Interaction of genes. Lesson plan and presentation in biology on the topic "Interaction of genes and their multiple actions" (Grade 9)

A gene is a structural unit of inherited information. It is a specific area (sometimes RNA). The interaction of genes ensures the transfer of elementary traits of parental organisms to offspring.

Each gene determines a specific trait that does not depend on others. They are able to interact. This is possible due to what happens genes. When combined into a genotype, they act as a system. The main relationships between them are dominance and recessiveness.

The human genotype is thousands of traits (system) that fit in just 46 chromosomes. Each of them contains a huge number of genes (at least 30 thousand).

The degree of development of a particular trait may be due to the influence of not one gene, but a number of which are interconnected in a free way. This interaction of genes is commonly called polymerism (polycomplexity). According to this mechanism, skin color, hair color and hundreds of other traits are inherited.

Thanks to such a number of genes, the vital activity and development of definitive organisms, consisting of various types of specialized differentiated cells, is ensured. About 200 cell types have been identified in humans, with additional subdivisions into a number of more specialized functionally and morphologically cell types.

The connection of genes in one chromosome is defined by the term linkage of genes. All genes belonging to the same linkage group are inherited together during the formation of gametes.

In different linkage groups, the number of genes is not the same. Dihybrid interaction is characterized by the fact that such coupling does not obey. However, complete coupling is quite rare. As a rule, all four phenotypes are present in the offspring.

Allelic and Alleles are distinguished - these are forms of the same gene.

Allelic - the interaction of genes included in one allelic pair. The manifestation of a trait is determined not only by the relationship of dominance, but also by the number of genes in the genotype.

Allelic genes are able to create such connections as (when there is a product of only one gene in the phenotype of heterozygotes) and incomplete (the phenotype of heterozygotes differs from the phenotype of homozygotes in terms of and recessive, taking an average (intermediate) value in relation to them. Codominance is such an interaction of allelic genes, when heterozygotes in the phenotype possess the product of both.

Non-allelic - the joint influence of two (several) non-allelic genes. It can be expressed in the form of an epistatic, complementary, polymeric or modifying interaction.

The interaction of non-allelic genes can take place in different ways, therefore, several types are distinguished.

Complementary - the interaction of independently Mendelian genes in one genotype and causing the manifestation of any one trait.

Polymeric is the additive influence of a number of non-allelic genes on the formation of a certain trait, which causes a variational continuous series in terms of quantitative expression. Polymerism is cumulative and non-cumulative. In the first case, the manifestation of a trait is determined by the number of dominant alleles of polymeric genes that are contained in the genotype. In the second case, the degree of trait development is determined only by the presence of dominant alleles and does not depend on their number.

Epistatic - suppression of one gene by the dominant allele of another, non-allelic to the first. Or the suppression of the action of the dominant and recessive allele in the hypostatic allele of the epistatic allele, which is in the homozygous state.

Complementary - a trait develops with the mutual action of 2 dominant genes, which individually do not cause the development of a trait.

Modifying - changing the action of the main genes with non-allelic modifiers in relation to them. One gene can be the main one in controlling the development of some trait and a modifier in relation to the development of another trait.

The interaction of genes is always observed when several genes influence the formation of a certain state of any feature of the organism.

Allelic genes are paired, determining the development of mutually exclusive traits (tall and short stature, curly and smooth hair, blue and black eyes in humans).
1. Interaction of non-allelic genes: the development of a trait under the control of several genes is the basis of a new formation when crossing. Example: the appearance of gray rabbits (Aabb) when crossing black (Aab) and white (aaBB). The cause of the neoplasm: genes Aa are responsible for the color of the coat (A is black wool, a is white), genes Bb are responsible for the distribution of the pigment along the length of the hair (B - the pigment accumulates at the hair root, b - the pigment is evenly distributed along the length of the hair).
2. Multiple action of genes - the influence of one gene on the formation of a number of traits. Example: the gene responsible for the formation of red pigment in a flower contributes to its appearance in the stem, leaves, causes the lengthening of the stem, and an increase in the mass of seeds.

28. Genotype- a set of genes of a given organism, which, in contrast to the concepts of genome and gene pool, characterizes an individual, not a species.

Phenotype- a set of characteristics inherent in an individual at a certain stage of development. In diploid organisms, dominant genes appear in the phenotype.

