Describe the significance of hereditary variability in the life of organisms. Variability, its types and biological significance

Variability, its types and biological significance

Variability is a general property of living systems associated with variations in phenotype and genotype that arise under the influence of the external environment or as a result of changes in hereditary material. Distinguish between hereditary and non-hereditary variability.

Hereditary variability is combinative, mutational, indeterminate.

Combinational variability arises as a result of new combinations of genes during sexual reproduction, crossing over, and other processes accompanied by gene recombinations. As a result of combinative variability, organisms arise that differ from their parents in genotypes and phenotypes.

Mutational variability is associated with changes in the sequence of nucleotides in DNA molecules, loss and insertion of large sections in DNA molecules, changes in the number of DNA molecules (chromosomes). Themselves such changes are called mutations. Mutations are inherited.

Mutations are isolated:

Genes that cause changes in a particular gene. Gene mutations can be either dominant or recessive. Οʜᴎ can support or, conversely, inhibit the vital activity of the organism;

Generative, affecting reproductive cells and transmitted during sexual reproduction;

Somatic, not affecting the germ cells. They are not inherited in animals, but in plants they are inherited during vegetative reproduction;

Genomic (polyploidy and heteroploidy), associated with a change in the number of chromosomes in the karyotype of cells;

Chromosomal, associated with rearrangements of the structure of chromosomes, a change in the position of their sections, resulting from breaks, the loss of individual sections, etc. The most common gene mutations are those that result in a change, loss, or insertion of DNA nucleotides in a gene. Mutant genes transmit other information to the site of protein synthesis, and this, in turn, leads to the synthesis of other proteins and the emergence of new signs. Mutations can arise under the influence of radiation, ultraviolet radiation, and various chemical agents. Not all mutations are effective. Some of them are corrected during DNA repair. Phenotypically, mutations appear if they did not lead to the death of the organism. Most gene mutations are recessive. Phenotypically manifested mutations are of evolutionary importance, either providing individuals with advantages in the struggle for existence, or, conversely, entailing their death under the pressure of natural selection.

The mutational process increases the genetic diversity of populations, which creates the preconditions for the evolutionary process.

The frequency of mutations can be artificially increased, which is used for scientific and practical purposes.

Non-hereditary variability

Non-hereditary, or group (definite), or modification variability is a change in the phenotype under the influence of environmental conditions. Modification variability does not affect the genotype of individuals. The extent to which the phenotype can change is determined by the genotype. These limits are called the reaction rate. The reaction rate sets the boundaries within which a specific sign can change. Different signs have different reaction rates - wide or narrow. So, for example, the variability of the mammalian eye is small and has a narrow reaction rate. The milk yield of cows can vary over a fairly wide range, depending on the conditions of the breed.

The phenotypic manifestations of a trait are influenced by the cumulative interaction of genes and environmental conditions. The degree of manifestation of a trait is called expressiveness. The frequency of manifestation of a trait (%) in a population where all its individuals carry this gene is called penetrance. Genes can manifest themselves with varying degrees of expressiveness and penetration. For example, a baldness gene can manifest itself with a penetrance of 100% or 50%, depending on the specific environmental conditions, the number and interaction of genes responsible for the development of the trait.

Modification changes are not inherited in most cases, but they do not necessarily have a group character and do not always manifest themselves in all individuals of the species under the same environmental conditions. Modifications ensure the individual is adaptable to these conditions.

Remember how the genotype affects the manifestation of traits. What are mutations? How do mutations occur at the molecular genetic level?

In the process of individual development, some signs do not appear immediately and change throughout life. With the same genotype, different phenotypes can form. For example, if two organisms of the same genotype are kept in different conditions, then they will differ in phenotype. Plants grown from seeds of the same variety and even from one individual can differ in height, flowering time, and fruit size.

Variability is the ability of an organism to change in the process of individual development under the influence of various environmental conditions.

Types of variability. The phenotype is the result of the interaction of the genotype with different environmental conditions. Depending on the nature of the conditions affecting, changes may or may not be inherited. If the changes affect only the phenotype of the organism, then they are not inherited. In this case, the genotype is preserved, and the changes that have arisen in the process of individual development are not transmitted to the offspring. If changes affect the genotype of an organism, that is, its genes change, then such changes are inherited. Hence, two types of variability are distinguished - non-hereditary and hereditary.

Non-hereditary variability occurs in organisms under the direct influence of environmental conditions. For example, in a white hare in winter with low temperatures white wool grows, that is, no pigment is formed in the hair (Fig. 111). In the spring, when the temperature rises, pigment begins to be produced, and the coat becomes brown. Such variability of organisms is always adequate to environmental conditions and is adaptive. It contributes to the survival of individuals. So, the white fur of a white hare allows it to be invisible to its enemies against the background of white snow.

