Biosynthesis of protein and nucleic acids. Genes, genetic code. Degeneracy of the genetic code: general information The universality of the genetic code lies in the fact that

In any cell and organism, all anatomical, morphological and functional features are determined by the structure of the proteins that comprise them. The hereditary property of the body is the ability to synthesize certain proteins. Amino acids are located in a polypeptide chain, on which biological characteristics depend.
Each cell has its own sequence of nucleotides in the polynucleotide chain of DNA. This is the genetic code of DNA. Through it, information about the synthesis of certain proteins is recorded. This article describes what the genetic code is, its properties and genetic information.

A little history

The idea that there might be a genetic code was formulated by J. Gamow and A. Down in the mid-twentieth century. They described that the nucleotide sequence responsible for the synthesis of a particular amino acid contains at least three units. Later they proved the exact number of three nucleotides (this is a unit of genetic code), which was called a triplet or codon. There are sixty-four nucleotides in total, because the acid molecule where RNA occurs is made up of four different nucleotide residues.

What is genetic code

The method of encoding the sequence of amino acid proteins due to the sequence of nucleotides is characteristic of all living cells and organisms. This is what the genetic code is.
There are four nucleotides in DNA:

• adenine - A;
• guanine - G;
• cytosine - C;
• thymine - T.

They are denoted by capital Latin or (in Russian-language literature) Russian letters.
RNA also contains four nucleotides, but one of them is different from DNA:

• adenine - A;
• guanine - G;
• cytosine - C;
• uracil - U.

All nucleotides are arranged in chains, with DNA having a double helix and RNA having a single helix.
Proteins are built on where they, located in a certain sequence, determine its biological properties.

Properties of the genetic code

Tripletity. A unit of genetic code consists of three letters, it is triplet. This means that the twenty amino acids that exist are encoded by three specific nucleotides called codons or trilpets. There are sixty-four combinations that can be created from four nucleotides. This amount is more than enough to encode twenty amino acids.
Degeneracy. Each amino acid corresponds to more than one codon, with the exception of methionine and tryptophan.
Unambiguity. One codon codes for one amino acid. For example, in a healthy person's gene with information about the beta target of hemoglobin, a triplet of GAG and GAA encodes A in everyone who has sickle cell disease, one nucleotide is changed.
Collinearity. The sequence of amino acids always corresponds to the sequence of nucleotides that the gene contains.
The genetic code is continuous and compact, which means that it has no punctuation marks. That is, starting at a certain codon, continuous reading occurs. For example, AUGGGUGTSUUAAUGUG will be read as: AUG, GUG, TSUU, AAU, GUG. But not AUG, UGG and so on or anything else.
Versatility. It is the same for absolutely all terrestrial organisms, from humans to fish, fungi and bacteria.

Table

Not all available amino acids are included in the table presented. Hydroxyproline, hydroxylysine, phosphoserine, iodine derivatives of tyrosine, cystine and some others are absent, since they are derivatives of other amino acids encoded by m-RNA and formed after modification of proteins as a result of translation.
From the properties of the genetic code it is known that one codon is capable of encoding one amino acid. The exception is the genetic code that performs additional functions and encodes valine and methionine. The mRNA, being at the beginning of the codon, attaches t-RNA, which carries formylmethione. Upon completion of the synthesis, it is cleaved off and takes the formyl residue with it, transforming into a methionine residue. Thus, the above codons are the initiators of the synthesis of the polypeptide chain. If they are not at the beginning, then they are no different from the others.

Genetic information

This concept means a program of properties that is passed down from ancestors. It is embedded in heredity as a genetic code.
The genetic code is realized during protein synthesis:

• messenger RNA;
• ribosomal rRNA.

Information is transmitted through direct communication (DNA-RNA-protein) and reverse communication (medium-protein-DNA).
Organisms can receive, store, transmit it and use it most effectively.
Passed on by inheritance, information determines the development of a particular organism. But due to interaction with the environment, the reaction of the latter is distorted, due to which evolution and development occur. In this way, new information is introduced into the body.

The calculation of the laws of molecular biology and the discovery of the genetic code illustrated the need to combine genetics with Darwin's theory, on the basis of which a synthetic theory of evolution emerged - non-classical biology.
Darwin's heredity, variation and natural selection are complemented by genetically determined selection. Evolution is realized at the genetic level through random mutations and the inheritance of the most valuable traits that are most adapted to the environment.

Decoding the human code

In the nineties, the Human Genome Project was launched, as a result of which genome fragments containing 99.99% of human genes were discovered in the two thousandths. Fragments that are not involved in protein synthesis and are not encoded remain unknown. Their role remains unknown for now.

Last discovered in 2006, chromosome 1 is the longest in the genome. More than three hundred and fifty diseases, including cancer, appear as a result of disorders and mutations in it.

The role of such studies cannot be overestimated. When they discovered what the genetic code is, it became known according to what patterns development occurs, how the morphological structure, psyche, predisposition to certain diseases, metabolism and defects of individuals are formed.

Genetic code– a system for recording genetic information in DNA (RNA) in the form of a certain sequence of nucleotides. A certain sequence of nucleotides in DNA and RNA corresponds to a certain sequence of amino acids in the polypeptide chains of proteins. It is customary to write the code using capital letters of the Russian or Latin alphabet. Each nucleotide is designated by the letter with which the name of the nitrogenous base included in its molecule begins: A (A) - adenine, G (G) - guanine, C (C) - cytosine, T (T) - thymine; in RNA instead of thyminuracil - U (U). The nucleotide sequence determines the sequence of incorporation of AK into the synthesized protein.

Properties of the genetic code:

1. Triplety- a meaningful unit of code is a combination of three nucleotides (triplet, or codon).
2. Continuity- there are no punctuation marks between triplets, that is, the information is read continuously.
3. Non-overlapping- the same nucleotide cannot simultaneously be part of two or more triplets (not observed for some overlapping genes of viruses, mitochondria and bacteria that encode several frameshift proteins).
4. Unambiguity(specificity) - a specific codon corresponds to only one amino acid (however, the UGA codon in Euplotescrassus encodes two amino acids - cysteine ​​and selenocysteine)
5. Degeneracy(redundancy) - several codons can correspond to the same amino acid.
6. Versatility- the genetic code works the same in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section “Variations of the standard genetic code” below).

