Variability. Variability is the ability of organisms to acquire characteristics that their parent forms did not have.

Variability

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Variability is the ability of living organisms to acquire new characteristics and properties. Thanks to variability, organisms can adapt to changing environmental conditions.

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There are two types of variability: Non-hereditary, or phenotypic, - variability in which no changes in the genotype occur. It is also called group, specific, modification. Hereditary, or genotypic, individual, uncertain - changes in the characteristics of an organism caused by a change in the genotype; it can be: combinative - arising as a result of recombination of chromosomes in the process of sexual reproduction and sections of chromosomes in the process of crossing over; mutational - arising as a result of a sudden change in the state of genes;

Slide 5: Modification variability - variability of organisms that occurs under the influence of environmental factors and does not affect the genotype

Patterns of variability Modification variability - variability organisms arising under the influence of factors external environment and does not affect the genotype. A change that is not hereditary is not significant for us. Charles Darwin

Slide 6: Signs of the body

qualitative (they can be described): coloring (color); form; blood type; milk fat content, etc. quantitative (they can be measured): length (height); weight; volume; number of seeds, etc.

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Which characteristics (qualitative or quantitative) are more susceptible to variability? Will these changes be evident in future generations? Why? Is the degree of variation of a trait the same in all individuals of a given species? Why?

Slide 8: Qualitative and quantitative characteristics: qualitative - established descriptively: - color of animals, color of seeds, growth. Less susceptible to environmental influences. Quantitatively determined by measurement: - yield of agricultural crops, milk yield of cows, egg production of chickens. More susceptible to environmental influences

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The limits of modification variability of a trait are called its reaction norm. The reaction norm is an inherited trait.

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Slide 10: A strange object is growing on the river, The water will twist the lower leaves, The middle one will lay on the water like a raft, The upper one will slide towards the sky like an arrow

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Patterns of variability The same genotype can give different values ​​of a trait under different conditions. Some signs have a broad reaction norm, others have a much narrower one. Arrowhead has two types of leaves: - underwater above-water The main factor responsible for the development of leaf shape is the degree of illumination. ! Give examples of traits with a narrow and broad reaction norm.

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Modification variability As a rule, quantitative traits (plant height, yield, leaf size, milk yield of cows, egg production of chickens) have a wider reaction rate, that is, they can vary widely than qualitative traits (coat color, milk fat content, flower structure, group blood). Knowledge of reaction norms has great importance for practice Agriculture Thus, modification variability is characterized by the following basic properties: 1. Non-heritability; 2. Group nature of changes; 3. Correspondence of changes to the influence of environmental factors.

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Statistical patterns of modification variability. Modification variability of many characteristics of plants, animals and humans obeys general laws. These patterns are identified based on the analysis of the manifestation of the trait in a group of individuals (n). The degree of expression of the studied trait among members of the sample population is different. Each specific value of the characteristic being studied is called a variant and is designated by the letter v. When studying the variability of a trait in a sample population, a variation series is compiled in which individuals are arranged in ascending order of the indicator of the trait being studied.

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Based on the variation series, a variation curve is constructed - a graphical display of the frequency of occurrence of each variant. The frequency of occurrence of individual variants is denoted by the letter p. For example, if you take 100 ears of wheat (n) and count the number of ears in an ear, then this number will be from 14 to 20 - this is the numerical value of option (v). Variation series: v = 14 15 16 17 18 19 20 Frequency of occurrence of each variant p = 2 7 22 32 24 8 5 The average value of the characteristic is more common, and variations significantly different from it are much less common. This is called a normal distribution. The curve on the graph is usually symmetrical. Variations, both larger than average and smaller, occur equally frequently.

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It is easy to calculate the average value of this characteristic. To do this, use the formula:  (v ּ p) M = n where M is the average value of the characteristic, in the numerator is the sum of the products of the variant by their frequency of occurrence, in the denominator is the number of variants. For this characteristic, the average value is 17.13. Knowledge of the patterns of modification variability is of great importance practical significance, since it allows one to anticipate and plan in advance the degree of expression of many characteristics of organisms depending on environmental conditions.