Rice. 111. Non-hereditary variability: 1 - change in the color of the coat of the white hare; 2 - dandelions grown on fertile (right) and poor (left) soil

Non-hereditary variability manifests itself gradually. These changes are manifested in many individuals in one group, that is, they are massive. So, all dandelions grown on fertile soil in the garden have a big increase and large inflorescences, and, conversely, on poor soil - low plants with small baskets (Fig. 111).

Hereditary variability. In contrast to non-hereditary variability, hereditary variability affects the genotype and is inherited. It can be combinative and mutational.

Combinative variability is associated with the emergence of new combinations of traits in organisms due to the combination of their genes. As a result, the offspring develop such traits that their parents might have lacked. For example, dachshunds are both long-haired and short-haired of different colors (Fig. 112). In humans, green, blue and brown eyes can be combined with light and dark hair in different combinations.

Rice. 112. Hereditary combinative variability of coat color and length in dachshunds

Combinative variability determines the diversity of individuals of the same species. It contributes to the appearance of such traits that are used by humans when breeding new varieties of plants and animal breeds.

Mutations are also referred to hereditary variability. You have already become acquainted with the peculiarity of this variability at the molecular-genetic level of the organization of life. The genotype of any organism is exposed to external factors that can cause "errors" in the structure of chromosomes or genes. As a result, a change in the genotype occurs and a new trait appears - a mutation. Different types of mutations are found in plants, animals, humans (Fig. 113).

Rice. 113. Hereditary mutational variability in different organisms: 1 - Drosophila with the wingless mutation (on the left - a normal winged individual); 2 - a grape variety with an increased set of chromosomes in cells (on the left - grapes with a normal set of chromosomes); 3 - the image of the polydactyly (polydactyl) mutation in Pope Sixtus II in Raphael's painting "The Sistine Madonna"

Mutations are associated not only with errors in DNA reduplication and protein synthesis, but also with abnormalities in chromosomes during cell division. Sometimes, when exposed to chemicals, the nucleus of a plant cell begins to divide faster than the cell itself. The result is cells with a doubled set of chromosomes. They develop plants that differ in a much larger size of flowers, fruits and leaves than specimens with a normal set of chromosomes (Fig. 113, 2). This has a positive meaning both for the plants themselves and for humans when they are grown in fields and gardens.

Mutational variability is of a spasmodic nature, there is no gradual change in the characteristics of organisms. Mutations are individual and occur in single individuals. Exposure to the same external conditions causes different mutations in each organism. For example, irradiation of wheat caryopses before sowing with X-rays leads in some cases to the formation of defective ears, in another case to the absence of an ear, in the third case to the formation of a larger ear. Thus, mutational variability is not predictable. According to their significance, mutations can be indifferent for organisms, that is, unnecessary, or useful, but most often they are harmful, since they reduce the viability of mutant organisms.

So, the development of a trait in any organism is the result of the interaction of its genotype with the external environment. The genotype and the environment, interacting, determine the development of the phenotype of the organism.

The biological significance of heredity and variability. Heredity and variability are two opposite properties of an organism that make up a single whole in nature. Heredity is realized in the process of reproduction, and variability - in the process of individual development of the organism. Heredity ensures the stability of the organism, its hereditary program and the transmission of certain traits in generations. Its implementation is based on DNA reduplication and the behavior of chromosomes in meiosis. The accuracy of these processes is a guarantee of the stability of the properties and functions of the body. Thus, heredity as a property of living things is realized at all levels of its organization. Heredity is conservative and is aimed at preserving the characteristics of the organism unchanged.

Variability is the phenomenon of instability of the hereditary properties of living things. It arises in the process of individual development of the organism. Non-hereditary variability is continuous. Changes arise as a result of the direct influence of the environment on the body. It is characterized by a series of gradual transitions from one form to another. The biological significance of non-hereditary variability is an increase in the adaptive capabilities of the organism and a variety of traits in individuals belonging to the same species.

The genotype is a fairly stable and conservative system, and the process of DNA replication is close to perfection. Gene persistence is of great biological importance. It ensures the consistency of the species and its invariability under relatively stable conditions. At the same time, the gene also has the ability to mutations and new combinations during sexual reproduction, which leads to a change in the genotype. In this case, hereditary changes are unpredictable. Hereditary variability is intermittent and individual. The differences between individuals are pronounced, and there are no intermediate forms.

Mutational variability is of particular importance. It occurs randomly when various factors affect the genotype. Mutations are not adequate to the influence of factors, they are single and diverse. V natural conditions each individual gene mutates very rarely. At first glance, it might seem that changes in genes are insignificant for an individual. But in reality, an organism has several thousand genes. Considering that mutations can occur in any of them, total number mutations rises sharply. Mutations are often harmful, as they change the adaptive characteristics of organisms. However, it is mutations that create a reserve of hereditary variability and play an important role in the process historical development organic world on Earth.

