8. BODY SCHEME AND INTERNAL REPRESENTATION SYSTEM Currently, most experts agree that the interaction of the body with the external environment is based on a model of the external world and a model of one’s own body, built by the brain. The need for internal models

In 1988 in the USA, on the initiative of Nobel Prize winner James Watson, and in 1989 in Russia, under the leadership of academician Alexander Aleksandrovich Baev, work began on the implementation of the grandiose world project “Human Genome”. In terms of the scale of funding, this project is comparable to space projects. The goal of the first stage of work was to determine the complete sequence of nucleotides in human DNA. Hundreds of scientists from many countries around the world have been working on solving this problem for 10 years. All chromosomes were “divided” between scientific teams of the countries participating in the project. Russia received the third, thirteenth and nineteenth chromosomes for research.

In the spring of 2000, the results of the first stage were summed up in the Canadian city of Vancouver. It was officially announced that the nucleotide sequence of all human chromosomes had been deciphered. It is difficult to overestimate the importance of this work, since knowledge of the structure of the genes of the human body allows us to understand the mechanisms of their functioning and, therefore, determine the influence of heredity on the formation of the characteristics and properties of the body, on health and life expectancy. During the research, many new genes were discovered, whose role in the formation of the body will need to be studied in more detail in the future. The study of genes leads to the creation of fundamentally new diagnostic tools and methods of treating hereditary diseases. Decoding the human DNA sequence is of great practical importance for determining genetic compatibility during 1 organ transplant, for genetic fingerprinting and genotyping.

But the information obtained was important not only for biology and medicine. Based on knowledge of the structure of the human genome, it is possible to reconstruct the history of human society and the evolution of man as a biological species. Comparing the genomes of different species of organisms allows us to study the origin and evolution of life on Earth.

What is the human genome?

■ Human genome. You already know the concepts of “gene” and “genotype”. The term " genome"was first introduced by the German botanist Hans Winkler in 1920, who characterized it as a set of genes characteristic of the haploid set of chromosomes of a given species of organism. Unlike the genotype, the genome is a characteristic of the species, not a separate one | individuals. Each gamete of a diploid organism, carrying a haploid set of chromosomes, essentially contains a genome characteristic of that species. Remember the inheritance of traits in peas. Every plant has genes for seed color, seed shape, and flower color; they are mandatory for its existence and are included in the genome of this species. But in any pea plant, like in all diploid organisms, there are two alleles for each gene, located on homologous chromosomes. In one plant, these may be the same alleles responsible for the yellow color of peas, in another - different, causing yellow and green, in a third - both alleles will determine the development of green color of seeds, and so on for all characteristics. These individual differences are characteristic genotype a specific individual, not a genome. So, the genome is a “list” of genes necessary for the normal functioning of the body.

Decoding the complete sequence of nucleotides in human DNA has made it possible to estimate the total number of genes that make up the genome. It turned out that there are only about 30-40 thousand of them, although the exact number is not yet known. Previously, it was assumed that the number of genes in a person is 3-4 times more, about 100 thousand, so these results became a kind of sensation. Each of us has only 5 times more genes than yeast, and only 2 times more than Drosophila. Compared to other organisms, we don't have many genes. Maybe there are some features in the structure and functioning of our genome that allow a person to be a complex creature?

■ The structure of the eukaryotic gene. On average, there are about 50 thousand nucleotides per gene in a human chromosome. There are very short genes. For example, the protein enkephalin, which is synthesized in neurons of the brain and affects the formation of our positive emotions, consists of only 5 amino acids. Consequently, the gene responsible for its synthesis contains only about two dozen nucleotides. And the longest gene, encoding one of the muscle proteins, consists of 2.5 million nucleotides.

In the human genome, as well as in other mammals, protein-coding DNA regions account for less than 5% of the total chromosome length. The rest, most of the DNA, was previously called redundant, but now it has become clear that it performs very important regulatory functions, determining in which cells and when certain genes should function. In more simply organized prokaryotic organisms, the genome of which is represented by one circular DNA molecule, the coding part accounts for up to 90% of the entire genome.

All tens of thousands of genes do not work simultaneously in every cell of a multicellular organism; this is not required. The existing specialization between cells is determined by the selective functioning of certain genes. A muscle cell does not need to synthesize keratin, and a nervous cell does not need to synthesize muscle proteins. Although it should be noted that there is a fairly large group of genes that work almost constantly in all cells. These are genes that encode information about proteins necessary for vital cell functions, such as reduplication, transcription, ATP synthesis and many others.

In accordance with modern scientific concepts, a gene in eukaryotic cells encoding a specific protein always consists of several required elements. As a rule, at the beginning and at the end of the gene there are special regulatory regions; they determine when, under what circumstances and in what tissues this gene will work. Such regulatory regions can additionally be located outside the gene, located quite far away, but, nevertheless, actively participating in its control.