Biosynthesis conditions

Protein biosynthesis requires genetic information from the DNA molecule; messenger RNA - the carrier of this information from the nucleus to the place of synthesis; ribosomes - organelles where protein synthesis itself occurs; a set of amino acids in the cytoplasm; transfer RNAs that encode amino acids and transfer them to the site of synthesis on ribosomes; ATP is a substance that provides energy for the encoding and biosynthesis process.

Stages

Transcription- the process of biosynthesis of all types of RNA on a DNA matrix, which occurs in the nucleus.

A certain section of the DNA molecule despirals, the hydrogen bonds between the two chains are destroyed under the action of enzymes. On one DNA strand, as on a template, an RNA copy is synthesized from nucleotides according to the complementary principle. Depending on the DNA section, ribosomal, transport, and messenger RNAs are synthesized in this way.

After mRNA synthesis, it leaves the nucleus and is sent to the cytoplasm to the site of protein synthesis on ribosomes.

Broadcast- the process of synthesis of polypeptide chains carried out on ribosomes, where mRNA is an intermediary in transmitting information about the primary structure of the protein.

Protein biosynthesis consists of a series of reactions.

1. Activation and coding of amino acids. tRNA has the shape of a clover leaf, in the central loop of which there is a triplet anticodon, corresponding to the code for a specific amino acid and the codon on the mRNA. Each amino acid is connected to the corresponding tRNA using the energy of ATP. A tRNA-amino acid complex is formed, which enters the ribosomes.

2. Formation of the mRNA-ribosome complex. mRNA in the cytoplasm is connected by ribosomes on the granular ER.

3. Assembly of the polypeptide chain. tRNA with amino acids, according to the principle of anticodon-codon complementarity, combines with mRNA and enters the ribosome. In the peptide center of the ribosome, a peptide bond is formed between two amino acids, and the released tRNA leaves the ribosome. In this case, the mRNA advances one triplet each time, introducing a new tRNA - an amino acid and removing the released tRNA from the ribosome. The entire process is provided by ATP energy. One mRNA can combine with several ribosomes, forming a polysome, where many molecules of one protein are simultaneously synthesized. Synthesis ends when nonsense codons (stop codes) begin on the mRNA. Ribosomes are separated from mRNA, and polypeptide chains are removed from them. Since the entire synthesis process takes place on the granular endoplasmic reticulum, the resulting polypeptide chains enter the ER tubules, where they acquire their final structure and are converted into protein molecules.

All synthesis reactions are catalyzed by special enzymes with the expenditure of ATP energy. The rate of synthesis is very high and depends on the length of the polypeptide. For example, in the ribosome of Escherichia coli, a protein of 300 amino acids is synthesized in approximately 15-20 seconds.

Genetic code– a unified system for recording hereditary information in nucleic acid molecules in the form of a nucleotide sequence. The genetic code is based on the use of an alphabet consisting of only four letters A, T, C, G, corresponding to DNA nucleotides. There are only 20 types of amino acids. Of the 64 codons, three - UAA, UAG, UGA - do not code for amino acids; they were called nonsense codons and serve as punctuation marks. Codon (encoding trinucleotide) is a unit of genetic code, a trio of nucleotide residues (triplet) in DNA or RNA, encoding the inclusion of one amino acid. The genes themselves do not take part in protein synthesis. The mediator between gene and protein is mRNA. The structure of the genetic code is characterized by the fact that it is triplet, that is, it consists of triplets (triples) of nitrogenous DNA bases, called codons. Out of 64

Properties of the gene. code
1) Triplety: one amino acid is encoded by three nucleotides. These 3 nucleotides in DNA
are called triplet, in mRNA - codon, in tRNA - anticodon.
2) Redundancy (degeneracy): there are only 20 amino acids, and there are 61 triplets encoding amino acids, so each amino acid is encoded by several triplets.
3) Uniqueness: each triplet (codon) encodes only one amino acid.
4) Universality: the genetic code is the same for all living organisms on Earth.
5.) continuity and indisputability of codons during reading. This means that the nucleotide sequence is read triplet by triplet without gaps, and adjacent triplets do not overlap each other.

88. Heredity and variability are fundamental properties of living things. Darwin's understanding of the phenomena of heredity and variability.
Heredity call the general property of all organisms to preserve and transmit characteristics from parent to offspring. Heredity- this is the property of organisms to reproduce in generations a similar type of metabolism that has developed during the historical development of the species and manifests itself under certain environmental conditions.
Variability is the process of the emergence of qualitative differences between individuals of the same species, which is expressed either in a change under the influence of the external environment of only one phenotype, or in genetically determined hereditary variations resulting from combinations, recombinations and mutations that take place in a number of successive generations and populations.
Darwin's understanding of heredity and variability.
Under heredity Darwin understood the ability of organisms to preserve their species, varietal and individual characteristics in their offspring. This feature was well known and represented hereditary variation. Darwin analyzed in detail the importance of heredity in the evolutionary process. He drew attention to cases of same-suit hybrids of the first generation and splitting of characters in the second generation; he was aware of heredity associated with sex, hybrid atavisms and a number of other phenomena of heredity.
Variability. When comparing many breeds of animals and varieties of plants, Darwin noticed that within any species of animals and plants, and in culture, within any variety and breed there are no identical individuals. Darwin concluded that variability is inherent in all animals and plants.
Analyzing the material on the variability of animals, the scientist noticed that any change in living conditions is enough to cause variability. Thus, Darwin understood variability as the ability of organisms to acquire new characteristics under the influence of environmental conditions. He distinguished the following forms of variability:
Specific (group) variability(now called modification) - a similar change in all individuals of the offspring in one direction due to the influence of certain conditions. Certain changes tend to be non-hereditary.
Uncertain individual variability(now called genotypic) - the appearance of various minor differences in individuals of the same species, variety, breed, by which, existing in similar conditions, one individual differs from others. Such multidirectional variability is a consequence of the uncertain influence of living conditions on each individual.
Correlative(or relative) variability. Darwin understood the organism as an integral system, the individual parts of which are closely interconnected. Therefore, a change in the structure or function of one part often causes a change in another or others. An example of such variability is the relationship between the development of a functioning muscle and the formation of the ridge on the bone to which it is attached. Many wading birds have a correlation between neck length and limb length: birds with long necks also have long limbs.
Compensatory variability consists in the fact that the development of some organs or functions is often the cause of the inhibition of others, that is, there is an inverse correlation, for example, between milk production and meatiness of livestock.