Exercises on the covered material

1. Give a definition of variability. What are the features of non-hereditary variability?
2. When does combinative variability occur?
3. How is mutational variability different from combinative variability?
4. Compare two properties of an organism: heredity and variability. Which one is primary and which is secondary?
5. In any organism, you can find signs typical of its parents. However, even in the offspring of the same parental pair, it is difficult to find two absolutely identical individuals if they are not twins. What is the reason for this?
6. Which of the two types of variability is more important for the historical development of the organic world on Earth? Justify the answer.

Variability is a process that reflects the relationship of the organism with the environment.

From a genetic point of view, variability is the result of the reaction of the genotype in the process of individual development of the organism to the conditions of the external environment.

Variability of organisms is one of the main factors of evolution. It serves as a source for artificial and natural selection.

Biologists distinguish between hereditary and non-hereditary variability. Hereditary variability includes such changes in the characteristics of an organism, which are determined by the genotype and persist in a number of generations. To non-hereditary variability, which Darwin called definite, and is now called modification, or phenotypic, variability, include changes in the characteristics of the organism; not preserved during sexual reproduction.

Hereditary variability represents a change in genotype, non-hereditary variability- change in the phenotype of the organism.

During the individual life of an organism, under the influence of environmental factors, it can experience two types of changes: in one case, the functioning changes, the action of genes in the process of forming traits, in the other, the genotype itself.

We got acquainted with hereditary variation resulting from combinations of genes and their interactions. The combination of genes is carried out on the basis of two processes: 1) independent distribution of chromosomes in meiosis and their random combination during fertilization; 2) crossing chromosomes and gene recombinations. Hereditary variability due to the combination and recombination of genes is usually called combinative variability... With this type of variability, the genes themselves do not change, their combination and the nature of interaction in the genotype system change. However, this type of hereditary variation should be considered as a secondary phenomenon, and a mutational change in the gene should be considered primary.

The source for natural selection is hereditary changes - both gene mutations and their recombinations.

Modification variability plays a limited role in organic evolution. So, if you take vegetative shoots from the same plant, for example, strawberries, and grow them in different conditions of humidity, temperature, illumination, on different soils, then despite the same genotype, they will be different. The action of various extreme factors can cause even greater differences in them. However, the seeds collected from such plants and sown under the same conditions will give the same type of offspring, if not in the first, then in subsequent generations. Changes in the characteristics of an organism caused by the action of environmental factors in ontogenesis disappear with the death of the organism.

At the same time, the ability for such changes, limited by the limits of the normal reaction of the genotype of the organism, has an important evolutionary significance. As shown by A.P. Vladimirsky in the 20s, V.S.Kirpichnikov and I.I.Shmalgauzen in the 30s, in the case when modification changes in the adaptive meaning arise when environmental factors constantly acting in a number of generations, which are capable of causing mutations that determine the same changes, the impression of a hereditary fixation of modifications can be created.

Mutational changes are necessarily associated with the reorganization of the reproductive structures of reproductive and somatic cells. The fundamental difference between mutations and modifications is that mutations can be accurately reproduced in a long series of cell generations, regardless of the conditions of the environment in which ontogenesis takes place. This is due to the fact that the occurrence of mutations is associated with a change in the unique structures of the cell - the chromosome.

On the issue of the role of variability in evolution, there was a long discussion in biology in connection with the problem of inheritance of the so-called acquired traits, put forward by J. Lamarck in 1809, partly adopted by Charles Darwin and still supported by a number of biologists. But the absolute majority of scientists considered the very formulation of this problem unscientific. At the same time, it must be said that the idea that hereditary changes in the body arise adequately to the action of the environmental factor is completely absurd. Mutations occur in many different directions; they cannot be adaptive for the organism itself, since they arise in single cells

And their action is realized only in the offspring. It is not the factor that caused the mutation, but only selection that evaluates the adaptive knowledge of the mutation. Since the direction and rate of evolution are determined by natural selection, and the latter is controlled by many factors of the internal and external environment, a false idea of ​​the initial adequate expediency of hereditary variability is created.

Selection based on single mutations "constructs" systems of genotypes that meet the requirements of those constantly operating conditions in which the species exists.

The term " mutation"Was first proposed by G. de Vries in his classic work" Mutation Theory "(1901-1903). He called a mutation the phenomenon of an abrupt, discontinuous change in a hereditary trait. The main provisions of de Vries' theory still have not lost their significance, and therefore they should be cited here:

1. the mutation occurs suddenly, without any transitions;
2. the new forms are completely constant, that is, they are stable;
3. mutations, in contrast to non-hereditary changes (fluctuations), do not form continuous rows, do not group around the middle type (mode). Mutations are qualitative changes;
4. mutations go to different directions, they can be both useful and harmful;
5. detection of mutations depends on the number of individuals analyzed to detect mutations;
6. the same mutations can occur repeatedly.

However, G. de Vries made a fundamental mistake in opposing the theory of mutations to the theory of natural selection. He incorrectly believed that mutations can immediately give rise to new species adapted to the external environment, without the participation of selection. In fact, mutations are only a source of hereditary changes that serve as material for selection. As we will see later, gene mutation is assessed by selection only in the genotype system. The mistake of G. de Vries is connected, in part, with the fact that the mutations he studied in evening primrose (Oenothera Lamarciana) later turned out to be the result of the splitting of a complex hybrid.