Most genes appear in the phenotype of an organism, but the phenotype and genotype are different in the following ways:

1. According to the source of information (the genotype is determined by studying the DNA of an individual, the phenotype is recorded by observing the appearance of the organism).

2. The genotype does not always correspond to the same phenotype. Some genes appear in the phenotype only under certain conditions. On the other hand, some phenotypes, such as the color of animal fur, are the result of the interaction of several genes in the form of complementarity.

Variability- the ability of living organisms to acquire new features and properties. Due to variability, organisms can adapt to changing environmental conditions.

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

reaction rate- the ability of the genotype to form in ontogenesis, depending on environmental conditions, different phenotypes. It characterizes the share of participation of the environment in the implementation of the trait and determines the modification variability of the species.

29. Modifications called changes in the phenotype caused by the influence environment and not associated with changes in the genotype. All signs are subject to modification variability. The occurrence of modifications is due to the fact that such important environmental factors as light, heat, moisture, chemical composition and soil structure, air, affect the activity of enzymes and to a certain extent change the course of biochemical reactions occurring in a developing organism. Adaptive modifications enable the organism to survive and leave offspring in changing environmental conditions.

hereditary variability is divided into combinative and mutational. Variability is called combinative, which is based on the formation of recombinations, i.e. such combinations of genes that the parents did not have. Combinative variability is based on sexual reproduction organisms, resulting in a huge variety of genotypes. Mutation is the variability of the genotype itself. Mutations are sudden inherited changes in the genetic material, leading to a change in certain characteristics of the organism.

30. combinative called variability, which is based on the formation of recombinations, i.e. such combinations of genes that the parents did not have. Combinative variability is based on sexual reproduction of organisms, as a result of which a huge variety of genotypes arises. Three processes serve as almost unlimited sources of genetic variability:

Independent divergence of homologous chromosomes in the first meiotic division. (The appearance of green smooth and yellow wrinkled pea seeds in the second generation from crossing plants with yellow smooth and green wrinkled seeds is an example of combinative variability.)

Mutual exchange of sections of homologous chromosomes, or crossing over. It creates new linkage groups. Recombinant chromosomes, once in the zygote, contribute to the appearance of signs that are atypical for each of the parents.

Random combination of gametes during fertilization.

These sources of combinative variability operate independently and simultaneously, while providing a constant "shuffling" of genes, which leads to the emergence of organisms with a different genotype and phenotype.

Biological significance: provides an infinite variety of individuals within a species and the uniqueness of each of them.

The sexual process: recombination is the redistribution of the genetic material of the parents, as a result of which the offspring have new combinations of genes that determine new combinations of traits. Recombination is the basis of combinative variability. In eukaryotic organisms that reproduce sexually, recombination occurs during meiosis with independent divergence of chromosomes and with the exchange of homologous regions between homologous chromosomes (crossing over). Recombinations also occur in sex and, much less frequently, in somatic cells. Prokaryotes (bacteria) and viruses have special mechanisms for gene exchange. Thus, recombination is a universal way to increase genotypic variability in all organisms, creating material for natural selection.

Mutational called the variability of the genotype itself. Mutations are sudden inherited changes in the genetic material, leading to a change in certain characteristics of the organism.

Gene mutations- changes in the structure of genes. Since a gene is a section of a DNA molecule, a gene mutation is a change in the nucleotide composition of this section. Gene mutations can occur as a result of: 1) replacement of one or more nucleotides with others; 2) insertion of nucleotides; 3) loss of nucleotides; 4) nucleotide doubling; 5) changes in the order of alternation of nucleotides. These mutations lead to a change in the amino acid composition of the polypeptide chain and, consequently, to a change in the functional activity of the protein molecule.

Chromosomal mutations - changes in the structure of chromosomes. Rearrangements can be carried out both within the same chromosome - intrachromosomal mutations, and between chromosomes - interchromosomal mutations.

Genomic mutation called a change in the number of chromosomes. Genomic mutations result from disruption of the normal course of mitosis or meiosis.

Properties of mutations: it is currently believed that many mutations do not significantly affect the viability of individuals; such mutations are called neutral. The neutrality of mutations is often due to the fact that most of the mutant alleles are recessive with respect to the original allele. However, there are mutations that lead to the death of the organism (lethal) or significantly reduce its viability (semi-lethal). Under certain conditions, mutations can increase the viability of organisms (as in the example of sickle cell anemia).