89. Modification variability. Norm of reaction of genetically determined traits. Phenocopies.
Phenotypic variability covers changes in the state of the characteristics themselves that occur under the influence of developmental conditions or environmental factors. The range of modification variability is limited by the reaction norm. A specific modification change in a trait that has arisen is not inherited, but the range of modification variability is determined by heredity. Hereditary material is not involved in the change.
Norm of reaction is the limit of modification variability of a trait. It is the reaction norm that is inherited, not the modifications themselves, i.e. the ability to develop a trait, and the form of its manifestation depends on environmental conditions. The reaction norm is a specific quantitative and qualitative characteristic of the genotype. There are signs with a wide reaction norm, a narrow () and an unambiguous norm. Norm of reaction has limits or boundaries for each biological species (lower and upper) - for example, increased feeding will lead to an increase in the weight of the animal, but it will be within the normal reaction range characteristic of a given species or breed. The reaction rate is genetically determined and inherited. For different traits, the reaction norm limits vary greatly. For example, wide limits of the reaction norm are the value of milk yield, cereal productivity and many other quantitative characteristics, narrow limits are the color intensity of most animals and many other qualitative characteristics. Under the influence of some harmful factors that a person does not encounter in the process of evolution, the possibility of modification variability that determines reaction norms is excluded.
Phenocopies- changes in phenotype under the influence of unfavorable environmental factors, similar in manifestation to mutations. The resulting phenotypic modifications are not inherited. It has been established that the occurrence of phenocopies is associated with the influence of external conditions on a certain limited stage of development. Moreover, the same agent, depending on which phase it acts on, can copy different mutations, or one stage reacts to one agent, another to another. Different agents can be used to induce the same phenocopy, indicating that there is no connection between the result of the change and the influencing factor. The most complex genetic developmental disorders are relatively easy to reproduce, while copying traits is much more difficult.

90. Adaptive nature of modification. The role of heredity and environment in human development, training and education.
Modification variability corresponds to living conditions and is adaptive in nature. Characteristics such as the growth of plants and animals, their weight, color, etc. are subject to modification variability. The occurrence of modification changes is due to the fact that environmental conditions affect the enzymatic reactions occurring in the developing organism and, to a certain extent, change its course.
Since the phenotypic manifestation of hereditary information can be modified by environmental conditions, the organism’s genotype is programmed only with the possibility of their formation within certain limits, called the reaction norm. The reaction norm represents the limits of modification variability of a trait allowed for a given genotype.
The degree of expression of a trait when a genotype is realized under different conditions is called expressivity. It is associated with the variability of the trait within the reaction norm.
The same trait may appear in some organisms and be absent in others that have the same gene. A quantitative measure of the phenotypic expression of a gene is called penetrance.
Expressivity and penetrance are maintained by natural selection. Both patterns must be kept in mind when studying heredity in humans. By changing environmental conditions, penetrance and expressivity can be influenced. The fact that the same genotype can be the source of the development of different phenotypes is of significant importance for medicine. This means that the burden does not necessarily have to manifest itself. Much depends on the conditions in which a person finds himself. In some cases, diseases as a phenotypic manifestation of hereditary information can be prevented by following a diet or taking medications. The implementation of hereditary information depends on the environment. Formed on the basis of a historically established genotype, modifications are usually adaptive in nature, since they are always the result of responses of a developing organism to environmental factors affecting it. The nature of mutational changes is different: they are the result of changes in the structure of the DNA molecule, which causes a disruption in the previously established process of protein synthesis. When mice are kept at elevated temperatures, they produce offspring with elongated tails and enlarged ears. This modification is adaptive in nature, since the protruding parts (tail and ears) play a thermoregulatory role in the body: increasing their surface allows for increased heat transfer.

The genetic potential of a person is limited in time, and quite strictly. If you miss the deadline for early socialization, it will fade away before it has time to be realized. A striking example of this statement are the numerous cases when infants, by force of circumstances, ended up in the jungle and spent several years among animals. After their return to the human community, they could no longer fully catch up with what they had lost: master speech, acquire quite complex skills of human activity, their mental functions of a person developed poorly. This is evidence that the characteristic features of human behavior and activity are acquired only through social inheritance, only through the transmission of a social program in the process of upbringing and training.

Identical genotypes (in identical twins), when placed in different environments, can produce different phenotypes. Taking into account all the influencing factors, the human phenotype can be represented as consisting of several elements.

These include: biological inclinations encoded in genes; environment (social and natural); individual activity; mind (consciousness, thinking).

The interaction of heredity and environment in human development plays an important role throughout his life. But it acquires particular importance during the periods of formation of the body: embryonic, breast, childhood, adolescence and youth. It is at this time that an intensive process of development of the body and formation of personality is observed.

Heredity determines what an organism can become, but a person develops under the simultaneous influence of both factors - heredity and environment. Today it is becoming generally accepted that human adaptation is carried out under the influence of two programs of heredity: biological and social. All signs and properties of any individual are the result of the interaction of his genotype and environment. Therefore, each person is both a part of nature and a product of social development.

91. Combinative variability. The importance of combinative variability in ensuring the genotypic diversity of people: Marriage systems. Medical and genetic aspects of the family.
Combinative variability associated with obtaining new combinations of genes in the genotype. This is achieved as a result of three processes: a) independent chromosome segregation during meiosis; b) their random combination during fertilization; c) gene recombination due to Crossing Over. The hereditary factors (genes) themselves do not change, but their new combinations arise, which leads to the appearance of organisms with different genotypic and phenotypic properties. Thanks to combinative variability a variety of genotypes is created in the offspring, which is of great importance for the evolutionary process due to the fact that: 1) the diversity of material for the evolutionary process increases without reducing the viability of individuals; 2) the ability of organisms to adapt to changing environmental conditions expands and thereby ensures the survival of a group of organisms (population, species) as a whole

The composition and frequency of alleles in people and populations largely depend on the types of marriages. In this regard, the study of types of marriages and their medical and genetic consequences is important.

