genetic move. Biosynthesis of protein and nucleic acids

GENETIC CODE, a method of recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides forming these acids. 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 that is part of its molecule begins: A (A) - adenine, G (G) - guanine, C (C) - cytosine, T (T) - thymine; in RNA, instead of thymine, uracil is U (U). Each is encoded by a combination of three nucleotides - a triplet, or codon. Briefly, the way of transferring genetic information is summarized in the so-called. the central dogma of molecular biology: DNA ` RNA f protein.

In special cases, information can be transferred from RNA to DNA, but never from protein to genes.

Realization of genetic information is carried out in two stages. In the cell nucleus, information, or matrix, RNA (transcription) is synthesized on DNA. In this case, the nucleotide sequence of DNA is "rewritten" (recoded) into the nucleotide sequence of mRNA. Then mRNA passes into the cytoplasm, attaches to the ribosome, and on it, as on a matrix, a polypeptide protein chain is synthesized (translation). Amino acids with the help of transfer RNA are attached to the chain under construction in a sequence determined by the order of nucleotides in mRNA.

From the four "letters" you can make 64 different three-letter "words" (codons). Of the 64 codons, 61 encode certain amino acids, and three are responsible for the completion of the synthesis of the polypeptide chain. Since there are 61 codons for 20 amino acids that make up proteins, some amino acids are encoded by more than one codon (the so-called code degeneracy). Such redundancy increases the reliability of the code and the entire mechanism of protein biosynthesis. Another property of the code is its specificity (unambiguity): one codon encodes only one amino acid.

In addition, the code does not overlap - the information is read in one direction sequentially, triplet by triplet. The most amazing property of the code is its universality: it is the same for all living beings - from bacteria to humans (with the exception of the genetic code of mitochondria). Scientists see this as confirmation of the concept of the origin of all organisms from one common ancestor.

The decoding of the genetic code, i.e., the determination of the "meaning" of each codon and the rules by which information is read, was carried out in 1961–1965. and is considered one of the most striking achievements of molecular biology.

They line up in chains and, thus, sequences of genetic letters are obtained.

Genetic code

The proteins of almost all living organisms are built from only 20 types of amino acids. These amino acids are called canonical. Each protein is a chain or several chains of amino acids connected in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties.

C

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

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

Despite these exceptions, the genetic code of all living organisms has common features: a codon consists of three nucleotides, where the first two are defining, codons are translated by tRNA and ribosomes into a sequence of amino acids.

Deviations from the standard genetic code.

Example	codon	Usual value	Reads like:
Some types of yeast of the genus Candida	CUG	Leucine	Serene
Mitochondria, in particular Saccharomyces cerevisiae	CU(U, C, A, G)	Leucine	Serene
Mitochondria of higher plants	CGG	Arginine	tryptophan
Mitochondria (in all studied organisms without exception)	UGA	Stop	tryptophan
Mammalian mitochondria, Drosophila, S.cerevisiae and many simple	AUA	Isoleucine	Methionine = Start
prokaryotes	GUG	Valine	Start
Eukaryotes (rare)	CUG	Leucine	Start
Eukaryotes (rare)	GUG	Valine	Start
Prokaryotes (rare)	UUG	Leucine	Start
Eukaryotes (rare)	ACG	Threonine	Start
Mammalian mitochondria	AGC, AGU	Serene	Stop
Drosophila mitochondria	AGA	Arginine	Stop
Mammalian mitochondria	AG(A,G)	Arginine	Stop

The history of ideas about the genetic code

Nevertheless, in the early 1960s, new data revealed the failure of the "comma-free code" hypothesis. Then experiments showed that codons, considered by Crick to be meaningless, can provoke protein synthesis in a test tube, and by 1965 the meaning of all 64 triplets was established. It turned out that some codons are simply redundant, that is, a number of amino acids are encoded by two, four or even six triplets.

