The evolutionary role of mutations
Mutation
mutagens
Genotype
allele (allele homozygote heterozygote(Ah).
The evolutionary role of mutations
The body and each of its cells are continuously exposed to various environmental influences, which can cause disturbances in the process of cell division and “errors” in the copying of genes and chromosomes, i.e. mutation.
Mutation- a change in the hereditary apparatus of a cell, affecting entire chromosomes or parts thereof.
The study of natural mutations was carried out by the domestic scientist S.S. Chetverikov and the Dutch botanist De Vries.
Mutation is a continuous, random process, but not without cause!
The influences that cause mutations are called mutagens. The main mutagens are: all types of radiation, chemicals, viruses, bacteria, excessive high or low temperature, etc.
Mutations are: harmful, neutral and harmful. The same mutation can change its meaning under changing conditions. Most mutations are harmful, but rare beneficial mutations are the starting material for evolution.
All organisms in their natural state are characterized by free crossing - a stabilizing apparatus of genotypes in a population. ( Genotype - a set of genes of an organism).
A gene is a section of a DNA molecule containing hereditary information. The gene has two allele (allele – specific state of the gene): dominant gene – A, recessive gene – a. When two cells merge, a zygote is formed; if it has two identical alleles of a gene, then it is called homozygote(AA, aa), if different alleles – heterozygote(Ah).
Emerging recessive mutations become heterozygous and are invisible. But each species (population), like a sponge, is saturated with such mutations. Thus, hidden variability occurs.
Mutation frequency 10 -4, 10 -8.
Each organism has a large number of genes, therefore the probability of occurrence of a mutation is greater, the number of individuals in the population is large. Thus, we can say that mutation is a common phenomenon.
Since genetic diversity is a result of evolution, mutation is necessary for the evolutionary process.
The frequency of mutations depends on: natural disasters (some mutations disappear, while the concentration of others increases); migration (gene frequency changes - differs from the original); “waves of numbers”, isolation.
Changing the directions of natural selection in accordance with the new conditions of the struggle for existence
Selection of individuals, inheritance. changes in which allow them to develop new territories or habitats
Geographic speciation
Ecological speciation
Settlement in a new territory
Development of new ecological niches within the old range
Geographic isolation between populations
The emergence of subspecies
Biological isolation
The emergence of new species
Selection under new environmental conditions
Selection under new environmental conditions
Biological isolation
The emergence of subspecies
The emergence of new species
Sequence of events during speciation
Change in habitat or position of a species (population) in it
Intensification of the struggle for existence between individuals
Lesson script on the topic
"The evolutionary role of mutations"
Date: 10/14/2014
Subject: Biology
The topic of the lesson is “the evolutionary role of mutations”;
Textbook: Mamontov S.G., Sonin N.I. "Biology. General laws" 9th grade: Bustard, 2006.
The purpose of the lesson: create conditions for mastering the concept of mutation, consider the evolutionary role of mutations.
Lesson objectives:
Educational: patriotic education using the example of domestic scientists who have studied the mutation process;
Developmental: formation of skills and abilities for independent work, laying the foundations for the study of genetics;
Educational: consider the essence of the mutation process, identify its role in evolution.
Lesson type: Combined.
Method of implementation: conversation, explanation, independent work, group work.
During the classes:
Organizing time . Greetings. Preparing the audience for work. Checking the availability of students.
Testing students' knowledge and goal setting .
Teacher: Now we will complete a test task, with the help of which we will find out what we will study in today's lesson. (students begin to take the test). Annex 1.
The teacher, together with the students, using a correctly completed test, communicate the topic of the lesson and the purpose of the lesson.
Question number | |||||||
Presentation of new material.
Teacher: We write down the topic of the lesson: The evolutionary role of mutations.
Let us remember that evolution is divided into two types:
Evolution
Microevolution Macroevolution
Define the concept of microevolution? (speciation).
The teacher conducts a frontal survey to direct students to independently study this topic:
The unit of heredity is...?
Where is the chromosome located?
Using a drawing on the presentation and reasoning together with the teacher, students themselves formulate a definition of the term gene. (A gene is a section of a DNA molecule containing hereditary information.)
Teacher: a living organism and each of its cells are always exposed to various environmental influences. Exposure to the external environment can cause disturbances in the process of cell division and “errors” in the copying of genes and chromosomes. What do you think these “mistakes” lead to? (Mutations)
Mutation is a change in the hereditary apparatus of a cell, affecting whole cells or parts thereof.