But one cannot but admire the scientific foresight made by G. de Vries regarding the formulation of the main provisions of the mutational theory and its significance for selection. Back in 1901, he wrote: “... mutation, mutation itself, should become an object of research. And if we ever manage to figure out the laws of mutation, then not only our view of the mutual kinship of living organisms will become much deeper, but we also dare to hope that the opportunity should open up just as well to master mutability as the breeder rules over variability, variability. Of course, we will come to this gradually, by mastering individual mutations, and this will also bring many benefits to agricultural and horticultural practices. Much that now seems unattainable will be in our power, if only we can learn the laws on which the mutation of species is based. Obviously, here we are waiting for an immense field of persistent work of high importance both for science and for practice. This is a promising area of ​​mutation dominance. " As we will see later, modern natural science is on the verge of understanding the mechanism of gene mutation.

The theory of mutations could develop only after the discovery of Mendel's laws and the patterns of gene linkage and their recombination as a result of crossing over, established in the experiments of the Morgan school. Only from the moment the hereditary discreteness of chromosomes was established, the theory of mutations received a basis for scientific research.

Although at present the question of the nature of the gene has not been completely clarified, nevertheless, a number of general laws of gene mutation have been firmly established.

Gene mutations occur in all classes and types of animals, higher and lower plants, multicellular and unicellular organisms, bacteria and viruses. Mutational variability as a process of qualitative leaps and bounds is universal for all organic forms.

Purely conditionally, the mutational process is divided into spontaneous and induced. In cases where mutations arise under the influence of ordinary natural environmental factors or as a result of physiological and biochemical changes in the body itself, they are referred to as spontaneous mutations... Mutations arising under the influence of special influences (ionizing radiation, chemicals, extreme conditions, etc.) are called induced. Fundamental differences there is no between spontaneous and induced mutations, but the study of the latter leads biologists to mastering hereditary variability and unraveling the mystery of the gene.

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Variability- This is a general property of living systems associated with changes in the phenotype and genotype that arise under the influence of the external environment or as a result of changes in hereditary material. Distinguish between non-hereditary and hereditary variability.

Non-hereditary variability... Non-hereditary, or group (specific), or modification variability- these are changes in the phenotype under the influence of environmental conditions. Modification variability does not affect the genotype of individuals. The genotype, while remaining unchanged, determines the limits within which the phenotype can change. These limits, i.e. opportunities for the phenotypic manifestation of a trait are called normal reaction and inherited... The reaction rate sets the boundaries within which a specific sign can change. Different signs have different reaction rates - wide or narrow. So, for example, such signs as blood type, eye color do not change. The shape of the mammalian eye changes slightly and has a narrow reaction rate. The milk yield of cows can vary over a fairly wide range, depending on the conditions of the breed. Other quantitative traits can also have a wide reaction rate - growth, leaf size, number of kernels on the cob, etc. The wider the reaction rate, the more opportunities an individual has to adapt to environmental conditions. That is why there are more individuals with an average severity of a trait than individuals with extreme expressions. This is well illustrated by such an example as the number of dwarfs and giants in humans. There are few of them, while there are thousands of times more people with a height in the range of 160-180 cm.

The phenotypic manifestations of a trait are influenced by the cumulative interaction of genes and environmental conditions. Modification changes are not inherited, but they do not necessarily have a group character and are not always manifested in all individuals of the species under the same environmental conditions. Modifications ensure the individual is adaptable to these conditions.

Hereditary variability(combinative, mutational, indefinite).

Combinative variability arises during the sexual process as a result of new combinations of genes arising during fertilization, crossing over, conjugation, i.e. during processes accompanied by recombinations (redistribution and new combinations) of genes. As a result of combinative variability, organisms arise that differ from their parents in genotypes and phenotypes. Some combinative changes can be detrimental to an individual. For a species, however, combinative changes are generally beneficial because lead to genotypic and phenotypic diversity. This contributes to the survival of species and their evolutionary progress.

Mutational variability associated with changes in the sequence of nucleotides in DNA molecules, loss and insertion of large sections in DNA molecules, changes in the number of DNA molecules (chromosomes). Themselves such changes are called mutations... Mutations are inherited.

Among the mutations are:

– gene- causing changes in the sequence of DNA nucleotides in a particular gene, and therefore in i-RNA and the protein encoded by this gene. Gene mutations can be either dominant or recessive. They can lead to the appearance of signs that support or depress the vital functions of the body;

– generative mutations affect germ cells and are transmitted during sexual reproduction;

– somatic mutations do not affect germ cells and are not inherited in animals, but in plants they are inherited during vegetative reproduction;

– genomic mutations (polyploidy and heteroploidy) are associated with a change in the number of chromosomes in the karyotype of cells;

– chromosomal mutations are associated with rearrangements of the structure of chromosomes, a change in the position of their sections resulting from breaks, the loss of individual sections, etc.