see also

Notes

1. Genetic code supports targeted insertion of two amino acids by one codon. Turanov AA, Lobanov AV, Fomenko DE, Morrison HG, Sogin ML, Klobutcher LA, Hatfield DL, Gladyshev VN. Science. 2009 Jan 9;323(5911):259-61.
2. The AUG codon encodes methionine, but also serves as a start codon - as a rule, translation begins from the first AUG codon of mRNA.
3. NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
4. jukes th, osawa s, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
5. Osawa S, Jukes TH, Watanabe K, Muto A (March 1992). "Recent evidence for evolution of the genetic code". microbiol. Rev. 56 (1): 229–64. PMID 1579111.
6. SANGER F. (1952). "The arrangement of amino acids in proteins.". Adv Protein Chem. 7 : 1-67. PMID 14933251 .
7. M. Ichas biological code. - World, 1971.
8. WATSON JD, CRICK FH. (April 1953). «Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid.". Nature 171 : 737-738. PMID 13054692 .
9. WATSON JD, CRICK FH. (May 1953). "Genetical implications of the structure of deoxyribonucleic acid.". Nature 171 : 964-967. PMID 13063483 .
10. Crick F.H. (April 1966). "The genetic code - yesterday, today, and tomorrow." Cold Spring Harb Symp Quant Biol.: 1-9. PMID 5237190.
11. G. GAMOW (February 1954). "Possible Relationship between Deoxyribonucleic Acid and Protein Structures.". Nature 173 : 318. DOI: 10.1038/173318a0 . PMID 13882203 .
12. GAMOW G, RICH A, YCAS M. (1956). "The problem of information transfer from the nucleic acids to proteins.". Adv Biol Med Phys. 4 : 23-68. PMID 13354508 .
13. Gamow G, Ycas M. (1955). STATISTICAL CORRELATION OF PROTEIN AND RIBONUCLEIC ACID COMPOSITION. ". Proc Natl Acad Sci U S A. 41 : 1011-1019. PMID 16589789 .
14. Crick FH, Griffith JS, Orgel LE. (1957). CODES WITHOUT COMMAS. ". Proc Natl Acad Sci U S A. 43 : 416-421. PMID 16590032.
15. Hayes B. (1998). "The Invention of the Genetic Code." (PDF reprint). American scientist 86 : 8-14.

Literature

• Azimov A. Genetic code. From the theory of evolution to the decoding of DNA. - M.: Tsentrpoligraf, 2006. - 208 s - ISBN 5-9524-2230-6.
• Ratner V. A. Genetic code as a system - Soros Educational Journal, 2000, 6, No. 3, pp. 17-22.
• Crick FH, Barnett L, Brenner S, Watts-Tobin RJ. General nature of the genetic code for proteins - Nature, 1961 (192), pp. 1227-32

Links

• Genetic code- article from the Great Soviet Encyclopedia

Wikimedia Foundation. 2010 .

Genetic code- a unified system for recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides. 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 20 types of amino acids in total. Of the 64 codons, three - UAA, UAG, UGA - do not encode amino acids, they were called nonsense codons, they perform the function of punctuation marks. Codon (coding trinucleotide) - a unit of the genetic code, a triplet of nucleotide residues (triplet) in DNA or RNA, encoding the inclusion of one amino acid. The genes themselves are not involved 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 bases of DNA, called codons. From 64

Gene properties. code
1) Tripletity: 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 triple by triplet without gaps, while neighboring triplets do not overlap.

88. Heredity and variability are the fundamental properties of the living. Darwinian understanding of the phenomena of heredity and variability.
heredity called the common 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 in the process of the historical development of the species and is manifested under certain environmental conditions.
Variability there is a 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 occur in a number of successive generations and populations.
Darwinian 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 variability. Darwin analyzed in detail the importance of heredity in the evolutionary process. He drew attention to cases of single-color 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. Comparing many breeds of animals and varieties of plants, Darwin noticed that within any kind of animals and plants, and in culture, within any variety and breed, there are no identical individuals. Darwin concluded that all animals and plants are characterized by variability.
Analyzing the material on the variability of animals, the scientist noticed that any change in the conditions of detention is enough to cause variability. Thus, by variability, Darwin understood the ability of organisms to acquire new characteristics under the influence of environmental conditions. He distinguished the following forms of variability:
Certain (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 are usually 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 indefinite influence of the conditions of existence 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 a ridge on the bone to which it is attached. In many wading birds, there is a correlation between neck length and limb length: long-necked birds also have long limbs.
Compensatory variability consists in the fact that the development of some organs or functions is often the cause of the oppression of others, i.e., an inverse correlation is observed, for example, between milkiness and fleshiness of cattle.