Marriages can be: selective, indiscriminate.

To the non-selective include panmix marriages. Panmixia(Greek nixis - mixture) - step marriages between people with different genotypes.

Selective marriages: 1.Outbreeding– marriages between people who are not related by a previously known genotype, 2.Inbreeding- marriages between relatives, 3.Positively assortative– marriages between individuals with similar phenotypes (deaf-mute, short with short, tall with tall, feeble-minded with feeble-minded, etc.). 4.Negative assortative-marriages between people with dissimilar phenotypes (deaf-mute - normal; short - tall; normal - with freckles, etc.). 4.Incest– marriages between close relatives (between brother and sister).

Inbred and incestuous marriages are illegal in many countries. Unfortunately, there are regions with a high frequency of inbred marriages. Until recently, the frequency of inbred marriages in some regions of Central Asia reached 13-15%.

Medical and genetic significance inbred marriages are very negative. In such marriages, homozygotization is observed, and the frequency of autosomal recessive diseases increases by 1.5-2 times. Inbred populations experience inbreeding depression, i.e. the frequency of unfavorable recessive alleles increases sharply, and child mortality increases. Positively assortative marriages also lead to similar phenomena. Outbreeding has positive genetic benefits. In such marriages, heterozygotization is observed.

92. Mutational variability, classification of mutations according to the level of change in the damage to the hereditary material. Mutations in germ and somatic cells.
Mutation called a change caused by the reorganization of reproductive structures, a change in its genetic apparatus. Mutations occur spasmodically and are inherited. Depending on the level of change in the hereditary material, all mutations are divided into genetic, chromosomal And genomic.
Gene mutations, or transgenations, affect the structure of the gene itself. Mutations can change sections of the DNA molecule of varying lengths. The smallest region, the change of which leads to the appearance of a mutation, is called a muton. It can only be made up of a pair of nucleotides. A change in the sequence of nucleotides in DNA causes a change in the sequence of triplets and, ultimately, the protein synthesis program. It should be remembered that disturbances in the DNA structure lead to mutations only when repair is not carried out.
Chromosomal mutations, chromosomal rearrangements or aberrations consist of a change in the amount or redistribution of the hereditary material of chromosomes.
Perestroikas are divided into intrachromosomal And interchromosomal. Intrachromosomal rearrangements consist of the loss of part of a chromosome (deletion), doubling or multiplication of some of its sections (duplication), and rotation of a chromosome fragment by 180° with a change in the sequence of gene location (inversion).
Genomic mutations associated with changes in the number of chromosomes. Genomic mutations include aneuploidy, haploidy and polyploidy.
Aneuploidy called a change in the number of individual chromosomes - the absence (monosomy) or the presence of additional (trisomy, tetrasomy, generally polysomy) chromosomes, i.e. an unbalanced chromosome set. Cells with an altered number of chromosomes appear as a result of disturbances in the process of mitosis or meiosis, and therefore a distinction is made between mitotic and meiotic aneuploidy. A multiple decrease in the number of chromosome sets of somatic cells compared to diploid is called haploidy. A multiple increase in the number of chromosome sets of somatic cells compared to diploid is called polyploidy.
The listed types of mutations occur in both germ cells and somatic cells. Mutations that occur in germ cells are called generative. They are passed on to subsequent generations.
Mutations that occur in bodily cells at one or another stage of the individual development of the organism are called somatic. Such mutations are inherited only by the descendants of the cell in which it occurred.

93. Gene mutations, molecular mechanisms of occurrence, frequency of mutations in nature. Biological antimutation mechanisms.
Modern genetics emphasizes that gene mutations consist in changing the chemical structure of genes. Specifically, gene mutations are substitutions, insertions, deletions, and losses of nucleotide pairs. The smallest section of a DNA molecule whose change leads to mutation is called a muton. It is equal to one pair of nucleotides.
There are several classifications of gene mutations . Spontaneous(spontaneous) is a mutation that occurs without direct connection with any physical or chemical environmental factor.
If mutations are caused intentionally, by influencing the body by factors of a known nature, they are called induced. The agent that induces mutations is called mutagen.
The nature of mutagens is diverse- these are physical factors, chemical compounds. The mutagenic effect of some biological objects - viruses, protozoa, helminths - when they penetrate the human body has been established.
As a result of dominant and recessive mutations, dominant and recessive altered traits appear in the phenotype. Dominant mutations appear in the phenotype already in the first generation. Recessive mutations are hidden in heterozygotes from the action of natural selection, so they accumulate in large numbers in the gene pools of species.
An indicator of the intensity of the mutation process is the mutation frequency, which is calculated on average per genome or separately for specific loci. The average mutation frequency is comparable in a wide range of living beings (from bacteria to humans) and does not depend on the level and type of morphophysiological organization. It is equal to 10 -4 - 10 -6 mutations per 1 locus per generation.
Antimutation mechanisms.
A protective factor against the adverse consequences of gene mutations is the pairing of chromosomes in the diploid karyotype of somatic eukaryotic cells. The pairing of alley genes prevents the phenotypic manifestation of mutations if they are recessive.
The phenomenon of extracopying genes encoding vital macromolecules contributes to reducing the harmful consequences of gene mutations. For example, the genes of rRNA, tRNA, histone proteins, without which the life of any cell is impossible.
The listed mechanisms contribute to the preservation of genes selected during evolution and at the same time the accumulation of different alleles in the gene pool of a population, forming a reserve of hereditary variability.

