A., Pasechnik V. V. General biology 10-11 class Bustard, 2005.
2. Belyaev DK Biology 10-11 grade. General biology. A basic level of... - 11th ed., Stereotype. - M .: Education, 2012 .-- 304 p.
3. Biology Grade 11. General biology. Profile level / V. B. Zakharov, S. G. Mamontov, N. I. Sonin and others - 5th ed., Stereotype. - Bustard, 2010 .-- 388 p.
4. Agafonova IB, Zakharova ET, Sivoglazov VI Biology 10-11 grade. General biology. A basic level of. - 6th ed., Add. - Bustard, 2010 .-- 384 p.
Through the study of genetic processes in the population of living organisms, evolutionary theory got a new impetus and further development... The contribution of the Russian scientist S. Chetverikov to population genetics is great. He drew attention to the saturation of natural populations recessive mutations, as well as fluctuations in the frequency of genes in populations, depending on the action of environmental factors and substantiated the position that these two phenomena are the key to understanding the processes of evolution.
Indeed, the mutational process is a constantly acting source of hereditary variability. Genes mutate at a certain frequency. It is estimated that, on average, one gamete out of 10 thousand - 1 million gametes carries a newly arisen mutation at a certain locus. Since many gametes mutate at the same time, 10-15% of gametes carry one or another mutational allele. Therefore, natural populations are saturated with a wide variety of mutations. Due to combinative variability, mutations can spread widely in populations. Most organisms are heterozygous for many genes. It could be assumed that as a result of sexual reproduction, homozygous organisms will be constantly allocated among the offspring, and the proportion of heterozygotes should steadily decrease. However, this does not happen. The fact is that in the overwhelming majority of cases, heterozygous organisms are better adapted than homozygous ones.
In the example with a butterfly, a birch moth, it would seem, light-colored butterflies homozygous for the recessive allele (aa), living in a forest with dark birch trunks, must quickly destroy enemies and the only form in these habitats should be dark-colored butterflies homozygous for the dominant allele (AA). But for a long time in the smoky birch forests of the South of England, light butterflies of the birch moth are constantly found. It turned out that caterpillars homozygous for the dominant allele poorly assimilate birch leaves covered with smoke and soot, and heterozygous caterpillars grow much better on this food. Consequently, the greater biochemical flexibility of heterozygous organisms leads to their better survival, and selection acts in favor of heterozygotes.
Thus, although most mutations under these specific conditions are harmful and in a homozygous state, mutations, as a rule, reduce the viability of individuals, they persist in populations due to selection in favor of heterozygotes.
To understand evolutionary transformations, it is important to remember that mutations that are harmful in some conditions can increase viability in other environmental conditions. In addition to the above examples, you can point to the following. A mutation that causes underdevelopment or complete absence of wings in insects is undoubtedly harmful under normal conditions and wingless individuals are quickly replaced by normal ones. But in the oceanic expanses and mountain passes, where strong winds blow, such insects have an advantage over individuals with normally developed wings.
Thus, the mutational process is the source of the reserve of hereditary variability of populations. By maintaining a high degree of genetic diversity in populations, it creates the basis for the action of natural selection.
Genetic processes in populations
In different populations of the same species, the frequency of mutational genes is not the same. There are practically no two populations with a perfect frequency of occurrence of mutational traits. These differences may be due to the fact that populations live in different environmental conditions. A directed change in the frequency of genes in populations is due to the action of natural selection. But even closely located, neighboring populations can differ from each other as significantly as far-away ones. This is explained by the fact that in populations a number of processes lead to an undirected random change in the frequency of genes, or, in other words, their genetic structure.
For example, during the migration of animals or plants, a small part of the original population appears in the new habitat. The gene pool of the newly formed population is inevitably smaller than the gene pool of the parental population, and the gene frequency in it will differ significantly from the gene frequency of the original population. Genes, previously rare, spread rapidly through sexual reproduction among a new population. At the same time, widespread genes may be absent if they were not present in the genotype of the founders of the new population.
Another example. Natural disasters - forest or steppe fires, floods, etc. - cause massive, inevitable death of living organisms, especially sedentary forms: plants, fungi, molluscs, amphibians, etc. Individuals that have escaped death survive by pure chance. In the population that survived the catastrophe, there is a decrease in numbers. In this case, the allele frequencies will be different than in the original population. Following the decline in numbers, mass reproduction begins, the beginning of which is given by the remaining, small group. The genetic makeup of this group determines the genetic structure of the entire population during its heyday. In this case, some mutations may completely disappear, and the concentration of others may accidentally increase sharply.
In the biocenosis, periodic fluctuations in the population size are often observed, associated with relationships of the "predator - prey" type. Enhanced reproduction of predator hunting objects based on an increase in food resources leads, in turn, to enhanced reproduction of predators. The increase in the number of predators causes the mass destruction of their prey. Lack of food resources causes a decrease in the number of predators and restoration of the size of prey populations. These fluctuations in numbers are called population waves. They change the frequency of genes in populations, which is their evolutionary significance.