89. Modification variability. The reaction rate of genetically determined traits. Phenocopies.
Phenotypic variability covers changes in the state of directly signs that occur under the influence of developmental conditions or environmental factors. The range of modification variability is limited by the reaction rate. The resulting specific modification change in a trait is not inherited, but the range of modification variability is due to heredity. In this case, the hereditary material is not involved in the change.
reaction rate- this is the limit of the modification variability of the trait. The reaction rate 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 rate is a specific quantitative and qualitative characteristic of the genotype. There are signs with a wide reaction norm, a narrow () and an unambiguous norm. reaction rate has limits or boundaries for each biological species (lower and upper) - for example, increased feeding will lead to an increase in the mass of the animal, however, it will be within the normal reaction characteristic of this species or breed. The reaction rate is genetically determined and inherited. For different traits, the limits of the reaction norm vary greatly. For example, the value of milk yield, the productivity of cereals and many other quantitative traits have wide limits for the reaction norm, while the color intensity of most animals and many other qualitative traits have narrow limits. Under the influence of some harmful factors that a person does not encounter in the process of evolution, the possibility of modification variability, which determines the norms of the reaction, is excluded.
Phenocopies- changes in the 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 relationship between the result of the change and the influencing factor. The most complex genetic disorders of development are relatively easy to reproduce, while it is much more difficult to copy signs.

90. Adaptive nature of the modification. The role of heredity and environment in the development, training and education of a person.
Modification variability corresponds to habitat conditions, has an adaptive character. Such features 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 that occur 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, only the possibility of their formation within certain limits, called the reaction norm, is programmed in the organism's genotype. The reaction rate represents the limits of the modification variability of a trait allowed for a given genotype.
The degree of expression of the trait during the implementation of the genotype in various conditions is called expressivity. It is associated with the variability of the trait within the normal range of the reaction.
The same trait may appear in some organisms and be absent in others that have the same gene. The quantitative measure of the phenotypic expression of a gene is called penetrance.
Expressivity and penetrance are supported by natural selection. Both patterns must be kept in mind when studying heredity in humans. By changing the 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 burdened does not necessarily have to appear. Much depends on the conditions in which the person is. In some cases, the disease as a phenotypic manifestation of hereditary information can be prevented by diet or medication. The implementation of hereditary information depends on the environment. Being 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. A different nature of mutational changes: they are the result of changes in the structure of the DNA molecule, which causes a violation in the previously established process of protein synthesis. when mice are kept at elevated temperatures, their offspring are born with elongated tails and enlarged ears. Such a modification is adaptive in nature, since the protruding parts (tail and ears) play a thermoregulatory role in the body: an increase in their surface allows for an increase in heat transfer.

Human genetic potential is limited in time, and quite severely. If you miss the period of early socialization, it will fade away without having time to be realized. A striking example of this statement are the numerous cases when babies, by force of circumstances, fell into the jungle and spent several years among the animals. After their return to the human community, they could not fully catch up: to master speech, to acquire fairly complex skills of human activity, their mental functions of a person did not develop well. 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 education and training.

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

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

The interaction of heredity and environment in the development of a person plays an important role throughout his life. But it acquires special importance during the periods of formation of the organism: embryonic, infant, child, adolescent and youthful. It is at this time that an intensive process of development of the body and the 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 becomes generally recognized 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 value of combinative variability in ensuring the genotypic diversity of people: Systems of marriages. Medical genetic aspects of the family.
Combination variability associated with obtaining new combinations of genes in the genotype. This is achieved as a result of three processes: a) independent divergence of chromosomes during meiosis; b) their random combination during fertilization; c) gene recombination due to Crossing over. The hereditary factors (genes) themselves do not change, but new combinations of them arise, which leads to the appearance of organisms with other genotypic and phenotypic properties. Due 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 possibilities of adapting organisms to changing environmental conditions are expanding and thereby ensuring the survival of a group of organisms (populations, species) as a whole

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

Marriages can be: electoral, indiscriminate.