94. Genomic mutations: polyploidy, haploidy, heteroploidy. Mechanisms of their occurrence.
Genomic mutations are associated with changes in the number of chromosomes. Genomic mutations include heteroploidy, haploidy And polyploidy.
Polyploidy– an increase in the diploid number of chromosomes by adding entire chromosome sets as a result of disruption of meiosis.
In polyploid forms, there is an increase in the number of chromosomes, a multiple of the haploid set: 3n – triploid; 4n – tetraploid, 5n – pentaploid, etc.
Polyploid forms are phenotypically different from diploid ones: along with a change in the number of chromosomes, hereditary properties also change. In polyploids, the cells are usually large; sometimes the plants are gigantic in size.
Forms resulting from the multiplication of chromosomes of one genome are called autoploid. However, another form of polyploidy is also known - alloploidy, in which the number of chromosomes of two different genomes is multiplied.
A multiple decrease in the number of chromosome sets of somatic cells compared to diploid is called haploidy. Haploid organisms in natural habitats are found mainly among plants, including higher ones (datura, wheat, corn). The cells of such organisms have one chromosome of each homologous pair, so all recessive alleles are manifested in the phenotype. This explains the reduced viability of haploids.
Heteroploidy. As a result of disturbances in mitosis and meiosis, the number of chromosomes may change and not become a multiple of the haploid set. The phenomenon when one of the chromosomes, instead of being a pair, ends up in a triple number, is called trisomy. If trisomy is observed on one chromosome, then such an organism is called trisomic and its chromosome set is 2n+1. Trisomy can be on any of the chromosomes or even on several. With Double trisomy, it has a chromosome set of 2n+2, triple trisomy – 2n+3, etc.
The opposite phenomenon trisomy, i.e. the loss of one chromosome from a pair in a diploid set is called monosomy, the organism is monosomic; its genotypic formula is 2n-1. In the absence of two different chromosomes, the organism is double monosomic with the genotypic formula 2n-2, etc.
From what has been said it is clear that aneuploidy, i.e. a violation of the normal number of chromosomes leads to changes in the structure and a decrease in the viability of the organism. The greater the disturbance, the lower the viability. In humans, disruption of a balanced set of chromosomes leads to painful conditions known collectively as chromosomal diseases.
Mechanism of occurrence genomic mutations are associated with the pathology of disruption of normal chromosome segregation in meiosis, resulting in the formation of abnormal gametes, which leads to mutation. Changes in the body are associated with the presence of genetically heterogeneous cells.

95. Methods for studying human heredity. Genealogical and twin methods, their significance for medicine.
The main methods for studying human heredity are genealogical, twin, population-statistical, dermatoglyphics method, cytogenetic, biochemical, somatic cell genetics method, modeling method
Genealogical method. This method is based on the compilation and analysis of pedigrees. A pedigree is a diagram that shows the connections between family members. By analyzing pedigrees, they study any normal or (more often) pathological trait in generations of people who are related.
Genealogical methods are used to determine the hereditary or non-hereditary nature of a trait, dominance or recessivity, chromosome mapping, sex linkage, and to study the mutation process. As a rule, the genealogical method forms the basis for conclusions in medical genetic counseling.
When compiling pedigrees, standard notations are used. The person with whom the study begins is the proband. The descendant of a married couple is called a sibling, siblings are called siblings, cousins ​​are called first cousins, etc. Descendants who have a common mother (but different fathers) are called consanguineous, and descendants who have a common father (but different mothers) are called half-blooded; if a family has children from different marriages, and they do not have common ancestors (for example, a child from the mother’s first marriage and a child from the father’s first marriage), then they are called step-children.
Using the genealogical method, the hereditary nature of the trait being studied can be established, as well as the type of its inheritance. When analyzing pedigrees for several characteristics, the linked nature of their inheritance can be revealed, which is used in the compilation of chromosomal maps. This method allows you to study the intensity of the mutation process, assess the expressivity and penetrance of the allele.
Twin method. It consists of studying the patterns of inheritance of traits in pairs of identical and fraternal twins. Twins are two or more children conceived and born by the same mother almost simultaneously. There are identical and fraternal twins.
Identical (monozygotic, identical) twins occur at the earliest stages of zygote fragmentation, when two or four blastomeres retain the ability to develop into a full-fledged organism when separated. Because the zygote divides by mitosis, the genotypes of identical twins are, at least initially, completely identical. Identical twins are always the same sex and share the same placenta during fetal development.
Fraternal (dizygotic, non-identical) occur when two or more simultaneously matured eggs are fertilized. Thus, they share about 50% of their genes. In other words, they are similar to ordinary brothers and sisters in their genetic constitution and can be either same-sex or opposite-sex.
By comparing identical and fraternal twins raised in the same environment, conclusions can be drawn about the role of genes in the development of traits.
The twin method allows you to make informed conclusions about the heritability of traits: the role of heredity, environment and random factors in determining certain human traits
Prevention and diagnosis of hereditary pathology
Currently, the prevention of hereditary pathology is carried out at four levels: 1) pregametic; 2) prezygotic; 3) prenatal; 4) neonatal.
1.) Pregametic level
Carried out:
1. Sanitary control over production - eliminating the influence of mutagens on the body.
2. Liberation of women of childbearing age from work in hazardous industries.
3.Creation of lists of hereditary diseases that are common in a certain area
territories with def. frequent.
2.Prezygotic level
The most important element of this level of prevention is medical genetic counseling (MGC) of the population, informing the family about the degree of possible risk of having a child with a hereditary pathology and providing assistance in making the right decision about childbearing.
Prenatal level
It consists of carrying out prenatal (prenatal) diagnostics.
Prenatal diagnosis– this is a set of measures that is carried out with the aim of determining hereditary pathology in the fetus and terminating this pregnancy. Prenatal diagnostic methods include:
1. Ultrasound scanning (USS).
2. Fetoscopy– a method of visual observation of the fetus in the uterine cavity through an elastic probe equipped with an optical system.
3. Chorionic villus biopsy. The method is based on taking chorionic villi, culturing cells and studying them using cytogenetic, biochemical and molecular genetic methods.
4. Amniocentesis– puncture of the amniotic sac through the abdominal wall and collection
amniotic fluid. It contains fetal cells that can be examined
cytogenetically or biochemically, depending on the expected pathology of the fetus.
5. Cordocentesis- puncture of the umbilical cord vessels and collection of fetal blood. Fetal lymphocytes
cultivated and subjected to research.
4.Neonatal level
At the fourth level, newborns are screened to identify autosomal recessive metabolic diseases in the preclinical stage, when timely treatment begins to ensure normal mental and physical development of children.