Teacher: Question to the class: What is the role of mutations in the evolutionary process? To answer this question, we will look at the mutation process in more detail. What are the types of mutations?
Beneficial mutations: mutations that lead to increased resistance of the body (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).
Evolution is the process by which new forms of life arise from previously existing ones: flowering plants from ferns and mosses, birds and mammals from reptiles, humans from ape-like ancestors.
Evolution continues to this day, but from the point of view of evolutionary time scales, a human life is such a brief moment that a person is only rarely able to directly observe evolution. For example, we are witnessing the transformation of harmless bacteria into virulent ones or the displacement of lighter varieties by dark-colored butterflies in industrial areas.
The adaptation of each type of organism to its specific environment and way of life has always aroused the surprise and admiration of natural scientists. To achieve such amazing adaptability, nature works in much the same way as man does in breeding hardy sheep for mountain regions or disease-resistant potato varieties. The livestock breeder and plant breeder select individuals that are well adapted to the conditions in which these plants or animals will have to live. They reject those who are less fit. They often create new varieties by crossing existing lines and selecting from their offspring those individuals that combine the beneficial characteristics of both lines, such as the high yield of one variety of wheat and the frost resistance of another, or the silver coloring of a chinchilla rabbit with the soft fur of the river breed.
Evolution also works through crossing and selection. Its material is mutated genes present in all species. With each act of sexual reproduction, new combinations of genes arise. Individuals carrying different combinations of genes compete with each other in the struggle for existence. The fitter ones leave more offspring, and eventually the better combinations crowd out the worse ones. Even a relatively small number of mutated genes provides a huge reservoir of potential genetic variability. If humanity as a whole carried only 1,000 mutated genes, which is certainly a gross underestimation, the number of possible combinations of these genes would greatly exceed the number of all people living on earth. There are no two people, with the exception of identical twins (see article on that), who would be completely identical in their genetic constitution.
Despite the fact that evolution uses already existing genes for its immediate purposes, the primary raw material is mutations, as a result of which new genes appear. Mutation is thus one of the greatest driving forces of evolution, and since the evolutionary process continues, mutation is still necessary for the preservation and progress of life on Earth.
However, most new mutations are harmful or even lethal. What explains this? The reason is that every existing organism is the result of a long evolution, during which it has so finely adapted itself to the demands of its mode of life that any change in its organization is more likely to be a change for the worse than for the better. Let's imagine: a man broke some wheel in his watch and the watchmaker to whom he took the watch selects a new wheel at random from a whole pile of parts of all sizes and varieties. It is very likely that after this the watch will run poorly, and perhaps even be completely damaged. The most complex clock is much simpler than the most primitive organism. Dozens of interconnected wheels are needed to keep the clock moving; thousands of interconnected physiological processes are necessary for an organism to develop and survive. A mutation, replacing one gene with another, changes one of these processes by chance. It is not surprising that most mutations disrupt the harmony of the body, and many even lead to death.
The extent to which a particular mutation will be harmful will depend on lifestyle and the organism's environment. For a green plant, whose existence depends on the chemical activity of the chlorophyll it contains, a mutation that causes albinism will be lethal. Animals living in caves can live without pigment, and therefore the mutation leading to albinism can spread among them. In arctic conditions, selection favors white mutants.
When environmental conditions change, mutants, who were losers under the old conditions, come forward and can even displace their non-mutated ancestors. The small water flea Daphnia is a common inhabitant of our ponds and various bodies of water. It develops well at a temperature of 20° C and dies if the temperature rises to approximately 27° C. In laboratory conditions, a mutant has arisen that requires a temperature of 25 to 30° C for its existence. Under modern climatic conditions in England, mutant individuals could not exist. Let us imagine, however, that the temperature increased by 7-8 ° C. In this case, mutants would be the only individuals capable of surviving, and they would lay the foundation of a new line consisting entirely of mutants.
In the same way, mutant individuals acquire value when the species colonizes new territories or changes its lifestyle. In the course of evolution, life continuously explored new territories: seas, land, fresh waters, air, and penetrated into other organisms - plants and animals. When a person settles new lands, he needs men and women who can exchange a typewriter for a shovel and a gas stove for a stove made of stones. When life expands into new territories, it needs species that, because they have a large supply of mutated genes, are still sufficiently variable to select settlers into the new conditions. If the Ice Age were to return to our lands, the white birds, which are sometimes found among our wild species, would probably be the first successful inhabitants of the snow-covered regions.