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Slide 16: Patterns of variability

Hereditary Non-hereditary Change in genotype Change in phenotype Inherited Not inherited Individual Mass Independent, harmful or beneficial Adaptive Not adequate to the environment Adequate to the environment Leads to the formation of combinations and mutations Leads to the formation of modifications Causes – ionizing radiation, toxic substances, etc. Causes – climatic, food, etc. changes

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Slide 17: Combinative hereditary variability

Possibility of occurrence of combinations: Prophase I of meiosis – crossing over; Anaphase I – independent divergence of homologous chromosomes; Anaphase II - independent chromatid separation Random fusion of gametes

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Slide 18: CONCLUSIONS:

Patterns of variability CONCLUSIONS: Variability manifests itself in all organisms and is their property. There are hereditary and non-hereditary (modification) variability. The limits of modification variability of a trait are called reaction norms. Modifications (modification changes) do not affect the genotype; are not inherited; arise under the influence of environmental factors; manifest themselves in a similar way in many individuals of the species; may disappear over time. Possible only within the normal range of reactions, i.e. determined by genotype. It is not the trait itself that is inherited, but the ability to express this trait under certain conditions, i.e. the norm of the body's reaction to external conditions is inherited.

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Forms of variability

• Hereditary, or genotypic, variability is changes in the characteristics of an organism caused by changes in the genotype. It, in turn, is divided into combinative and mutational. Combinative variability arises due to the recombination of hereditary material (genes and chromosomes) during gametogenesis and sexual reproduction. Mutational variability arises as a result of changes in the structure of hereditary material.
• Non-hereditary, or phenotypic, or modification, variability is changes in the characteristics of an organism that are not caused by a change in the genotype.

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Mutation theory

1. Mutations arise suddenly, spasmodically, without any transitions.
2. Mutations are hereditary, i.e. are persistently passed on from generation to generation.
3. Mutations do not form continuous series, are not grouped around an average type (as with modification variability), they are qualitative changes.
4. Mutations are non-directional - any locus can mutate, causing changes in both minor and vital signs in any direction.
5. The same mutations can occur repeatedly.
6. Mutations are individual, that is, they occur in individual individuals.

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• The process of mutation occurrence is called mutagenesis, and environmental factors causing mutations are called mutagens.

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According to the type of cells in which the mutations occurred, they distinguish

• Generative mutations occur in germ cells, do not affect the characteristics of a given organism, and appear only in the next generation.
• Somatic mutations arise in somatic cells, are manifested in a given organism and are not transmitted to offspring during sexual reproduction. Somatic mutations can be preserved only through asexual reproduction (primarily vegetative).

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According to the adaptive value of mutations there are

• Useful - increase vitality.
• Lethal - cause death.
• Semi-lethal - reduce vitality.
• Neutral - do not affect the viability of individuals.

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According to the nature of their manifestation, mutations can be

• Dominant (appearing more often).
• Recessive (appearing less frequently).
• If a dominant mutation is harmful, then it can cause the death of its owner in the early stages of ontogenesis.
• Recessive mutations do not appear in heterozygotes, therefore long time are preserved in the population in a “hidden” state and form a reserve of hereditary variability.
• When environmental conditions change, carriers of such mutations may gain an advantage in the struggle for existence.

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According to the level of hereditary material in which the mutation occurred, they are distinguished

• Gene mutations
• Chromosomal mutations
• Genomic mutations

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Gene mutations

• These are changes in gene structure.
• Since a gene is a section of a DNA molecule, a gene mutation represents changes in the nucleotide composition of this section.
• Gene mutations can occur as a result of:

1) replacing one or more nucleotides with others;

2) nucleotide insertions;

3) loss of nucleotides;

4) doubling of nucleotides;

5) changes in the order of alternation of nucleotides.

• These mutations lead to changes in the amino acid composition of the polypeptide chain and, consequently, to changes in the functional activity of the protein molecule. Gene mutations result in multiple alleles of the same gene.
• Diseases caused by gene mutations are called genetic diseases (phenylketonuria, sickle cell anemia, hemophilia, etc.). The inheritance of gene diseases obeys Mendel's laws.

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Chromosomal mutations

• These are changes in the structure of chromosomes. Rearrangements can occur both within one chromosome - intrachromosomal mutations (deletion, inversion, duplication, insertion), and between chromosomes - interchromosomal mutations (translocation).