The most common gene mutations are those that result in a change, loss, or insertion of DNA nucleotides in a gene. Mutant genes transmit other information to the site of protein synthesis, and this, in turn, leads to the synthesis of other proteins and the emergence of new traits. Mutations can occur under the influence of radiation, ultraviolet radiation, and various chemical agents. Not all mutations are effective. Some of them are corrected during DNA repair. Phenotypically, mutations appear if they did not lead to the death of the organism. Most gene mutations are recessive. Phenotypically manifested mutations, which provided individuals with either advantages in the struggle for existence, or, on the contrary, caused their death under the pressure of natural selection, are of evolutionary importance.

The mutational process increases the genetic diversity of populations, which creates the preconditions for the evolutionary process.

The frequency of mutations can be artificially increased, which is used for scientific and practical purposes.

EXAMPLES OF TASKS

Part A

A1. Modification variability is understood as

1) phenotypic variability

2) genotypic variability

3) reaction rate

4) any changes to the trait

A2. Indicate the trait with the widest reaction rate

1) the shape of the swallow's wings

2) eagle beak shape

3) hare molt time

4) the amount of wool in a sheep

A3. Provide correct statement

1) environmental factors do not affect the genotype of an individual

2) it is not the phenotype that is inherited, but the ability to manifest it

3) modification changes are always inherited

4) modification changes are harmful

A4. Provide an example of a genomic mutation

1) the occurrence of sickle cell anemia

2) the emergence of triploid forms of potatoes

3) creating a tailless dog breed

4) the birth of an albino tiger

A5. Changes in the DNA nucleotide sequence in the gene are associated

1) gene mutations

2) chromosomal mutations

3) genomic mutations

4) combinative rearrangements

A6. A sharp increase in the percentage of heterozygotes in the cockroach population can lead to:

1) an increase in the number of gene mutations

2) the formation of diploid gametes in a number of individuals

3) chromosomal rearrangements in some members of the population

4) change in ambient temperature

A7. Accelerated skin aging in rural versus urban areas is an example

1) mutational variability

2) combination variability

3) gene mutations caused by ultraviolet radiation

4) modification variability

A8. The main cause of chromosomal mutation can be

1) replacement of a nucleotide in a gene

2) change in ambient temperature

3) violation of meiosis processes

4) insertion of a nucleotide into a gene

Part B

IN 1. What examples illustrate modification variability

1) a person's tan

2) a birthmark on the skin

3) the density of the coat of a rabbit of the same breed

4) increased milk yield in cows

5) six-fingered in humans

6) hemophilia

IN 2. Indicate events related to mutations

1) a multiple increase in the number of chromosomes

2) changing the undercoat of a hare in winter

3) replacement of an amino acid in a protein molecule

4) the appearance of an albino in the family

5) overgrowth of the root system of a cactus

6) the formation of cysts in protozoa

OT. Correlate the characteristic characterizing variability with its type

Part C

C1. What methods can be used to artificially increase the mutation frequency and why should this be done?

C2. Find errors in the text provided. Correct them. Indicate the numbers of sentences in which mistakes were made. Explain them.

1. Modification variability is accompanied by genotypic changes. 2. Examples of modification are lightening hair after prolonged exposure to the sun, increasing milk production of cows while improving feeding. 3. Information about modification changes is contained in genes. 4. All modification changes are inherited. 5. The manifestation of modification changes is influenced by environmental factors. 6. All signs of one organism are characterized by the same reaction rate, ie. limits of their variability.

The harmful effect of mutagens, alcohol, drugs, nicotine on the genetic apparatus of the cell. Protection of the environment from contamination by mutagens. Identification of sources of mutagens in environment(indirectly) and score possible consequences their effects on their own body. Hereditary human diseases, their causes, prevention

biochemical method, twin method, hemophilia, heteroploidy, color blindness, mutagens, mutagenesis, polyploidy.

Mutagens, mutagenesis

Mutagens- These are physical or chemical factors, the influence of which on the body can lead to a change in its hereditary characteristics. These factors include X-rays and gamma rays, radionuclides, heavy metal oxides, and certain types of chemical fertilizers. Some mutations can be caused by viruses. Genetic changes in generations can also lead to such widespread in modern society agents like alcohol, nicotine, drugs. The rate and frequency of mutations depend on the intensity of the influence of these factors. An increase in the frequency of mutations leads to an increase in the number of individuals with congenital genetic abnormalities. Mutations that affect the germ cells are inherited. However, mutations that occurred in somatic cells, can lead to cancer. Currently, studies are underway to identify mutagens in the environment and are being developed effective measures to neutralize them. Despite the fact that the frequency of mutations is relatively low, their accumulation in the gene pool of mankind can lead to a sharp increase in the concentration of mutant genes and their manifestation. That is why it is necessary to know about mutagenic factors and take on state level measures to combat them.