Thus, from a species perspective, mutations are as harmful as they are necessary. Mutations are harmful as long as the conditions of existence remain unchanged, since living organisms, as a result of their evolution, adapt to their environment and way of life, and mutations are more likely to weaken or destroy than to improve this age-old adaptability. Mutations are necessary because the conditions of existence never remain unchanged for a long period of time. Gradually, over the years and centuries, the climate changes; rivers change their course; the mountains are smoothed out; Some food sources are depleted and new ones appear; predatory animals move from one area to another, and people in previously uninhabited corners of the Earth continuously create new living conditions for plants and animals. As a result, only species that will be able to meet each change in the environment with a new adaptation will survive, and these will be those species that have a sufficient supply of mutant genes. Thus, each species must maintain a balance between the requirement for maintaining a low mutation rate, dictated by present conditions, and the requirement for a significant accumulation of mutations, dictated by future prospects. A species that mutates too frequently will go extinct because many of its individuals will be weak, short-lived, or infertile. Species in which mutations occur too rarely may survive successfully for some time, but they will not survive when changing conditions require them to adapt for which they do not have the necessary genes.
So-called spontaneous mutation rate, i.e., the average frequency with which the genes of a given species mutate represents the resulting equilibrium between these conflicting requirements. The frequency of spontaneous mutation has been studied in only a few species. It ranges from one mutation for a given gene per 100 thousand germ cells to one mutation per 10 million cells. However, both higher and lower mutation frequencies are known. Some abnormalities in humans are caused by genes with a fairly high mutation rate. Thus, approximately 3 out of 100,000 human X chromosomes carry the new hemophilia mutation. If 800,000 children were born in England every year, half of them boys, and these children carried 1,200,000 X chromosomes (each boy one and each girl two), then it would turn out that every year 36 children would be born in England carrying one new gene hemophilia. All boys will be hemophiliacs, all girls will be outwardly normal “carriers”.
Some other human genes appear to mutate at even higher rates, but there is reason to believe that most human genes have a lower mutation rate, probably 1 in 100,000 gametes or less.
How does spontaneous mutation occur? This is apparently one of the most important problems of genetics, but it has so far only been partially resolved. We know that ionizing radiation causes mutations and that radiation exists both in the atmosphere and in the soil. There is no doubt that these naturally occurring radiations cause spontaneous mutations, but it has been calculated that their numbers are too small to account for only a fraction of the total number of mutations observed in nature. Using a number of chemicals, it was possible to obtain mutations in the laboratory. Some of them, such as mustard gas, are as effective as ionizing radiation. Others, with less genetic potency, occur naturally or are close to some naturally occurring compounds. Thus, it is very likely that mutagenic chemicals are partially responsible for the occurrence of spontaneous mutations. We also know that spontaneous mutations occur more often at high than at low temperatures. Physics teaches us that at high temperatures the molecules that make up matter move faster than at low temperatures. This makes it plausible that extremely rapid movement of molecules in the vicinity of a gene can cause a mutation in it. It is also very likely that a mutation can occur during the period when a gene, in preparation for division, forms next to itself a completely similar gene. This is a very complex process that can be compared to folding cubes into an exact copy of the design depicted on the lid of a box. If even one cube is missing or two cubes are swapped, the copy will be inaccurate. A gene may also not have all the parts needed to create its counterpart, or it may make a "mistake" in selecting and combining different parts. If once an inaccurate copy has been created, it will henceforth serve as a template for the creation of subsequent copies, and thus the new mutated gene will be propagated.
Numerous studies have been devoted to the effects of various mutagens. In what follows we will consider in more detail only one mutagen, namely ionizing radiation, since this source of mutability has become of paramount importance in the atomic age. At the same time, one cannot ignore the fact that an increasing number of chemicals are used as medicines, cosmetics, food additives, and also in production processes. It is possible that some of them may cause mutations and thus, like ionizing radiation, pose a danger.
Plans to test the genetic effects of drugs and other chemicals are widely discussed, and these plans are likely to come to fruition in the near future. However, it is not easy to draw definite conclusions from such experiments. While we can be sure that deeply penetrating ionizing radiation will cause mutations in all organisms, the situation is different with chemicals: they can have different effects on different organisms. For example, caffeine causes mutations in bacteria, but is completely ineffective in experiments on mice. Mice are much closer to humans than bacteria, so we might consider these results comforting and conclude that drinking large amounts of tea and coffee cannot harm our offspring, regardless of how it affects our own health. Although this conclusion seems quite reasonable, it cannot be completely certain. A cautionary note is that adding small amounts of formaldehyde to the food of Drosophila larvae causes mutations in males, but not in females. It is this lack of uniformity in the action of chemicals that makes it so difficult to draw conclusions about humans based on laboratory studies of mutations. Some conclusions must still be drawn if we want to avoid burdening humanity with unwanted mutations induced by chemicals.