In addition to the regulatory zones, there is a structural part of the gene, which actually contains information about the primary structure of the corresponding protein. In most eukaryotic genes it is significantly shorter than the regulatory zone.

■ Gene interaction. It is necessary to clearly understand that the work of one gene cannot be carried out in isolation from all the others. The mutual influence of genes is diverse, and in the formation of most of the characteristics of an organism, not one or two, but dozens of different genes usually take part, each of which makes its own specific contribution to this process.

According to the Human Genome Project, the normal development of a smooth muscle cell requires the coordinated work of 127 genes, and the products of 735 genes are involved in the formation of striated muscle fiber.

As an example of gene interaction, consider how flower color is inherited in some plants. In the cells of the corolla of sweet peas, a certain substance is synthesized, the so-called propigment, which, under the action of a special enzyme, can turn into anthocyanin pigment, causing the purple color of the flower. This means that the presence of color depends on the normal functioning of at least two genes, one of which is responsible for the synthesis of propigment, and the other for the synthesis of the enzyme. A disruption in the functioning of any of these genes will lead to a disruption in pigment synthesis and, as a result, to a lack of color; in this case, the corolla of the flowers will be white.

Sometimes the opposite situation occurs, when one gene influences the development of several traits and properties of the organism. This phenomenon is called pleiotropy or multiple gene action. As a rule, such an effect is caused by genes whose functioning is very important in the early stages of ontogenesis. In humans, a similar example is a gene involved in the formation of connective tissue. A disruption in its functioning leads to the development of several symptoms at once: long “spider” fingers, very high growth due to strong elongation of the limbs, high joint mobility, disruption of the structure of the lens and aneurysm (protrusion of the wall) of the aorta.

■ Interaction of nonallelic genes. Several types of interaction of non-allelic genes are known.

Complementary interaction. The phenomenon of interaction of several non-allelic genes, leading to the development of a new manifestation of a trait that is absent in the parents, is called complementary interaction. The example of inheritance of flower color in sweet peas, given in §-3.14, refers precisely to this type of gene interaction. The dominant alleles of two genes (A and B), each individually, cannot provide pigment synthesis. The anthocyanin pigment, which causes the purple color of the flower, begins to be synthesized only when dominant alleles of both genes (A - B -) are present in the genotype.

A well-known example of complementary interaction is the inheritance of comb shape in chickens. There are four forms of comb, the formation of which is determined by the interaction of two non-allelic genes - A and B. If the genotype contains dominant alleles of only gene A (A_bb), a rose-shaped comb is formed, the presence of dominant alleles of the second gene B (aaB_) causes the formation of a pea-shaped comb. If the genotype contains dominant alleles of both genes (A_B_), a nut-shaped comb is formed, and in the absence of dominant alleles (aabb), a simple comb develops.

Epistasis. The interaction of non-allelic genes, in which the gene of one allelic pair suppresses the expression of the gene of another allelic pair, is called epistasis. Genes that suppress the action of other genes are called inhibitors or suppressors. Inhibitor genes can be either dominant (I) or recessive (i), therefore, dominant and recessive epistasis are distinguished.

At dominant epistasis one dominant gene (I) suppresses the expression of another non-allelic dominant gene.

There are two possible variants of phenotypic cleavage in dominant epistasis.

1. Homozygotes for recessive alleles (aa/7) do not differ phenotypically from organisms that have dominant alleles of the inhibitor gene in their genotype.

In pumpkin, the color of the fruit can be yellow (A) or green (a). The manifestation of this color can be suppressed by a dominant inhibitor gene (I), resulting in the formation of white fruits (A_I_; aaI_).

white green

F 2: 9/16 A_I_; 3/16 A_ii ; 3/16

white (12) yellow (3) green (1)

In the described and similar cases, when splitting in F 2 according to the 9:3:3:1 genotype, the phenotypic splitting corresponds to 12:3:1.

2. Homozygotes for recessive alleles (aaii) do not differ in phenotype from organisms with genotypes A_I_ and aaI_.

In corn, the structural gene A determines the color of the grain: purple (A) or white (a). In the presence of a dominant allele of the inhibitor gene (I), the pigment is not synthesized.

R: AAII x aaii

white white

F 2:9/16 A_I_; 3/16 aaI_; 1/16 aaii 3/16A_ii

white (13) purple (3)

In F 2, 9/16 plants (A_I_) do not synthesize pigment, because the genotype contains a dominant allele of the inhibitor gene (I). In 3/16 plants (aaI_), the grain color is white, since in their genotype there is no dominant allele A, responsible for pigment synthesis, and in addition there is a dominant allele of the inhibitor gene. In 1/16 plants (aaii), the grains are also white, because their genotype does not have the dominant allele A, which is responsible for the synthesis of purple pigment. Only 3/16 plants with the A_ii genotype develop colored (purple) grains, since in the presence of the dominant allele A, their genotype does not have a dominant allele of the inhibitor gene.