According to the ability to be transmitted during sexual reproduction, somatic and generative mutations are distinguished. Somatic mutations do not affect germ cells and are not transmitted to descendants. Somatic mutations result in genetic mosaics. Generative mutations occur in germ cells and can be passed on to offspring. With the participation of mutant germ cells, completely mutant organisms are formed. The mutant allele can return to its original state. Then the initial mutation is called direct (for example, the transition A → a), and the other is called the reverse mutation, or reversion (for example, the reverse transition a → A).

The biological significance of mutations: First of all, mutations have an impact on evolution. It was the constant presence of mutations that was of decisive importance for the evolutionary development of species. In changing environmental conditions, the emergence of a mutation that gave rise to organisms better adapted to given conditions was at the same time a step forward.

Generating Mutations: Generally, mutagens are divided into three groups. For the artificial production of mutations, physical and chemical mutagens are used.

Ø Physical: X-rays, gamma rays, ultraviolet radiation, high and low temperatures, etc.

Ø Chemical: salts of heavy metals, alkaloids, foreign DNA and RNA, analogues of nitrogenous bases nucleic acids and etc.

Ø Biological: viruses, bacteria.

generative mutations arise in germ cells, do not affect the characteristics of this organism, appear only in the next generation.

Somatic mutations arise in somatic cells, appear in a given organism and are not transmitted to offspring during sexual reproduction. The only way to save somatic mutations is through asexual reproduction.

1. Complete dominance

2. incomplete dominance- weakening of the action of the dominant gene in the presence of a recessive one (at the same time, an intermediate character of the trait is observed in heterozygotes)

3. Overdominance - the dominant gene in the heterozygous state is more pronounced than in the homozygous state

4. co-dominance - the genes of one allelic pair are equivalent and if both are present in the genotype, then both show their effect (IV blood group)

5. interallelic complementation - a normal trait is formed as a result of a combination of two mutant genes in a heterozygote. The reason is that the products of recessive genes, interacting and complementing each other, form a trait identical to the activity of the dominant allele.

6. Allelic exclusion - a type of interaction in which one of the alleles of the gene is inactivated, which leads to the manifestation of different alleles in cells

10. Characteristics of the main types of interaction of non-allelic genes.

1. complementarity- a type of interaction in which a new trait arises from the interaction of two dominant non-allelic genes that are in the same genotype, while, being present in the genotype separately, they affect the trait in a different way.

Splits in F 2

2. epistasis- suppression of alleles of one gene by the action of alleles of other genes.

The repressive gene is called epistatic, the repressed gene is called hypostatic.

The epistatic interaction of non-allelic genes can be dominant (13:3, 12:3:1) and recessive (9:3:4).

3. Polymerism- several dominant non-allelic genes determine the same trait. Such genes are denoted by the same letters with different indices.

Polymeria happens:

Non-cumulative - it is not the number of dominant genes in the genotype that influences, but the presence of at least one (15: 1)

The human genotype includes a huge number of genes that carry information about the properties and qualities of our body. Despite such a large number, they interact as a single integrated system.

From school course biology, we know the laws of Mendel, who studied the patterns of inheritance of traits. In the course of his research, the scientist discovered dominant genes and recessive ones. Some are able to suppress the manifestation of others.

In fact, the interaction of genes goes far beyond the Mendelian laws, although all the rules of inheritance are observed. You can see the difference in the nature of splitting by phenotype, because the type of interaction may differ.

Gene characteristics

A gene is a unit of heredity, it has certain characteristics:

1. The gene is discrete. It determines the degree of development of a particular trait, including the features of biochemical reactions.
2. Has a gradual effect. Accumulating in the cells of the body, it can lead to an increase or decrease in the manifestation of a symptom.
3. All genes are strictly specific, that is, they are responsible for the synthesis of a particular protein.
4. One gene can have multiple effects, affecting the development of several traits at once.
5. Different genes can take part in the formation of one trait.
6. All genes can interact with each other.
7. The external environment influences the manifestation of the action of the gene.

Genes are able to act at two different levels. The first is the genetic system itself, which determines the state of the genes and their work, stability and variability. The second level can be considered already when working in the cells of the body.

Types of interaction of allelic genes

All cells in our body have a diploid set of chromosomes (it is also called double). The 23 chromosomes of the egg are fused with the same number of chromosomes of the sperm. That is, each trait is represented by two alleles, so they are called allelic genes.