We will not deal further with this issue and will limit our discussion to the mutagenic effect of X-rays. Different types of ionizing radiation do not act identically, but these differences are minor and are of interest more to theoretical geneticists than to non-geneticists who want to get an idea of the genetic danger that humanity will have to face in the future.
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In this lesson you will learn how mutations are related to the evolutionary process. Remember or find out 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 variability (combinative and mutational) and consider mutations as a constant source of hereditary variability. You will learn about the likelihood of mutations occurring, their consequences for organisms, as well as the ways in which mutations spread through a population. The principles of maintaining the genetic diversity of species thanks to heterozygous individuals will be considered.
Topic: Evolutionary teaching
Lesson: The Evolutionary Role of Mutations
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 having modern genetic concepts. Today it is known that hereditary variability is the result of the sexual process and the mutation process (see Scheme 1).
Bibliography
1. Kamensky A. A., Kriksunov E. A., Pasechnik V. V. General biology 10-11 grade Bustard, 2005.
2. Belyaev D.K. Biology 10-11 grade. General biology. A basic level of. - 11th ed., stereotype. - M.: Education, 2012. - 304 p.
3. Biology 11th grade. General biology. Profile level / V. B. Zakharov, S. G. Mamontov, N. I. Sonin and others - 5th ed., stereotype. - Bustard, 2010. - 388 p.
4. Agafonova I. B., Zakharova E. T., Sivoglazov V. I. Biology 10-11 grade. General biology. A basic level of. - 6th ed., add. - Bustard, 2010. - 384 p.
In all centuries, humanity has tried to find answers to the questions: How was this colossal diversity formed? Why is each species optimally adapted to its habitat conditions? How do some species differ from others? Why do some species thrive 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 in the gene pool 4. Elementary evolutionary factors Hereditary variability, struggle for existence, natural selection - directing factor 5. Elementary object of selection Separate an individual with a certain phenotype
S.S. Chetverik Populations, like a sponge, absorb recessive mutations while remaining phenotypically homogeneous. The existence of such an open reserve of hereditary variability creates the opportunity for evolutionary transformations of the population under the influence of natural selection. He studied natural mutations and changes in the hereditary properties of the body. Made a significant contribution to the development of population genetics.
The mutation process is a constantly operating source of hereditary variability. Genes mutate at a certain frequency. During sexual reproduction, mutations can spread widely throughout populations. Most organisms are heterozygous for many genes, that is, in their cells homologous chromosomes carry different forms of the same gene. Heterozygous organisms are better adapted than homozygous ones.
The mutation process is a source of reserve of hereditary variability of populations. By maintaining a high degree of genetic diversity in populations, it provides the basis for natural selection to operate. 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 traits. These differences may be due to the fact that populations live in different environmental conditions. Directed changes in gene frequency in populations are 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 numbers may be seasonal or non-seasonal, repeating at various intervals; Usually they are 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: mutation process, population waves, isolation and natural selection). The main significance comes down to random changes in the concentrations of various mutations contained in populations, as well as to the weakening of selection pressure when the number of individuals in the population increases and its intensification when the number of individuals decreases. The term sometimes refers to stages of development of flora and fauna, approximately corresponding to the change of geological cycles.
Evolutionary factors are factors causing the evolution of populations. “Waves of life” and “genetic drift”, as a rule, accompany the evolutionary process of each population, if we are talking about 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 causes that cause the death of organisms be considered natural selection? Natural selection is not the only reason for the death of organisms. The death of an animal may be the result of a random event (a forest fire, flood or other natural disaster that leaves no chance of survival).
Evolutionary factors Directing the evolutionary process Non-directing the evolutionary process Natural selection (against the background of the struggle for existence) - Hereditary variability. -- Genetic drift. - Waves of life. -- Isolation. 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 changes in the gene pools of these populations and the formation of new subspecies and species is called microevolution. Evolution at the level of systematic units above the species, which takes place over millions of years and is inaccessible to direct study, is called macroevolution. These two processes are one. Homework: Page Give examples of aromorphoses, idioadaptations and degenerations. Repeat the definitions: species, population, evolution, macroevolution, microevolution.