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Intrachromosomal mutations

• Deletion - loss of a section of a chromosome
• Inversion - rotation of a chromosome section by 180°
• Duplication - doubling of the same part of a chromosome
• Insertion - rearrangement of a section

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Intrachromosomal mutations

1 - pair of chromosomes; 2 - deletion; 3 - duplication; 4, 5 - inversion; 6 - insertion.

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Interchromosomal mutations

• Translocation is the transfer of a section of one chromosome or an entire chromosome to another chromosome.
• Diseases caused by chromosomal mutations are classified as chromosomal diseases.
• Such diseases include “cry of the cat” syndrome (46, 5p-), translocation variant of Down syndrome (46, 21 t2121), etc.

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Genomic mutations

• A genomic mutation is a change in the number of chromosomes. Genomic mutations occur as a result of disruption of the normal course of mitosis or meiosis.
• Haploidy is a decrease in the number of complete haploid sets of chromosomes.
• Polyploidy is an increase in the number of complete haploid sets of chromosomes: triploids (3n), tetraploids (4n), etc.
• Heteroploidy (aneuploidy) is a multiple increase or decrease in the number of chromosomes. Most often, there is a decrease or increase in the number of chromosomes by one (less often two or more).

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Heteroploidy

• The most likely cause of heteroploidy is the nondisjunction of any pair of homologous chromosomes during meiosis in one of the parents.
• In this case, one of the resulting gametes contains one less chromosome, and the other contains one more.
• The fusion of such gametes with a normal haploid gamete during fertilization leads to the formation of a zygote with a smaller or larger number of chromosomes compared to the diploid set characteristic of a given species: nullosomy (2n - 2), monosomy (2n - 1), trisomy (2n + 1) , tetrasomy (2n + 2), etc.

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Artificial mutations

• Spontaneous mutagenesis constantly occurs in nature, but spontaneous mutations are a fairly rare occurrence, for example, in Drosophila, the white eye mutation is formed with a frequency of 1:100,000 gametes.
• Factors whose impact on the body leads to mutations are called mutagens. Mutagens are usually divided into three groups.
• Physical and chemical mutagens are used to artificially produce mutations.

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• Induced mutagenesis is of great importance because it makes it possible to create valuable starting material for breeding, and also reveals ways to create means of protecting humans from the action of mutagenic factors.

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“Patterns of variability: modification and mutational variability” 01/28/2013 Lesson topic: Lesson goal: -to form the concept of modification and mutational variability; -consider the mechanism of mutations; - find out the causes of mutations; -study the main characteristics of mutational variability.

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Variability is the ability of living organisms to acquire new characteristics in the process of ontogenesis. Heredity is the property of all living organisms to transmit their characteristics and properties from generation to generation.

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An example of modifying variability in a person is tanning, which gradually disappears in winter. Modifying variability is not associated with changes in genes, chromosomes or the genotype as a whole and occurs under the influence of environmental factors.

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Pines of the same population differ from each other, as they develop in different conditions. The relationship between phenotype and genotype

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Reaction norm The limits of modification variability of any trait are called the reaction norm. It is not the trait itself that is inherited, but the ability to manifest this trait under certain conditions, or we can say that the norm of the body’s reaction to external conditions is inherited. Maple leaves have different sizes, since heat and light are not distributed evenly.

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Main characteristics of modification variability: Modification changes are not transmitted from generation to generation. Modification changes occur in many individuals of the species and depend on the effect of environmental conditions on them. Modification changes are possible only within the limits of the reaction norm; ultimately, they are determined by the genotype.

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Genotypic variability is associated with changes in the genotype and is the result of mutations.

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The term “mutation” was first proposed in 1901. Dutch scientist Hugo de Vries.

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Mutations are changes in the genotype that occur under the influence of external and internal environment. The process of mutations is called mutagenesis, and the factor causing mutation is called a mutagen. Mutations Gene mutations are associated with changes in the nucleotide sequence of a DNA molecule. Chromosomal mutations are associated with changes in chromosome structure. Genomic mutations lead to changes in the number of chromosomes.

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Gene, or point, mutations are changes in the sequence of nucleotides in a DNA molecule. Gene mutations should be considered as the result of “errors” that occur during the duplication of DNA molecules. A gene mutation occurs on average in one in 100,000 gametes. But since the number of genes in the human body is large, almost every individual carries a newly emerged mutation.