Such allelic pairs are formed during fertilization. They can be either homozygous, that is, consisting of the same alleles, or heterozygous, if different alleles are included.

The forms of interaction of allelic genes are clearly presented in the table.

Type of interaction	The nature of the interaction	Example
Complete dominance	The dominant gene completely suppresses the manifestation of the recessive.	Inheritance of pea color, human eye color.
incomplete dominance	The dominant gene does not completely suppress the expression of the recessive gene.	Coloring of flowers in the night beauty (flower).
Codominance	In the heterozygous state, each of the allelic genes causes the development of a trait controlled by it.	Inheritance of blood group in humans.
overdominance	In the heterozygous state, the signs appear brighter than in the homozygous state.	A striking example is the phenomenon of heterosis in the animal and plant world, sickle cell anemia in humans.

Complete and incomplete dominance

We can speak of complete dominance when one of the genes can provide the manifestation of a trait, and the second is unable to do so. A strong gene is called dominant, and its opponent is called recessive.

Inheritance in this case occurs completely according to the laws of Mendel. For example, the color of pea seeds: in the first generation we see all green peas, that is, this color is a dominant feature.

If during fertilization the gene for brown eyes and blue eyes get together, then the child's eyes will be brown, because this allele completely suppresses the gene that is responsible for blue eyes.

With incomplete dominance, one can see the manifestation of an intermediate trait in heterozygotes. For example, when crossing a homozygous dominant nocturnal beauty with red flowers with the same individual, only with a white corolla, one can see hybrids in the first generation Pink colour. The dominant red trait does not completely suppress the manifestation of the recessive white, so in the end something in between is obtained.

Codominance and overdominance

Such an interaction of genes, in which each provides its own trait, is called codominance. All genes in one allelic pair are absolutely equivalent. Neither can suppress the action of the other. It is this interaction of genes that we observe in the inheritance of blood groups in humans.

Gene O provides the manifestation of the 1st blood group, gene A - the second, gene B - the third, and if genes A and B fall together, then none can suppress the manifestation of the other, therefore a new sign is formed - the 4th blood group.

Overdominance is another example of the interaction of allelic genes. In this case, heterozygous individuals for this trait have a more pronounced manifestation of it compared to homozygous individuals. This interaction of genes underlies such a phenomenon as heterosis (the phenomenon of hybrid strength).

When two tomato varieties are crossed, for example, a hybrid is obtained that inherits the traits of both original organisms, since the traits become heterozygous. In the next generation, splitting according to traits will already begin, so it will not be possible to obtain the same offspring.

In the animal world one can even observe the barrenness of such hybrid forms. Such examples of gene interaction can often be found. For example, when a donkey and a mare are crossed, a mule is born. He inherited everything best qualities his parents, but he himself cannot have offspring.

In humans, sickle cell anemia is inherited by this type.

Non-allelic genes and their interaction

Genes that are located on different pairs of chromosomes are called non-allelic. If they are together, they may well influence each other.

The interaction of non-allelic genes can be carried out in different ways:

1. Complementarity.
2. Epistasis.
3. polymer action.
4. Pleiotropy.

All these types of gene interaction have their own distinctive features.

complementarity

In this interaction, one dominant gene complements another, which is also dominant, but not allelic. Getting together, they contribute to the manifestation of a completely new feature.

An example of the manifestation of color in sweet pea flowers can be given. The presence of pigment, which means that the color of the flower is provided by a combination of two genes - A and B. If at least one of them is absent, then the corolla will be white.

In humans, such an interaction of non-allelic genes is observed during the formation of the hearing organ. Normal hearing can be only if both genes - D and E - are present in the dominant state. In the presence of only one dominant or both in a recessive state, hearing is absent.

epistasis

This interaction of non-allelic genes is completely opposite to the previous interaction. In this case, one non-allelic gene is able to suppress the manifestation of another.

The forms of gene interaction in this variant can be different:

• dominant epistasis.
• Recessive.

In the first type of interaction, one dominant gene suppresses the manifestation of another dominant one. Recessive genes are involved in recessive epistasis.

According to this type of interaction, the color of the fruit in the pumpkin is inherited, the color of the coat in horses.

Polymer action of genes

This phenomenon can be observed when several dominant genes are responsible for the manifestation of the same trait. If at least one dominant allele is present, then the trait will definitely appear.