Principles of treatment of hereditary diseases
The following types of treatment are available:.
1. Symptomatic(impact on disease symptoms).
2. Pathogenetic(impact on the mechanisms of disease development).
Symptomatic and pathogenetic treatment does not eliminate the causes of the disease, because does not liquidate
genetic defect.
The following techniques can be used in symptomatic and pathogenetic treatment.
· Correction developmental defects using surgical methods (syndactyly, polydactyly,
cleft lip...
· Replacement therapy, the meaning of which is to introduce into the body
missing or insufficient biochemical substrates.
· Metabolism induction– introduction into the body of substances that enhance synthesis
some enzymes and, therefore, speed up processes.
· Metabolism inhibition– introduction into the body of drugs that bind and remove
abnormal metabolic products.
· Diet therapy ( therapeutic nutrition) - elimination from the diet of substances that
cannot be absorbed by the body.
Prospects: In the near future, genetics will develop rapidly, although it is still
very widespread in agricultural crops (breeding, cloning),
medicine (medical genetics, genetics of microorganisms). In the future, scientists hope
use genetics to eliminate defective genes and eradicate diseases transmitted
by inheritance, to be able to treat such serious diseases as cancer, viral
infections.

With all the shortcomings of the modern assessment of the radiogenetic effect, there is no doubt about the seriousness of the genetic consequences awaiting humanity in the event of an uncontrolled increase in the radioactive background in the environment. The danger of further testing of atomic and hydrogen weapons is obvious.
At the same time, the use of atomic energy in genetics and selection makes it possible to create new methods for controlling the heredity of plants, animals and microorganisms, and to better understand the processes of genetic adaptation of organisms. In connection with human flights into outer space, there is a need to study the influence of the cosmic reaction on living organisms.

98. Cytogenetic method for diagnosing human chromosomal disorders. Amniocentesis. Karyotype and idiogram of human chromosomes. Biochemical method.
The cytogenetic method involves studying chromosomes using a microscope. Most often, the object of study is mitotic (metaphase), less often meiotic (prophase and metaphase) chromosomes. Cytogenetic methods are used to study the karyotypes of individual individuals
Obtaining material from an organism developing in utero is carried out in different ways. One of them is amniocentesis, with the help of which, at 15-16 weeks of pregnancy, amniotic fluid is obtained, containing waste products of the fetus and cells of its skin and mucous membranes
The material taken during amniocentesis is used for biochemical, cytogenetic and molecular chemical studies. Cytogenetic methods determine the sex of the fetus and identify chromosomal and genomic mutations. The study of amniotic fluid and fetal cells using biochemical methods makes it possible to detect a defect in the protein products of genes, but does not make it possible to determine the localization of mutations in the structural or regulatory part of the genome. The use of DNA probes plays an important role in identifying hereditary diseases and precise localization of damage to the fetal hereditary material.
Currently, amniocentesis is used to diagnose all chromosomal abnormalities, over 60 hereditary metabolic diseases, and incompatibility of mother and fetus with erythrocyte antigens.
The diploid set of chromosomes of a cell, characterized by their number, size and shape, is called karyotype. A normal human karyotype includes 46 chromosomes, or 23 pairs: 22 pairs of autosomes and one pair of sex chromosomes
In order to make it easier to understand the complex complex of chromosomes that makes up the karyotype, they are arranged in the form idiograms. IN idiogram chromosomes are arranged in pairs in order of decreasing size, with the exception of sex chromosomes. The largest pair is assigned No. 1, the smallest - No. 22. Identification of chromosomes only by size encounters great difficulties: a number of chromosomes have similar sizes. However, recently, through the use of various types of dyes, a clear differentiation of human chromosomes according to their length into bands that can be dyed using special methods and those that cannot be dyed has been established. The ability to accurately differentiate chromosomes is of great importance for medical genetics, as it allows one to accurately determine the nature of abnormalities in a person’s karyotype.
Biochemical method

99. Human karyotype and idiogram. Characteristics of a normal human karyotype
and pathology.
Karyotype- a set of characteristics (number, size, shape, etc.) of the complete set of chromosomes,
inherent in the cells of a given biological species (species karyotype), of a given organism
(individual karyotype) or line (clone) of cells.
To determine the karyotype, a microphotograph or sketch of chromosomes is used during microscopy of dividing cells.
Each person has 46 chromosomes, two of which are sex chromosomes. A woman has two X chromosomes
(karyotype: 46, XX), and men have one X chromosome and the other Y (karyotype: 46, XY). Study
Karyotyping is carried out using a method called cytogenetics.
Idiogram- a schematic representation of the haploid set of chromosomes of an organism, which
placed in a row in accordance with their sizes, in pairs in descending order of their sizes. An exception is made for sex chromosomes, which are especially distinguished.
Examples of the most common chromosomal pathologies.
Down syndrome is a trisomy of the 21st pair of chromosomes.
Edwards syndrome is trisomy on the 18th pair of chromosomes.
Patau syndrome is a trisomy of the 13th pair of chromosomes.
Klinefelter syndrome is a polysomy of the X chromosome in boys.

100. The importance of genetics for medicine. Cytogenetic, biochemical, population-statistical methods for studying human heredity.
The role of genetics in human life is very important. It is implemented with the help of medical genetic counseling. Medical genetic counseling is designed to save humanity from suffering associated with hereditary (genetic) diseases. The main goals of medical genetic counseling are to establish the role of the genotype in the development of this disease and predict the risk of having sick offspring. Recommendations given in medical genetic consultations regarding marriage or prognosis of the genetic usefulness of offspring are aimed at ensuring that they are taken into account by the persons being consulted, who voluntarily make the appropriate decision.
Cytogenetic (karyotypic) method. The cytogenetic method involves studying chromosomes using a microscope. Most often, the object of study is mitotic (metaphase), less often meiotic (prophase and metaphase) chromosomes. This method is also used to study sex chromatin ( Barr bodies) Cytogenetic methods are used to study the karyotypes of individual individuals
The use of the cytogenetic method allows not only to study the normal morphology of chromosomes and the karyotype as a whole, to determine the genetic sex of the organism, but, most importantly, to diagnose various chromosomal diseases associated with changes in the number of chromosomes or disruption of their structure. In addition, this method allows you to study mutagenesis processes at the chromosome and karyotype levels. Its use in medical genetic counseling for the purposes of prenatal diagnosis of chromosomal diseases makes it possible, through timely termination of pregnancy, to prevent the appearance of offspring with severe developmental disorders.
Biochemical method consists of determining the activity of enzymes or the content of certain metabolic products in the blood or urine. Using this method, metabolic disorders caused by the presence in the genotype of an unfavorable combination of allelic genes, most often recessive alleles in a homozygous state, are identified. With timely diagnosis of such hereditary diseases, preventive measures make it possible to avoid serious developmental disorders.
Population statistical method. This method allows you to estimate the probability of birth of individuals with a certain phenotype in a given population group or in consanguineous marriages; calculate the frequency of carriage in the heterozygous state of recessive alleles. The method is based on the Hardy-Weinberg law. Hardy-Weinberg Law- This is the law of population genetics. The law states: “In an ideal population, the frequencies of genes and genotypes remain constant from generation to generation.”
The main features of human populations are: common territory and the possibility of free marriage. Factors of isolation, i.e. restriction of a person’s freedom of choice of spouses, can be not only geographical, but also religious and social barriers.
In addition, this method makes it possible to study the mutation process, the role of heredity and environment in the formation of human phenotypic polymorphism according to normal characteristics, as well as in the occurrence of diseases, especially with a hereditary predisposition. The population statistical method is used to determine the significance of genetic factors in anthropogenesis, in particular in race formation.