Medical genetics- chapter anthropogenetics studying hereditary human diseases, their origin, diagnosis, treatment and prevention. The main means of collecting information about a patient is medical genetic counseling. It is carried out in relation to persons who have had hereditary diseases among their relatives. The goal is to predict the likelihood of having children with pathologies, or to exclude the occurrence of pathologies.

Consulting stages:

- identification of the carrier of the pathogenic allele;

- calculation of the probability of having sick children;

- communication of the research results to future parents, relatives.

Hereditary diseases transmitted to offspring:

- gene linked to the X chromosome - hemophilia, color blindness;

- gene linked to the Y-chromosome - hypertrichosis (hair growth of the auricle);

- gene autosomal: phenylketonuria, diabetes mellitus, polydactyly, Huntington's chorea, etc.;

- chromosomal, associated with mutations of chromosomes, for example, cat cry syndrome;

- genomic - poly- and heteroploidy - change in the number of chromosomes in the karyotype of the organism.

Polyploidy- two- and more-fold increase in the number of haploid set of chromosomes in the cell. It arises as a result of nondisjunction of chromosomes in meiosis, duplication of chromosomes without subsequent cell division, fusion of nuclei of somatic cells.

Heteroploidy (aneuploidy)- a change in the number of chromosomes characteristic of a given species as a result of their uneven divergence in meiosis. It manifests itself in the appearance of an extra chromosome ( trisomy on chromosome 21 leads to Down's disease) or the absence of a homologous chromosome in the karyotype ( monosomy). For example, the absence of the second X chromosome in women causes Turner syndrome, which manifests itself in physiological and mental disorders. Sometimes polysomy occurs - the appearance of several extra chromosomes in the chromosome set.

Methods of human genetics. Genealogical - method of compiling pedigrees by various sources- stories, photographs, paintings. The traits of ancestors are clarified and the types of inheritance of traits are established.

Inheritance types: a) autosomal dominant, b) autosomal recessive, c) sex-linked inheritance.

The person for whom the pedigree is compiled is called proband .

Twin... A method for studying genetic patterns in twins. Twins can be identical (monozygotic, identical) and heterozygous (dizygotic, non-identical).

Cytogenetic... Method for microscopic examination of human chromosomes. Allows you to identify gene and chromosomal mutations.

Biochemical... Based on biochemical analysis, it can identify a heterozygous carrier of the disease, for example, a carrier of the phenylketonuria gene can be identified by an increased concentration phenylalanine in blood.

Population genetic... Allows you to compose the genetic characteristics of the population, to assess the degree of concentration of various alleles and the measure of their heterozygosity. For the analysis of large populations, the Hardy-Weinberg law is applied.

EXAMPLES OF TASKS

Part C

C1. Chorea of ​​Huntington - the hardest disease nervous system, is inherited as an autosomal trait (A).

Phenylketonuria - a disease that causes metabolic disorders, determined recessive gene, inherited by the same type. The father is heterozygous for the gene for Huntington's chorea and does not suffer from phenylketonuria. The mother does not suffer from Huntington's chorea and does not carry the genes that determine the development of phenylketonuria. What are the possible genotypes and phenotypes of children from this marriage?

C2. A woman with an absurd character married a man with a gentle character. From this marriage, two daughters and a son were born (Elena, Lyudmila, Nikolai). Elena and Nikolai turned out to be absurd in nature. Nikolay married a girl Nina with a gentle character. They had two sons, one of whom (Ivan) was a brawler, and the other a gentle man (Peter). Indicate on the pedigree of this family the genotypes of all its members.

Breeding, its tasks and practical significance. The teachings of N.I. Vavilov on the centers of diversity and origin of cultivated plants. The law of homologous series in hereditary variation. Methods for breeding new varieties of plants, animal breeds, strains of microorganisms. The value of genetics for breeding. Biological bases cultivation of cultivated plants and domestic animals

Basic terms and concepts tested in the examination paper: heterosis, hybridization, the law of homologous series of hereditary variability, artificial selection, polyploidy, breed, selection, cultivar, centers of origin of cultivated plants, pure line, inbreeding.

Genetics and breeding

Breeding - science, industry practical activities aimed at creating new varieties of plants, animal breeds, strains of microorganisms with stable hereditary traits, useful for humans. Theoretical basis breeding is genetics.

Breeding tasks:

- qualitative improvement of the trait;

- increasing productivity and productivity;

- increasing resistance to pests, diseases, climatic conditions.

Breeding methods. Artificial selection - preservation of organisms necessary for a person and elimination, culling of others that do not meet the goals of the breeder.

The breeder sets a task, selects parental pairs, selects offspring, conducts a series of closely related and distant crosses, then selects in each subsequent generation. Artificial selection happens individual and massive .

Hybridization- the process of obtaining new genetic combinations in offspring to enhance or a new combination of valuable parental traits.