The types of gene interaction in this case can be different. One of them is storage polymer, when the degree of manifestation of a trait depends on the number of dominant alleles. This is how the color of wheat grains or the color of the skin in humans is inherited.

Everyone knows that all people have different skin colors. For some, it is completely light, some have dark skin, and representatives of the Negroid race are completely black. Scientists are of the opinion that skin color is determined by the presence of three different genes. For example, if the genotype contains all three in a dominant state, then the skin is the darkest, like that of blacks.

In the Caucasian race, judging by the color of our skin, there are no dominant alleles.

It has long been found that the interaction of non-allelic genes by the type of polymer affects most of the quantitative traits in humans. These include: height, body weight, intellectual abilities, body resistance to infectious diseases, and some others.

It can only be noted that the development of such traits depends on environmental conditions. A person may be predisposed to overweight, but if you follow the diet, it is possible to avoid this problem.

Pleiotropic action of genes

Scientists have long been convinced that the types of gene interaction are rather ambiguous and very versatile. Sometimes it is impossible to predict the manifestation of certain phenotypic traits, because it is not known how genes interact with each other.

This statement is only emphasized by the fact that one gene can influence the formation of several traits, that is, have a pleiotropic effect.

It has long been noted that the presence of red pigment in beet fruits is necessarily accompanied by the presence of the same, but only in the leaves.

In humans, a disease such as Marfan's syndrome is known. It is associated with a defect in the gene that is responsible for the development of connective tissue. As a result, it turns out that wherever this tissue is in the body, problems can be observed.

Such patients have long "spider" fingers, a dislocation of the lens of the eye, a heart disease are diagnosed.

The influence of environmental factors on the action of genes

The influence of external environmental factors on the development of organisms cannot be denied. These include:

• Nutrition.
• temperature.
• Light.
• The chemical composition of the soil.
• Humidity, etc.

Environmental factors are fundamental in the processes of selection, heredity and variability.

When we consider the forms of interaction of allelic or non-allelic genes, we must always take into account the influence of the environment. An example can be given: if primrose plants are crossed at a temperature of 15-20 degrees, then all hybrids of the first generation will have a pink color. At a temperature of 35 degrees, all plants will turn out white. So much for the influence of the environmental factor on the manifestation of signs, it does not matter here which gene is dominant. In rabbits, it turns out that the color of the coat also depends on the temperature factor.

Scientists have long been working on the question of how to control the manifestations of signs by exerting various external influences. This may provide an opportunity to control the development of congenital traits, which is especially relevant for humans. Why not use your knowledge to prevent certain hereditary ailments from manifesting?

All types of interaction of allelic genes, and not only them, can be so different and multifaceted that it is impossible to attribute them to any particular type. Only one thing can be said, that all these interactions are equally complex both in humans and in representatives of all species of plants and animals.

Both alleles - both dominant and recessive - show their effect, i.e. the dominant allele does not completely suppress the action of the recessive allele (intermediate effect of action) Cleavage by phenotype in F 2 1:2:1 Interaction of allelic genes Incomplete dominance

When codominating (a heterozygous organism contains two different dominant alleles, for example, A1 and A2 or J A and J B), each of the dominant alleles shows its effect, i.e. involved in the expression of the trait. Phenotype splitting in F 2 1:2:1 Interaction of allelic genes Codominance

An example of codominance is the IV human blood group in the ABO system: genotype - J A, J B, phenotype - AB, i.e. in people with IV blood group, both antigen A (according to the J A gene program) and antigen B (according to the J B gene program) are synthesized in erythrocytes. P x II group III group G JAJA J0J0 JBJB J0J0 J A J 0 J B J 0 F1F1 J A J 0 J A J B J B J 0 J 0 II group IV group III group I group

Suppression of the manifestation of the genes of one allelic pair by the genes of another. Genes that suppress the action of other non-allelic genes are called suppressors (suppressors). Dominant epistasis (phenotype splitting 13:3) and recessive (phenotype splitting 9:3:4) Epistasis Interaction of non-allelic genes

Problem If a black woman (A1A1A2A2) and a white man (a1 a1 a2 a2) have children, then what proportion can be expected to have children - complete blacks, mulattoes and whites? Solution of the problem Designation of genes: A1, A2 genes that determine the presence of pigment a 1, and 2 genes that determine the absence of pigment