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Albinism Albinism is a congenital absence of pigment in the skin, hair, iris and pigment membranes of the eye. External manifestations In some forms of albinism, there is a decrease in the color intensity of the skin, hair and iris, while in others the color of the latter mainly changes. Changes in the retina may occur, and various vision disorders may occur, including nearsightedness, farsightedness and astigmatism, as well as increased sensitivity to light and other abnormalities. Albino people have white skin (which is especially noticeable in non-Caucasian groups); their hair is white (or they are blond). The frequency of albinos among the peoples of European countries is estimated at approximately 1 per 20,000 inhabitants. In some other nationalities, albinos are more common. Thus, in a study of 14,292 black children in Nigeria, 5 albinos were found among them, which corresponds to a frequency of about 1 in 3,000, and among the Indians of Panama (San Blas Bay) the frequency was 1 in 132.

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Color blindness Daltoni zm, color blindness is a hereditary, less commonly acquired feature of vision, expressed in the inability to distinguish one or more colors. Named after John Dalton, who first described a type of color blindness based on his own sensations in 1794.

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Hemophilia Hemophilia is a hereditary disease associated with impaired coagulation (blood clotting process); with this disease, hemorrhages occur in the joints, muscles and internal organs, both spontaneous and as a result of injury or surgery. With hemophilia, the risk of death of the patient from hemorrhage in the brain and other vital organs, even with minor trauma, increases sharply. Patients with severe hemophilia are subject to disability due to frequent hemorrhages in the joints (hemarthrosis) and muscle tissue (hematomas). Usually, men suffer from hemophilia, and women are carriers of the diseased gene.

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Chromosomal mutations are rearrangements of chromosomes. A deletion is the loss of a section of a chromosome. Duplication is the doubling of a section of a chromosome. Inversion is a rotation of a chromosome section by 180°. Translocation is the exchange of sections of non-homologous chromosomes. Fusion of two non-homologous chromosomes into one.

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A disease caused by an anomaly of chromosome set (change in the number or structure of autosomes), the main manifestations of which are mental retardation, a peculiar appearance patient and congenital malformations. One of the most common chromosomal diseases, occurs with an average frequency of 1 in 700 newborns. Down's disease

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Down syndrome The disease occurs equally often in boys and girls. Children with Down syndrome are more often born to elderly parents. If the mother's age is 35 - 46 years, then the probability of having a sick child increases to 4.1%; with the age of the mother, the risk increases. The possibility of a second case of the disease in a family with trisomy 21 is 1 - 2%.

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Klinefelter's syndrome Klinefelter's syndrome occurs in 1 in 500 boys. The extra X chromosome is inherited from the mother in 60% of cases, especially during late pregnancy. The risk of inheriting a paternal chromosome does not depend on the age of the father. Klinefelter syndrome is characterized by the following symptoms: tall stature, disproportionately long legs. Disturbances in the development of the genital organs are detected during puberty and later. Patients are usually infertile.

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45 chronicles - XO The height of adult patients is 20-30 cm below average. Treatment of patients with this syndrome is complex and includes reconstructive and plastic surgery, hormonal therapy (estrogens, growth hormone), and psychotherapy.

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Shereshevsky-Turner syndrome Shereshevsky-Turner syndrome is the only form of monosomy in live births. Clinically, Shereshevsky-Turner syndrome is manifested by the following symptoms. Underdevelopment of the genital organs or their absence. There are various defects of the cardiovascular system and kidneys. There is no decrease in intelligence, but patients exhibit emotional instability. Appearance patients is peculiar. Characteristic symptoms are noted: a short neck with excess skin and wing-like folds; in adolescence, retardation in growth and development of secondary sexual characteristics is detected; Adults are characterized by skeletal disorders, low position of the ears, body disproportions (shortened legs, relatively wide shoulder girdle, narrow pelvis). summary of presentations

Variability

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Topic: “Hereditary variability.” Objectives: To characterize hereditary variability ( Additional Information in the buffer, below). Variability. Genetics studies not only heredity, but also the variability of organisms. Variability is the ability of living organisms to acquire new characteristics and properties. Thanks to variability, organisms can adapt to changing environmental conditions. There are two types of variability: Non-hereditary, or phenotypic, - variability in which no changes in the genotype occur. Mutational variability. 1848-1935 Dutch botanist, geneticist. - Variability.ppt