101.Structural disorders (aberrations) of chromosomes. Classification depending on changes in genetic material. Implications for biology and medicine.
Chromosomal aberrations result from chromosome rearrangements. They are a consequence of a chromosome break, leading to the formation of fragments that are subsequently reunited, but the normal structure of the chromosome is not restored. There are 4 main types of chromosomal aberrations: shortage, doublings, inversions, translocations, deletion- loss of a specific chromosome region, which is then usually destroyed
Shortages arise due to the loss of a chromosome of one or another region. Deficiencies in the middle part of the chromosome are called deletions. The loss of a significant part of a chromosome leads to death of the organism, the loss of minor sections causes a change in hereditary properties. So. When corn is missing one of its chromosomes, its seedlings lack chlorophyll.
Doubling associated with the inclusion of an extra, duplicating section of the chromosome. This also leads to the appearance of new symptoms. Thus, in Drosophila, the gene for stripe-shaped eyes is caused by the doubling of a section of one of the chromosomes.
Inversions observed when a chromosome breaks and the torn section is turned 180 degrees. If the break occurs in one place, the detached fragment is attached to the chromosome with the opposite end, but if in two places, then the middle fragment, turning over, is attached to the places of the break, but with different ends. According to Darwin, inversions play an important role in the evolution of species.
Translocations arise in cases when a section of a chromosome from one pair is attached to a non-homologous chromosome, i.e. chromosome from another pair. Translocation sections of one of the chromosomes are known in humans; it may be the cause of Down's syndrome. Most translocations affecting large sections of chromosomes render the organism nonviable.
Chromosomal mutations change the dose of some genes, cause redistribution of genes between linkage groups, change their localization in the linkage group. By doing this, they disrupt the gene balance of the body's cells, resulting in deviations in the somatic development of the individual. As a rule, changes extend to several organ systems.
Chromosomal aberrations are of great importance in medicine. At chromosomal aberrations, there is a delay in general physical and mental development. Chromosomal diseases are characterized by a combination of many congenital defects. This defect is a manifestation of Down syndrome, which is observed in the case of trisomy on a small segment of the long arm of chromosome 21. The picture of cat cry syndrome develops with the loss of a section of the short arm of chromosome 5. In humans, malformations of the brain, musculoskeletal, cardiovascular, and genitourinary systems are most often observed.

102. The concept of species, modern views on speciation. Type criteria.
View is a collection of individuals that are similar in terms of species criteria to such an extent that they can
naturally interbreed and produce fertile offspring.
Fertile offspring- something that can reproduce itself. An example of infertile offspring is a mule (a hybrid of a donkey and a horse), it is infertile.
Type criteria- these are characteristics by which 2 organisms are compared to determine whether they belong to the same species or to different ones.
· Morphological – internal and external structure.
· Physiological-biochemical – how organs and cells work.
· Behavioral – behavior, especially at the time of reproduction.
· Ecological – a set of environmental factors necessary for life
type (temperature, humidity, food, competitors, etc.)
· Geographical – area (area of ​​distribution), i.e. the territory in which the species lives.
· Genetic-reproductive – the same number and structure of chromosomes, which allows organisms to produce fertile offspring.
Type criteria are relative, i.e. A species cannot be judged by one criterion. For example, there are twin species (in the malaria mosquito, in rats, etc.). They do not differ morphologically from each other, but have a different number of chromosomes and therefore do not produce offspring.

103.Population. Its ecological and genetic characteristics and role in speciation.
Population- a minimal self-reproducing group of individuals of the same species, more or less isolated from other similar groups, inhabiting a certain area for a long series of generations, forming its own genetic system and forming its own ecological niche.
Ecological indicators of the population.
Number- the total number of individuals in the population. This value is characterized by a wide range of variability, but it cannot be below certain limits.
Density- the number of individuals per unit area or volume. As numbers increase, population density tends to increase
Spatial structure A population is characterized by the peculiarities of the distribution of individuals in the occupied territory. It is determined by the properties of the habitat and the biological characteristics of the species.
Sexual structure reflects a certain ratio of male and female individuals in the population.
Age structure reflects the ratio of different age groups in populations, depending on life expectancy, time of puberty, and the number of descendants.
Genetic indicators of the population. Genetically, a population is characterized by its gene pool. It is represented by a set of alleles that form the genotypes of organisms in a given population.
When describing populations or comparing them with each other, a number of genetic characteristics are used. Polymorphism. A population is called polymorphic at a given locus if two or more alleles occur in it. If a locus is represented by a single allele, we speak of monomorphism. By examining many loci, it is possible to determine the proportion of polymorphic ones among them, i.e. assess the degree of polymorphism, which is an indicator of the genetic diversity of the population.
Heterozygosity. An important genetic characteristic of a population is heterozygosity - the frequency of heterozygous individuals in the population. It also reflects genetic diversity.
Coefficient of inbreeding. This coefficient is used to estimate the prevalence of inbreeding in a population.
Gene association. Allele frequencies of different genes can depend on each other, which is characterized by association coefficients.
Genetic distances. Different populations differ from each other in allele frequencies. To quantify these differences, metrics called genetic distances have been proposed.