Limitation of gene exchange between them, due to spatial isolation, also leads to changes in the frequency of genes in populations. Rivers serve as barriers to terrestrial species, mountains and hills isolate the lowland populations. Each of the isolated populations has specific characteristics associated with living conditions. An important consequence of isolation is closely related crossbreeding - inbreeding. Due to inbreeding, recessive alleles, spreading in the population, appear in a homozygous state, which reduces the viability of organisms. In human populations, isolates with high degree inbreeding are found in mountainous areas and on islands. The isolation of certain groups of the population for caste, religious, racial and other reasons also retained its importance.
The evolutionary significance of different forms of isolation is that it reinforces and reinforces genetic differences between populations, and that divided parts of a population or species are subjected to unequal selection pressures.
Thus, changes in the frequency of genes caused by various environmental factors serve as the basis for the emergence of differences between populations and subsequently determine their transformation into new species. Therefore, changes in populations during natural selection are called microevolution.
test questions
1. Work of S. Chetverikov in the field of population genetics.
2. The evolutionary role of mutations.
3. The mutational process is the source of the reserve of hereditary variability of populations.
4. Changes in the frequency of genes in the population.
5. What is microevolution?
A mutation is called persistent changes in the genotype that occur due to the influence of external and internal factors. The originator of the term is Hugo de Vries, a Dutch botanist and geneticist. The process when mutations appear is called mutagenesis. In today's article, we will touch upon the topic of mutation and talk about the role of mutation in the evolutionary process.
Causes of the phenomenon
It is characterized by two qualities - spontaneity and induction. The appearance is characterized by spontaneity and occurs at any stage of the body's development. As for the environment, it should be natural.
An induced type of mutation is a hereditary change in the genome that occurs as a result of exposure to various mutagens. Organisms are placed either in artificially created (experimental) or unfavorable environmental conditions.
Living cells perceive mutagenesis as a natural process for them. The main processes responsible for mutation include: replication and impaired DNA repair, transcriptional process, and genetic recombination.
Mutagenesis and its models
In explaining and understanding the nature and mechanisms of the appearance of mutations, special scientific approaches... Polymerase changes are based on the theory of a direct and only dependence of mutations with DNA polymer errors. In tattoo models of mutagenesis, proposed by two well-known biologists, the idea was first raised that the main layer of mutations lies in the possibility of DNA bases to be located in different tattoo forms.
Early classification of mutations
Geneticist Möller created a classification of mutations based on the types of changes in the functioning of genes. As a result, the following types appeared:
- Amorphous. During mutation, a gene loses almost all of its functions. An example of a mutation is changes in Drosophila.
- Hypomorphic. The changed alleles continue to act in the same scenario as the wild ones. The synthesis of the protein product is carried out in smaller quantities.
- Antimorphic. Change in the mutant trait. Examples of mutation are some corn kernels - they turn purple instead of purple.
- Nonomorphic.
Late classification of mutations
In modern scientific reference books there is a mention of a formal classification, which is based on the changes taking place in various structures. Based on this division, the following mutations are distinguished:
- Genomic.
- Chromosomal.
- Genetic.
Changes in chromosomes are associated with genomic mutations, the total number of which does not correspond to the halogen set.
Chromosomal mutations are credited with rearranging individual chromosomes in large numbers. In this case, the genetic material loses some part or, conversely, doubles it.
As for the gene mutation, it only slightly changes the DNA structure of the gene, unlike other species, but its occurrence occurs much more often.
Within a gene species, another subspecies is distinguished, called a point mutation. In it, one nitrogenous base is replaced by another.
It also happens that the harmfulness of mutations is gradually replaced by usefulness. The impetus for such changes is the constantly changing conditions of the existence of organisms. So what role do mutations play?
Take natural selection, a well-known evolutionary process that depends a lot on variability. Let us consider the evolutionary role of mutation using the example of melanist mutants (individuals with a dark color), which were discovered by English scientists of the 14th century when studying birch moths. In addition to the typically light colored butterflies, other individuals were found whose color was much darker. The reason for this strong difference was the mutated gene.
The fact is that the usual habitat for such butterflies is trees, on the trunks of which lichen grows abundantly. Reigning in early years the industrial revolution, together with heavy pollution of the atmospheric layers, led to the death of lichens. Soot appeared on the once light trunks, which interfered with natural camouflage.All this led to the fact that individuals whose habitat was industrial areas changed the color of their morph from light to dark. This evolutionary role of the mutation helped many butterflies survive, while their not very successful light-colored relatives fell prey to attacks by birds of prey.
Similar changes are occurring in a wide variety of species around the world. The emergence of such useful traits, which are the basis of the evolutionary role of mutation, leads to the fact that natural selection gives rise to new subspecies and species among living organisms. Mutation is happening all the time, because it is a natural ability of our genes.
For more information on mutation, see biology textbooks and specialist scientific literature.