Closely related hybridization (inbreeding) used to draw clean lines. The disadvantage is oppression of vitality.

Remote hybridization shifts the rate of reaction in the direction of strengthening the trait, the appearance of hybrid power (heterosis). The disadvantage is the non-breeding of the resulting hybrids.

Overcoming the sterility of interspecific hybrids. Polyploidy. G. D. Karpechenko in 1924 treated a sterile hybrid of cabbage and radish with colchicine. Colchicine caused nondisjunction of the hybrid chromosomes during gametogenesis. The fusion of diploid gametes led to the production of a polyploid hybrid of cabbage and radish (kapredki). The experiment of G. Karpechenko can be illustrated by the following scheme.

1. Before the action of colchicine

2. After the action of colchicine and artificial duplication of chromosomes:

Methods of work I.V. Michurina

IV Michurin, a domestic breeder, bred about 300 varieties of fruit trees, combining the qualities of southern fruits and the simplicity of northern plants.

Basic working methods:

- distant hybridization of geographically distant varieties;

- strict individual selection;

- "education" of hybrids by harsh growing conditions;

- "dominance control" with the help of the mentor method - grafting a hybrid to an adult plant that transfers its qualities to the bred variety.

Overcoming non-breeding during distant hybridization:

- method of preliminary approach - grafting of a cuttings of one species (mountain ash) was grafted onto the crown of a pear. Several years later, rowan flowers were pollinated with pear pollen. So a hybrid of rowan and pear was obtained;

- mediator method - 2 step hybridization. The almond was crossed with the semi-cultivated David peach, and then the resulting hybrid was crossed with the cultivar. Got Northern Peach;

- pollination with mixed pollen (own and foreign). An example is getting cerapadus - a hybrid of cherry and bird cherry.

Non-hereditary (phenotypic) variability- This is a type of variability, reflecting changes in the phenotype under the influence of environmental conditions that do not affect the genotype. The degree of its severity can be determined by the genotype. Phenotypic differences in genetically identical individuals arising from the influence of environmental factors are called modifications ... Distinguish between age, seasonal and ecological modifications. They boil down to a change in the severity of a trait. Violation of the structure of the genotype does not occur with them.

Age (ontogenetic) modifications are expressed in the form of a constant change of characters in the process of an individual's development. In humans, in the process of development, modifications of morphophysiological and mental characteristics are observed. For example, a child will not be able to develop correctly, both physically and intellectually, if in early childhood he will not be influenced by normal external and social factors... A child's long stay in a socially disadvantaged environment can cause an irreversible defect in his intellect.

Ontogenetic variability, like ontogeny itself, is determined by the genotype, where the individual's development program is encoded. However, the features of the formation of the phenotype in ontogenesis are due to the interaction of the genotype and the environment. Under the influence of unusual external factors, deviations in the formation of a normal phenotype may occur.

Seasonal modifications individuals or entire populations are manifested in the form of a genetically determined change in traits (for example, a change in the color of the coat, the appearance of puffs in animals), which occurs as a result of seasonal changes in climatic conditions. For example, for high temperatures the rabbit develops a white coat color, and at low - dark. In Siamese cats, depending on the season of the year, the fawn color of the coat changes to dark fawn and even brown.

Environmental modifications are adaptive changes in phenotype in response to changes in environmental conditions. Environmental modifications are phenotypically manifested in a change in the severity of a trait. They can arise in the early stages of development and persist throughout the life of an individual. Examples include large and small specimens of plants grown on soils containing different amounts nutrients; undersized and weakly viable individuals in animals that develop in poor conditions and do not receive enough nutrients necessary for life; the number of petals in the flowers of the liverwort, poplar, buttercup, the number of flowers in the inflorescence of plants, etc.

Environmental modifications affect quantitative (the number of petals in a flower, offspring in animals, weight of animals) and qualitative (skin color in humans under the influence of ultraviolet rays) signs.

Environmental modifications are reversible and with a change in generations, provided that the external environment changes, they may not appear. For example, the offspring of low-growing plants on well-fertilized soils will be of normal height; a person with crooked legs due to rickets has a completely normal offspring. If, in a number of generations, conditions do not change, the degree of expression of the trait in the offspring is preserved, then it is taken for a persistent hereditary trait (long-term modifications). When development conditions change, long-term modifications are not inherited. It was assumed that from well-trained animals, offspring are obtained with better "acting" data than from untrained ones. The offspring of trained animals is indeed easier to educate, but this is explained by the fact that it inherits not the skills acquired by the parental individuals, but the ability to train, due to the inherited type of nervous activity.

Most of the time modifications are worn adequate character, i.e. the severity of the trait is in direct proportion to the type and duration of action of one factor or another. Thus, improving livestock maintenance contributes to an increase in live weight of animals, fertility, milk yield and milk fat content. Modifications are worn adaptive, adaptive character. This means that in response to the changed environmental conditions, the individual exhibits such phenotypic changes that contribute to its survival. An example is the content of erythrocytes and hemoglobin in individuals who find themselves high above sea level. But, it is not the modifications themselves that are adaptive, but the ability of the organism to change depending on the environmental conditions.