"Variation" biology

Variability. What does genetics study? "Variation" biology. "Variation" biology. Property of living organisms. Forms of variability of organisms. Forms of variability. Patterns of modification variability. Read the concepts, give them a formulation. Environmental factors. Variability of the body that occurs under the influence of factors. Identification of patterns of modification variability. Make a table. Using the data from the variation series, construct a variation curve. Variation curves of variability of morphofunctional parameters. "Variation" biology. Norm of reaction. - “Variability” biology.ppt

Variability of characters

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Variability. The ability of organisms to acquire characteristics. Variation resulting from crossing. Modification variability. Two cuttings. Phenotype. 6. Plant. Reason for change. Non-heritability. Group nature of changes. The meaning of the changes. Types of phenotypic variability. Determination of the limits of variability by genotype. The reaction rate for a certain plant species. 15. Construction of a variation curve. Variation series. Genotypic variability. Combinative. Combinative variability. Neck length and leg length. Sources of genetic variation. Mutations. - Variability of features.pptx

Variability of living organisms

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General biology. What does genetics study? Variability of living organisms. Variability of living organisms. Variability. Forms of variability of organisms. Forms of variability. Patterns of modification variability. Concepts. Gene. Variability of the body. Laboratory work. Variation series of variability. Variation series data. Variation curves. Variability of living organisms. Norm of reaction. Average values ​​of the characteristic. Characteristics of modification variability. Average value of the attribute. Variability of living organisms. Hereditary (genotypic) variability. Combinative variability. - Variability of living organisms.ppt

Variability of characteristics of organisms

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Variability of signs in an organism. The ability of an organism to change during ontogenesis. Variability. Non-hereditary variability. Combinative variability. Variability of characteristics of organisms. Mutational variability. Mutation. Gene mutations. Genomic mutations. Biological significance of heredity. - Variability of characteristics of organisms.ppt

Variability in humans

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Genetic phenomenon. Types of variability. Chromosomal abnormalities. Variability. Information sources. Property of all living organisms. According to the mechanisms of occurrence, variability is divided into: Variability in humans. Modification variability. Classification of modification variability. Modifications are not inherited. Monozygotic twins. Twins. Trait in pairs of monozygotic and dizygotic twins. Twin method. Combinative variability. Marriage systems. Human. Mutational variability. Changes in hereditary material. Classification of mutagens. Teratogens. Congenital defects. - Variability in humans.ppt

Patterns of variability

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General biology. Variability. What does genetics study? What is heredity? How are hereditary traits transmitted? Forms of variability. Hereditary mutation genotypic. Non-hereditary phenotypic modification. Lesson topic: Patterns of modification variability. Gene Phenotype Environmental factors Trait Genotype. Gene. Protein. Sign. Genotype. Phenotype. Environmental factors. “The program of action of genes in the genotype system resembles the score of a symphony. Physical education minute. Laboratory work. Topic: Identification of patterns of modification variability. - Patterns of variability.ppt

Heredity and variability

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On the topic: History of the development of genetics. GENETICS (from the Greek genesis - origin), a science that studies the patterns of heredity and variability of organisms. Various speculative ideas about heredity and variability were expressed by ancient philosophers and doctors. The most valuable data were obtained by I. Kelreuter and A. Gertner (Germany), O. Sajray and C. Naudin (France), T. Knight (England). Darwin himself put a lot of effort into studying heredity and variation. The most detailed was the third hypothesis, proposed by the German zoologist A. Weissmann. - Heredity and variability.ppt

Heredity and variability of organisms

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General lesson. Knowledge about the organismic level of life. Use knowledge and skills. Triangle of knowledge. Multi-level credit. Difficulty level. Basic biological concepts. Basic genetic terms. Genetics. Level. Basic patterns of heredity and variability. Founder of genetics. Dominance rule. The splitting rule. Law of independent inheritance of characteristics. Laws of inheritance. Laws of heredity. Variability. Jean Baptiste Lamarck. Heredity and variability of organisms. Modification variability. Patterns of variability. - Heredity and variability of organisms.pptx