To the indiscriminate include panmix marriages. panmixia(Greek nixis - mixture) - marriages between people with different genotypes.

Selective marriages: 1. Outbreeding- marriages between people who do not have family ties according to a previously known genotype, 2.Inbreeding- marriages between relatives 3.Positively assortative- marriages between individuals with similar phenotypes between (deaf and dumb, short with short, tall with tall, weak-minded with weak-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 incest marriages are prohibited by law 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 genetic significance inbred marriages is highly negative. In such marriages, homozygotization is observed, the frequency of autosomal recessive diseases increases by 1.5-2 times. Inbred populations show inbreeding depression; the frequency increases sharply, the frequency of unfavorable recessive alleles increases, and infant mortality increases. Positive assortative marriages also lead to similar phenomena. Outbreeding has a positive genetic value. In such marriages, heterozygotization is observed.

92. Mutational variability, classification of mutations according to the level of change in the lesion of hereditary material. Mutations in sex and somatic cells.
mutation called a change due to the reorganization of reproducing structures, a change in its genetic apparatus. Mutations occur abruptly 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 transgenerations, affect the structure of the gene itself. Mutations can change sections of the DNA molecule of different lengths. The smallest area, the change of which leads to the appearance of a mutation, is called a muton. It can only be made up of a couple of nucleotides. A change in the sequence of nucleotides in DNA causes a change in the sequence of triplets and, ultimately, a program for protein synthesis. 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 in a change in the amount or redistribution of the hereditary material of chromosomes.
Reorganizations are divided into nutrichromosomal And interchromosomal. Intrachromosomal rearrangements consist in the loss of part of the chromosome (deletion), doubling or multiplication of some of its sections (duplication), turning a chromosome fragment by 180 ° with a change in the sequence of genes (inversion).
Genomic mutations associated with a change 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, in the general case 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 distinguish between mitotic and meiotic aneuploidy. A multiple decrease in the number of chromosome sets of somatic cells compared to a diploid one is called haploidy. The multiple attraction of the number of chromosome sets of somatic cells in comparison with the diploid one is called polyploidy.
These types of mutations are found both in germ cells and in somatic cells. Mutations that occur in germ cells are called generative. They are passed on to subsequent generations.
Mutations that occur in body cells at a particular stage of the individual development of an organism are called somatic. Such mutations are inherited by the descendants of only 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 base pairs. The smallest section of the DNA molecule, the change of which leads to a 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 outside of direct connection with any physical or chemical environmental factor.
If mutations are caused intentionally, by exposure to factors of a known nature, they are called induced. The agent that induces mutations is called mutagen.
The nature of mutagens is varied These are physical factors, chemical compounds. The mutagenic effect of some biological objects - viruses, protozoa, helminths - has been established when they enter the human body.
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 the gene pools of species in large numbers.
An indicator of the intensity of the mutation process is the mutation frequency, which is calculated on average for the 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.
Anti-mutation mechanisms.
The pairing of chromosomes in the diploid karyotype of eukaryotic somatic cells serves as a protection factor against the adverse consequences of gene mutations. The pairing of allele genes prevents the phenotypic manifestation of mutations if they are recessive.
The phenomenon of extracopying of genes encoding vital macromolecules contributes to the reduction of the harmful effects of gene mutations. An example is the genes for rRNA, tRNA, histone proteins, without which the vital activity of any cell is impossible.
These mechanisms contribute to the preservation of genes selected during evolution and, at the same time, the accumulation of various 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 a change in the number of chromosomes. Genomic mutations are heteroploidy, haploidy And polyploidy.
Polyploidy- an increase in the diploid number of chromosomes by adding whole sets of chromosomes as a result of a violation of meiosis.
In polyploid forms, there is an increase in the number of chromosomes, a multiple of the haploid set: 3n - triploid; 4n is a tetraploid, 5n is a pentaploid, etc.
Polyploid forms differ phenotypically 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.
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 a diploid one 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 appear in the phenotype. This explains the reduced viability of haploids.