In this and other similar examples, the phenotypic cleavage in F 2 is 13:3. (Please note that according to the genotype, the splitting still remains the same - 9: 3: 3: 1, corresponding to the splitting in a dihybrid cross.)

At recessive epistasis a recessive allele of an inhibitor gene in a homozygous state suppresses the manifestation of a non-allelic dominant gene.

In flax, the B gene determines the pigmentation of the corolla: allele B - blue corolla, allele b - pink. Color develops only if there is a dominant allele of another non-allelic gene in the genotype - I. The presence of two recessive alleles ii in the genotype leads to the formation of an uncolored (white) corolla.

pink white

F 2: 9/16 B_I_; 3/16 bbI_; 3/16B_ii; 1/16bbii

Blue (9) pink (3) white (4)

With recessive epistasis in this and other similar cases in F 2, a splitting according to the 9:3:4 phenotype is observed.

■ Polymer action of genes (polymerism). Another option for the interaction of non-allelic genes is polymerization. With this interaction, the degree of expression of a trait depends on the number of dominant alleles of these genes in the genotype: the more dominant alleles in the sum, the more strongly the trait is expressed. An example of such a polymer interaction is the inheritance of grain color in wheat. Plants with genotype A 1 A 1 A 2 A 2 have dark red grains, plants a 1 a 1 a 2 a 2- white grains, and plants with one, two or three dominant alleles - varying degrees of color: from pink to red. This polymer is called cumulative or cumulative.

However, there are options and non-cumulative polymer. For example, inheritance of the shape of a pod in a shepherd's purse is determined by two non-allelic genes - A 1 and A 2. If there is at least one dominant allele in the genotype, a triangular pod shape is formed; in the absence of dominant alleles (a 1 a 1 a 2 a 2), the pod has an oval shape. In this case, the phenotypic split in the second generation will be 15:1.

R:a 1 a 1 a 2 a 2 x a 1 a 1 a 2 a 2

triangle oval shape

F 1:A 1 a 1 A 2 a 2

triangle form

F 2:9/16A 1 _A 2 _; 3/16A 1 _a 2 a 2 ; 3/16a 1 a 1 A 2 _; 1/16a 1 a 1 a 2 a 2

triangle triangle triangulated.

form (9) form (3) form (3) form (1)

triangle oval

shape (15/16) shape (1/16)

“Regularities of monohybrid crossing” - Analyzing crosses. Inheritance of pea flower color. Cytological (cytogenetic) basis of inheritance of traits. Monohybrid crossing. Inheritance of strawberry color. Return crosses. Dominant variant of the trait. First generation hybrids. Saturating crosses. Incomplete dominance. Inheritance of pea seed color.

"Morgan's Chromosome Theory" - Disruption of gene linkage. Tomato chromosomes. Crossing pure Drosophila lines. Crossing hybrids. Law of adhesion. Females and males. Clutch group. Chromosomal theory of heredity. Morganida. Crossover frequency. Prophase I of meiosis. Linked genes. Drosophila fly. Experiments by T. Morgan. Morgan. Section of the genetic map. Second generation hybrids. Chromosome theory. Crossover offspring. Genetic map.

"Morgan's Law" - In what cases is Morgan's law fulfilled? Non-crossover gametes. The probability of two genes diverging on different chromosomes. Dominant genes for cataract, elliptocytosis and polydactylism. 1% crossing over. Clutch group. The linkage of genes can be disrupted during the process of crossing over. Complete grip tasks. The appearance of individuals with recombined characters. Recombined features. Genes localized on the same chromosome.

“Interaction of non-allelic genes” - Additive polymer. Terms. Presence of pigment. Dominant epistasis. Polymeric interaction of genes. Split. Interaction of nonallelic genes. Phenotype splitting. Complementary interaction. Types of interaction of non-allelic genes. Color intensity. Dominant epistasis using the example of color inheritance in horses. Rose-shaped comb. Epistatic interaction of genes. Recessive epistasis as exemplified by the inheritance of coloration in mice.

“Pedigree” - Goals and objectives of the study. Blood groups. Pedigree. Family pedigree. The pedigree shows an autosomal recessive type of inheritance. Inheritance of blood groups in humans. Genealogical method of human genetics. Hair color. Inheritance of hair shape. Hair shape. Pedigree analysis. Inability to distinguish individual colors.

“Mendelian Genetics” - Basics of genetics. Atmosphere of cooperation. Conclusions. Phenotype. Problem using Mendel's 3rd law. Dihybrid crossing. Mendel's third law. Longhair. Gregor Mendel. Illustrations of Mendel's first and second laws.