One of the main properties of modifications is their mass character. It is due to the fact that the same factor causes approximately the same change in individuals that are genotypically similar.

Modification variability is caused by external factors, but its limit and the degree of expression of a trait are controlled by the genotype. For example, identical twins are phenotypically similar and even react in the same way to different conditions (for example, they most often suffer the same diseases). But the environment significantly affects the formation of signs. For example, in identical twins, freckles appear to varying degrees in different climates. In animals, a sharp deterioration in the diet can lead to weight loss in some and the death of others. In a person, with an equally enhanced diet, the hypersthenic will sharply increase in body weight, to a lesser extent - the normostenic, while the mass of the asthenic may not change at all. This indicates that the genotype controls not only the organism's ability to change, but also its limits. The modification limit is called normal reaction ... It is the reaction norm, and not the modifications themselves, that is inherited, i.e. the ability to develop a particular trait is inherited. The reaction rate is a specific quantitative self qualitative characteristic genotype, i.e. a certain combination of genes in the genotype and the nature of their interaction. Gene combinations and interactions include:

• polygenic determination of traits, when a part of the polygenes that control the development of a quantitative trait, depending on the conditions, can pass from the heterochromatin state to the euchromatin state and vice versa (the modification limit in this case is determined by the number of polygenes in the genotype);
• change in dominance in heterozygotes when external conditions change;
• different types of interaction of non-allelic genes;
• expressiveness of the mutation.

Distinguish signs with wide(weight, yield, etc.), narrow(for example, the percentage of fat in milk, the number of chicks in birds, the protein content in the blood in humans) and unambiguous reaction rate(most of the qualitative features: color of animals, color of hair and eyes in humans, etc.).

Sometimes individuals of a particular species are influenced by such harmful factors that it did not encounter in the process of evolution, and their toxicity is so great that it excludes the possibility of modification variability of the organism, determined by the reaction rate. Such agents can be lethal, or their action is limited to inducing developmental deformities. Deformities, or anomalies, of development are called morphoses. Morophoses - it various violations morphogenetic processes during the period of morphogenesis, leading to a sharp change in morphological, biochemical, physiological signs and properties of the organism. Examples of morphoses are defects in the development of wings and limbs in insects, deformities in shells in mollusks, and deformities in the physical structure of mammals. An example of morphoses in humans is the birth of children without limbs, with intestinal obstruction, a tumor of the upper lip, which took the character of an almost epidemic in 1961 in Germany and some countries Western Europe and America. The reason for the deformities was the fact that mothers in the first three months of pregnancy took as sedative thalidomide. A number of other substances (teratogens, or morphogens) are known that cause developmental deformities in humans. These include quinine, the hallucinogen LSD, drugs, alcohol. Morphoses are new, with no historical basis, the body's reactions to unusual harmful environmental factors. Phenotypically, they differ sharply from modifications: if modification- this is a change in the severity of the trait, then morphosis- this is a sharply changed, often qualitatively new sign.

Morphoses occur when harmful agents (morphogens) affect early processes embryonic development... Embryogenesis is subdivided into a number of stages during which the differentiation and growth of certain organs and tissues takes place. The development of a trait begins with a short period, called "critical". During this period, the body is distinguished by high sensitivity and a decrease in reparative (restorative) capabilities. In case of exposure to morphogens in critical periods the usual path of development of the primordium changes, since this induces an induced repression of the genes responsible for its formation. The development of this or that organ, as it were, jumps from one path to another. This leads to deviations from the normal development of the phenotype and to the formation of deformities. Disorders of embryogenesis are sometimes specific in nature, since their phenotypic expression depends on the stage of development of the organism at the time of exposure. A wide variety of toxic agents can cause the same or similar anomalies if the body is exposed to a strictly defined period of development, when the sensitivity of the corresponding tissues and organs is increased. Some morphogens ( chemical substances), due to their structural features, can cause specific morphoses as a result of selective exposure in a particular period of development.

Morphoses are not of an adaptive nature, since the body's response to the factors that indicate them is usually inadequate. The frequency of induced morphoses and the sensitivity of organisms to harmful agents-morphogens is controlled by the genotype and is different in different individuals of the same species.

Morphoses are often phenotypically similar to mutations and in such cases are called phenocopies. The mechanisms of occurrence of mutations and phenocopy are different: a mutation is a consequence of a change in the structure of a gene, and a phenocopy is the result of a violation of implementation hereditary information... Phenocopy can also occur due to the suppression of the function of certain genes. Unlike mutations, they are not inherited.

End of work -

This topic belongs to the section:

Introduction. Molecular basis of heredity

Introduction .. genetics from the Greek genesis origin as a science of regularities .. stage i years period of classical genetics the development of mendelism ..

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