heteroploidy. As a result of violations of mitosis and meiosis, the number of chromosomes can change and not become a multiple of the haploid set. The phenomenon when any of the chromosomes, instead of being a pair, is in a triple number, is called trisomy. If trisomy is observed on one chromosome, then such an organism is called a trisomic and its chromosome set is 2n + 1. Trisomy can be on any of the chromosomes and even on several. With double trisomy, it has a set of chromosomes 2n + 2, triple - 2n + 3, etc.
The opposite phenomenon trisomy, i.e. the loss of one of the chromosomes from a pair in a diploid set is called monosomy, the organism is monosomic; its genotypic formula is 2p-1. In the absence of two distinct chromosomes, the organism is a double monosomic with the genotypic formula 2n-2, and so on.
From what has been said, it is clear that aneuploidy, i.e. violation of the normal number of chromosomes, leads to changes in the structure and to a decrease in the viability of the organism. The greater the disturbance, the lower the viability. In humans, a violation of the balanced set of chromosomes entails disease states, collectively known as chromosomal diseases.
Origin mechanism genomic mutations is associated with the pathology of a violation of the normal divergence of chromosomes in meiosis, resulting in the formation of abnormal gametes, which leads to a 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. The basis of this method is the compilation and analysis of pedigrees. A pedigree is a diagram that reflects the relationships between family members. Analyzing pedigrees, they study any normal or (more often) pathological trait in the generations of people who are related.
Genealogical methods are used to determine the hereditary or non-hereditary nature of a trait, dominance or recessiveness, chromosome mapping, sex linkage, to study the mutation process. As a rule, the genealogical method forms the basis for conclusions in medical genetic counseling.
When compiling pedigrees, standard notation is used. The person with whom the study begins is the proband. The offspring of a married couple is called a sibling, siblings are called siblings, cousins ​​are called cousins, and so on. Descendants who have a common mother (but different fathers) are called consanguineous, and descendants who have a common father (but different mothers) are called consanguineous; if the 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 consolidated.
With the help of the genealogical method, the hereditary conditionality of the studied trait, as well as the type of its inheritance, can be established. When analyzing pedigrees for several traits, the linked nature of their inheritance can be revealed, which is used when compiling chromosome maps. This method allows one to study the intensity of the mutation process, to evaluate the expressivity and penetrance of the allele.
twin method. It consists in studying the patterns of inheritance of traits in pairs of identical and dizygotic twins. Twins are two or more children conceived and born by the same mother at almost the same time. There are identical and fraternal twins.
Identical (monozygous, identical) twins occur at the earliest stages of zygote cleavage, when two or four blastomeres retain the ability to develop into a full-fledged organism during isolation. Since the zygote divides by mitosis, the genotypes of identical twins, at least initially, are completely identical. Identical twins are always of the same sex and share the same placenta during fetal development.
Fraternal (dizygotic, non-identical) occur during the fertilization of two or more simultaneously mature eggs. 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 different-sex.
When comparing identical and fraternal twins raised in the same environment, one can draw a conclusion about the role of genes in the development of traits.
The twin method allows you to make reasonable conclusions about the heritability of traits: the role of heredity, environment and random factors in determining certain traits of a person
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.) Pre-gametic level
Implemented:
1. Sanitary control over production - exclusion of the influence of mutagens on the body.
2. The release of women of childbearing age from work in hazardous industries.
3. Creation of lists of hereditary diseases that are common in a certain
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 assisting in making the right decision about childbearing.
prenatal level
It consists in conducting prenatal (prenatal) diagnostics.
Prenatal diagnosis- This is a set of measures that is carried out in order to determine the hereditary pathology in the fetus and terminate this pregnancy. Prenatal diagnostic methods include:
1. Ultrasonic 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 biopsy. The method is based on taking chorionic villi, culturing cells and examining them using cytogenetic, biochemical and molecular genetic methods.
4. Amniocentesis– puncture of the amniotic sac through the abdominal wall and taking
amniotic fluid. It contains fetal cells that can be examined
cytogenetically or biochemically, depending on the presumed pathology of the fetus.
5. Cordocentesis- puncture of the vessels of the umbilical cord and taking the blood of the fetus. Fetal lymphocytes
cultivated and tested.
4. Neonatal level
At the fourth level, newborns are screened to detect autosomal recessive metabolic diseases in the preclinical stage, when timely treatment begins to ensure the normal mental and physical development of children.