Population– elementary evolutionary structure. In the range of any species, individuals are distributed unevenly. Areas of dense concentration of individuals alternate with spaces where there are few or none of them. As a result, more or less isolated populations arise in which random free interbreeding (panmixia) systematically occurs. Interbreeding with other populations occurs very rarely and irregularly. Thanks to panmixia, a characteristic gene pool is created in each population, different from other populations. It is the population that should be recognized as the elementary unit of the evolutionary process

The role of populations is great, since almost all mutations occur within it. These mutations are primarily associated with isolated populations and gene pools that differ due to their isolation from each other. The material for evolution is mutational variability, which begins in a population and ends with the formation of a species.

All morphological, anatomical and functional features of any living cell and organism as a whole are determined by the structure of specific proteins that make up the cells. The ability to synthesize only strictly defined proteins is a hereditary property of organisms. The sequence of amino acids in the polypeptide chain - the primary structure of the protein, on which its biological properties depend - is determined by the sequence of nucleotides in DNA molecules. The latter is the keeper of hereditary information in cells.

The sequence of nucleotides in the polynucleotide chain of DNA is very specific for each cell and represents genetic code, through which information about the synthesis of certain proteins is recorded. This means that in DNA, each message is encoded with a specific sequence of four characters - A, G, T, C, just as a written message is encoded with characters (letters) of the alphabet or Morse code. The genetic code is triplet, i.e., each amino acid is encoded by a known combination of three adjacent nucleotides, called codon. It is easy to calculate that the number of possible combinations of four nucleotides in threes will be 64.

It turned out that the code is multiple or “degenerate”, i.e. the same amino acid can be encoded by several triplet codons (from 2 to b), while each triplet encodes only one amino acid, for example, in the language of messenger RNA:

• phenylalanine - UUU, UUC;
• isoleucine - AUC, AUC, AUA;
• proline - CCU, CCC, CCA, CCG;
• serine - UCU, UCC, UCA, UCG, AGU, AGC.

Apart from this, the code is non-overlapping, t.s. the same nucleotide cannot simultaneously be part of two neighboring triplets. And finally, this code does not have commas, which means that if one nucleotide is missing, then when reading it, the nearest nucleotide from the neighboring codon will take its place, which will change the entire reading order. Therefore, correct reading of the code from messenger RNA is ensured by telco if it is read from a strictly defined point. The starting codons in the molecule and RNA are the triplets AUG and GU G.

The nucleotide code is universal for all living organisms and viruses: identical triplets code for identical amino acids. This discovery represents a serious step towards a deeper understanding of the essence of living matter, because the universality of the genetic code indicates the unity of origin of all living organisms. To date, triplets have been deciphered for all 20 amino acids that make up natural proteins. Therefore, knowing the order of triplets in a DNA molecule (genetic code), it is possible to establish the order of amino acids in a protein.

A single DNA molecule can encode the amino acid sequence for many proteins. A functional segment of a DNA molecule that carries information about the structure of one polypeptide or RNA molecule is called genome. There are structural genes, which encode information for the synthesis of structural and enzymatic proteins, and genes with information for the synthesis of tRNA, rRNA, etc.

Each protein is a chain or several chains of amino acids in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties. The set of amino acids is also universal for almost all living organisms.

C

CUU (Leu/L)Leucine
CUC (Leu/L)Leucine
CUA (Leu/L)Leucine
CUG (Leu/L)Leucine

In some proteins, nonstandard amino acids such as selenocysteine ​​and pyrrolysine are inserted by the ribosome reading the stop codon, which depends on the sequences in the mRNA. Selenocysteine ​​is now considered to be the 21st, and pyrrolysine the 22nd, amino acids that make up proteins.

Despite these exceptions, all living organisms have common genetic codes: a codon consists of three nucleotides, where the first two are decisive; codons are translated by tRNA and ribosomes into an amino acid sequence.

Deviations from the standard genetic code.

Example	Codon	Normal meaning	Reads like:
Some types of yeast Candida	C.U.G.	Leucine	Serin
Mitochondria, in particular in Saccharomyces cerevisiae	CU(U, C, A, G)	Leucine	Serin
Mitochondria of higher plants	CGG	Arginine	Tryptophan
Mitochondria (in all studied organisms without exception)	U.G.A.	Stop	Tryptophan
Mitochondria in mammals, Drosophila, S. cerevisiae and many protozoa	AUA	Isoleucine	Methionine = Start
Bacteria	G.U.G.	Valin	Start
Eukaryotes (rare)	C.U.G.	Leucine	Start
Eukaryotes (rare)	G.U.G.	Valin	Start
Bacteria	G.U.G.	Valin	Start
Bacteria (rare)	UUG	Leucine	Start
Eukaryotes (rare)	A.C.G.	Threonine	Start
Mammalian mitochondria	AGC, AGU	Serin	Stop
Drosophila mitochondria	A.G.A.	Arginine	Stop
Mammalian mitochondria	AG(A, G)	Arginine	Stop

Notes

Literature

• Azimov A. Genetic code. From the theory of evolution to deciphering DNA. - M.: Tsentrpoligraf, 2006. - 208 pp. - ISBN 5-9524-2230-6.
• Ratner V. A. Genetic code as a system - Soros educational journal, 2000, 6, No. 3, pp. 17-22.

Links

• Genetic code - article by N. P. Dubinin and V. N. Soifer in the Great Soviet Encyclopedia
• Genetic code in the Chemical Encyclopedia on the website
• Genetic code in the Dictionary of Natural Sciences "Glossary.ru"

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See what “Genetic code” is in other dictionaries:

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English code, genetic; German Kod, genetischer. A system for recording hereditary information in DNA molecules of living organisms. Antinazi. Encyclopedia of Sociology, 2009 ... Encyclopedia of Sociology

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A system for “recording” hereditary information in nucleic acid molecules; see Genetic code... Great Soviet Encyclopedia

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genetic code- A natural code for recording and storing genetic information in nucleic acid molecules in the form of a specific linear sequence of nucleotides... Dictionary of linguistic terms T.V. Foal

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CODE GENETIC- English code, genetic; German Kod, genetischer. A system for recording hereditary information in DNA molecules of living organisms... Explanatory dictionary of sociology

Genetic code- Information contained in nucleic acid molecules in the form of a sequence of nucleotides about the hereditary qualities characteristic of a given type of living organism... Adaptive physical culture. Concise encyclopedic dictionary