Non-hereditary variability

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Integrated lesson on the topic “Non-hereditary variability” (biology and computer science). Purpose of the lesson: Lesson plan: Non-hereditary variability. Phenotype = genotype + environment. Reason for change. Changing environmental conditions. White cabbage does not form a head of cabbage in hot climates. The meaning of the changes. Adaptation – adaptation to given environmental conditions, survival, preservation of offspring. Breeds of horses and cows brought to the mountains become stunted. Properties of modification variability. Non-heritability. Group nature of changes. Determination of the limits of variability by genotype. - Non-hereditary variability.ppt

Types of variability

Patterns of variability. Identify types of variability. Variability. Modification variability. Variation in leaf shape. Genotype of Drosophila larva. Modifications. Limits of modification variability. Instruction card. An object. Hereditary variability. Hereditary variability. Hereditary variability. Hereditary variability. Types of mutations. Changes in chromosome structure. Polyploidy. Down syndrome. Klinefelter's syndrome. Shereshevsky-Turner syndrome. Factors causing mutations. - Types of variability.ppt

Forms of variability

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Variability. Modification variability. Norm of reaction. The evolutionary significance of the reaction norm. Phenotype. Calculation of the average value of a characteristic. Hereditary variability. Mutations and their causes. Colchicum. Forms of variability. Forms of variability. Classification of mutations. Classification of mutations. Forms of variability. Mutations. Base pair substitutions. Phenylktouria. Gene mutation. Deletion. Inversion. Marfan syndrome. Spinal atrophy. Monosomic. Lejean's syndrome. Down syndrome. Genomic mutations of monoploid organisms. Violations related to various types aneuploidy in humans. Chromosomes. - Forms of variability.ppt

Types of variability

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Patterns of variability. Objective of the lesson: identify types of variability. Variability is the ability of organisms to acquire new characteristics. Modification variability. Variability of leaf shape in arrowhead rooting underwater. Modification variability. Modifications are not inherited. Limits of modification variability. Instruction card for laboratory work. Draw a conclusion. Hereditary variability. Hereditary variability. Hereditary variability. Hereditary variability. Types of mutations. Chromosomal – changes in the structure of chromosomes. Polyploidy is a multiple increase in the number of chromosomes in a cell. - Types of variability.ppt

Meaning and types of variability

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Variation, its causes and significance for evolution and selection. Types of variability. Hereditary variability. Non-hereditary variability. Law of homological series. Types and genera. Plant families. Modification variability. Norm of reaction. Norm of reaction of a quantitative trait. K. Naegeli. Rigorous quantitative approach. Bean variety. Reason for modification variability. Homogeneous genetic material. Adaptive modification mechanism. Ontogenetic variability. Functional changes. Morphoses. The degree of severity of morphosis. Phenotypic manifestation of mutations. -

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Topic: “Modification variability” Pimenov A.V. Objectives: To characterize non-hereditary variability

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Variability Genetics studies not only heredity, but also the variability of organisms. Variability is the ability of living organisms to acquire new characteristics and properties. Thanks to variability, organisms can adapt to changing environmental conditions. There are two types of variability: Non-hereditary, or phenotypic, - variability in which no changes in the genotype occur. It is also called group, specific, modification. Hereditary, or genotypic, individual, uncertain - changes in the characteristics of an organism caused by a change in the genotype; it can be: combinative - arising as a result of recombination of chromosomes in the process of sexual reproduction and sections of chromosomes in the process of crossing over; mutational - arising as a result of a sudden change in the state of genes;

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White hare in summer and winter. Variability? Modification, the genotype does not change. Ermine rabbit at elevated temperature remains white. Variability? Modification, the genotype does not change.

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Modification variability An important role in the formation of the characteristics of an organism is played by its habitat. Each organism develops and lives in a certain environment, experiencing the action of its factors that can change the morphological and physiological properties of organisms, i.e. their phenotype. A classic example of the variability of characteristics under the influence of environmental factors is the variety of leaves in the arrowhead: leaves immersed in water have a ribbon-like shape, leaves floating on the surface of the water are round, and those in the air are arrow-shaped. If the entire plant is completely immersed in water, its leaves are only ribbon-shaped.

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Modifying variability Under the influence of ultraviolet rays, people (if they are not albinos) develop a tan as a result of the accumulation of melanin in the skin, and the intensity of skin color varies among different people. Thus, changes in a number of characteristics of organisms are caused by the action of environmental factors. Moreover, these changes are not inherited. So, if you get offspring from newts raised on dark soil and place them on light soil, then they will all have a light color, and not dark like their parents. That is, this type variability does not affect the genotype and therefore is not transmitted to descendants.