Question 1. What is a genome?

A genome is a set of genes characteristic of the haploid set of chromosomes of a given biological species. The genome, in contrast to the genotype, is a characteristic of a species, not an individual, since it describes a set of genes characteristic of a given species, and not their alleles, which determine the individual differences of individual organisms. The degree of similarity between the genomes of different species reflects their evolutionary relatedness.

Question 2. What determines the existing specialization of cells?

The specialization of body cells is determined by the selective functioning of genes. In each cell, genes work that are characteristic specifically for a given type of tissue and organ: in muscle cells - genes for muscle proteins, in cells of the stomach walls - genes for digestive enzymes, etc. Most other genes are blocked. , and their activation can lead to the development of serious diseases (for example, the appearance of a cancerous tumor).

Question 3. What essential elements are included in the gene of a eukaryotic cell?

The obligatory elements of a eukaryotic gene are:

• regulatory regions located at the beginning and end of the gene, and also sometimes outside the gene (at some distance from it). They determine when, under what circumstances and in what types of tissues this gene will work;
• structural part, which contains information about the primary structure of the encoded protein; usually the structural part is smaller than the regulatory part.

Question 4. Give examples of gene interaction.Material from the site

An example of gene interaction is the pigmentation (color) of a rabbit's fur. The formation of a certain color is regulated by two genes. One of them (let's call it A) is responsible for the presence of pigment, and if the work of this gene is disrupted (recessive allele), the rabbit's fur will be white (genotype aa). The second gene (let's call it B) is responsible for the uneven coloring of the coat. In the case of normal functioning of this gene (dominant allele), the synthesized pigment accumulates at the base of the hair, and the rabbit has a gray color (genotypes AaBb, AAVb, AaBB, AABB). If the second gene is represented only by recessive alleles, then the synthesized pigment is distributed evenly. These rabbits have black fur (genotypes Aavv, AAvv).

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Question 1. What is a genome?
Genome is a set of genes characteristic of the haploid set of chromosomes of a given biological species. The genome, in contrast to the genotype, is a characteristic of a species, not an individual, since it describes a set of genes characteristic of a given species, and not their alleles, which determine the individual differences of individual organisms. The degree of similarity between the genomes of different species reflects their evolutionary relatedness.
Question 2. What determines the existing specialization of cells?
The specialization of body cells is determined by the selective functioning of genes. In each cell, genes work that are characteristic specifically for a given type of tissue and organ: in muscle cells - genes for muscle proteins, in cells of the stomach walls - genes for digestive enzymes, etc. Most other genes are blocked, and their activation can lead to the development serious diseases (for example, the appearance of a cancerous tumor).

Question 3. What essential elements are included in the gene of a eukaryotic cell?
The obligatory elements of a eukaryotic gene are:
1. regulatory regions located at the beginning and end of the gene, and also sometimes outside the gene (at some distance from it). They determine when, under what circumstances and in what types of tissues this gene will work (left, intermediate and right regulatory elements).
2. a section of DNA encoding the primary transcript, including the nucleotide sequence found in RNA molecules; introns (for mRNA), intermediate sequences - spacers (for rRNA). Introns and spacers are removed during processing of primary transcripts; untranslated nucleotide sequences.
3. Minimum sequences required for the start of transcription (promoter) and the end of transcription (terminator).
4. Sequences regulating the frequency of transcription initiation; responsible for inducibility and repression of transcription, as well as cellular, tissue and temporal specificity of transcription. They are diverse in structure, position and functions.
5. These include enhancers (from the English enhance - to strengthen) and silencers (from the English silence - to drown out) - these are DNA sequences located thousands of nucleotide pairs from the promoter of a eukaryotic gene and have a remote influence on its transcription.
6. DNA sequences are included that influence the spatial configuration of the gene in chromatin, sequences that regulate its topology.
The figure (Fig. 3) shows a diagram of the structure of a eukaryotic gene responsible for encoding protein synthesis.

Rice. 3. Structure of a eukaryotic gene encoding a protein.
+1 - transcription initialization point; 5" - NTR and 3" - NTR:
5" and 3" are untranslated sequences.

Question 4. Give examples of gene interaction.
An example of gene interaction is the pigmentation (color) of a rabbit's coat. The formation of a certain color is regulated by two genes. One of them (let's call it A) is responsible for the presence of pigment, and if the work of this gene is disrupted (recessive allele), the rabbit's fur will be white (genotype aa). The second gene (let's call it B) is responsible for the uneven coloration of the coat. In the case of normal functioning of this gene (dominant allele), the synthesized pigment accumulates at the base of the hair, and the rabbit has a gray color (genotypes AaBb, AABb, AaBB, AABB). If the second gene is represented only by recessive alleles, then the synthesized pigment is distributed evenly. These rabbits have black fur (genotypes Aabb, AAbb).