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Modification variability Variability in organisms that occurs under the influence of environmental factors and does not affect the genotype is called modification. Modification variability is of a group nature, that is, all individuals of the same species placed in the same conditions acquire similar characteristics. For example, if a vessel with green euglena is placed in the dark, then they will all lose their green color, but if they are again exposed to light, they will all become green again. Modification variability is definite, that is, it always corresponds to the factors that cause it. Thus, ultraviolet rays change the color of human skin, and increased physical activity affects the degree of muscle development.

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Modification variability Non-adaptive modifications: morphoses and phenocopies. Morphoses are non-hereditary changes caused by extreme or unusual environmental factors (X-ray morphoses, chemomorphoses) that change somatic cells. Morphoses are considered as “deformities” that are not inherited and are not adaptive in nature. For example, when Drosophila larvae are irradiated, they obtain imagoes with notches in various parts of the wing, which are a consequence of the death of part of the cells of the imaginal discs of the wing due to irradiation. Phenocopies are non-hereditary changes similar to known mutations. Phenocopies are the result of the action of physical and chemical agents on a genetically normal organism. For example, when using thalidomide, children were often born with fecomelia - shortened flipper-like arms, which can also be caused by mutant alleles.

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Modification variability Despite the fact that signs can change under the influence of environmental conditions, this variability is not unlimited. Thus, in a wheat field you can find plants with large ears (20 cm or more) and very small ones (3-4 cm). This is explained by the fact that the genotype determines certain boundaries within which a change in a trait can occur. The degree of variation of a trait, or the limits of modification variability, is called the reaction norm.

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Modification variability As a rule, quantitative traits (plant height, yield, leaf size, milk yield of cows, egg production of chickens) have a wider reaction rate, that is, they can vary widely than qualitative traits (coat color, milk fat content, flower structure, group blood). Knowledge of the reaction norm is of great importance for agricultural practice. Thus, modification variability is characterized by the following basic properties: 1. Non-heritability; 2. Group nature of changes; 3. Correspondence of changes to the influence of environmental factors.

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Modification variability To assess the degree of expression of the studied trait, the concept is used: EXPRESSION - the degree of phenotypic manifestation of the gene. This indicator depends on the interaction of the gene with other genes, or on the effect external conditions. The presence of a given gene does not always mean that it will manifest itself in the phenotype. To estimate the number of individuals in which this trait is phenotypically manifested, the term PENETRANCE is used. Penetrance is the frequency of phenotypic manifestation of a trait in individuals with the same genotype for this gene. The penetrance of congenital hip dislocation is, for example, 20%, in diabetes mellitus it is 65%.

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Modification variability Statistical patterns of modification variability. Modification variability of many characteristics of plants, animals and humans obeys general laws. These patterns are identified based on the analysis of the manifestation of the trait in a group of individuals (n). The degree of expression of the studied trait among members of the sample population is different. Each specific value of the characteristic being studied is called a variant and is designated by the letter v. When studying the variability of a trait in a sample population, a variation series is compiled in which individuals are arranged in ascending order of the indicator of the trait being studied.

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Modification variability Based on the variation series, a variation curve is constructed - a graphical display of the frequency of occurrence of each variant. The frequency of occurrence of individual variants is denoted by the letter p. For example, if you take 100 ears of wheat (n) and count the number of ears in an ear, then this number will be from 14 to 20 - this is the numerical value of option (v). Variation series: v = 14 15 16 17 18 19 20 Frequency of occurrence of each variant p = 2 7 22 32 24 8 5 The average value of the characteristic is more common, and variations significantly different from it are much less common. This is called a normal distribution. The curve on the graph is usually symmetrical. Variations, both larger than average and smaller, occur equally frequently.

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Modification variability It is easy to calculate the average value of this characteristic. To do this, use the formula: (v p) M = n where M is the average value of the characteristic, the numerator is the sum of the products of the option by their frequency of occurrence, the denominator is the number of options. For this characteristic, the average value is 17.13. Knowledge of the patterns of modification variability is of great practical importance, since it allows one to anticipate and plan in advance the degree of expression of many characteristics of organisms depending on environmental conditions.