Principles of treatment of hereditary diseases
There are the following types of treatment.
1. symptomatic(impact on the symptoms of the disease).
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 methods can be used in symptomatic and pathogenetic treatment.
· Correction malformations by surgical methods (syndactyly, polydactyly,
cleft upper lip...
Substitution therapy, the meaning of which is to introduce into the body
missing or insufficient biochemical substrates.
· Metabolism induction- the introduction into the body of substances that enhance the synthesis
some enzymes and, therefore, speed up the processes.
· Metabolic inhibition- the introduction into the body of drugs that bind and remove
abnormal metabolic products.
· diet therapy ( therapeutic nutrition) - the elimination from the diet of substances that
cannot be absorbed by the body.
Outlook: In the near future, genetics will develop intensively, although it is still
very widespread in crops (breeding, cloning),
medicine (medical genetics, genetics of microorganisms). In the future, scientists hope
use genetics to eliminate defective genes and eradicate transmitted diseases
by inheritance, be able to treat serious diseases such 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 that await 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 breeding 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, it becomes necessary to investigate 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 consists in studying chromosomes using a microscope. More often, mitotic (metaphase) chromosomes serve as the object of study, less often meiotic (prophase and metaphase) chromosomes. Cytogenetic methods are used when studying the karyotypes of individual individuals
Obtaining the material of the 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 gestation, an 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 the 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. An important role in the detection of hereditary diseases and the exact localization of damage to the hereditary material of the fetus is played by the use of DNA probes.
Currently, with the help of amniocentesis, all chromosomal abnormalities, over 60 hereditary metabolic diseases, maternal and fetal incompatibility for erythrocyte antigens are diagnosed.
The diploid set of chromosomes in a cell, characterized by their number, size and shape, is called karyotype. A normal human karyotype includes 46 chromosomes, or 23 pairs: of which 22 pairs are autosomes and one pair is sex chromosomes.
In order to make it easier to understand the complex complex of chromosomes that make up the karyotype, they are arranged in the form idiograms. IN idiogram Chromosomes are arranged in pairs in descending order, with the exception of the sex chromosomes. The largest pair was assigned No. 1, the smallest - No. 22. Identification of chromosomes only by size encounters great difficulties: a number of chromosomes have similar sizes. Recently, however, by using various kinds of dyes, a clear differentiation of human chromosomes along their length into bands stained by special methods and not stained has been established. The ability to accurately differentiate chromosomes is of great importance for medical genetics, as it allows you to accurately determine the nature of disorders in the human karyotype.
Biochemical method

99. Karyotype and idiogram of a person. Characteristics of the human karyotype is normal
and pathology.
Karyotype- a set of features (number, size, shape, etc.) of a complete set of chromosomes,
inherent in cells of a given biological species (species karyotype), a given organism
(individual karyotype) or line (clone) of cells.
To determine the karyotype, microphotography or a 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), while men have one X chromosome and the other Y (karyotype: 46, XY). Study
The karyotype is done using a technique called cytogenetics.
Idiogram- a schematic representation of the haploid set of chromosomes of an organism, which
arranged in a row in accordance with their sizes, in pairs in descending order of their sizes. An exception is made for the sex chromosomes, which stand out especially.
Examples of the most common chromosomal pathologies.
Down syndrome is a trisomy of the 21st pair of chromosomes.
Edwards syndrome is a trisomy of the 18th pair of chromosomes.
Patau syndrome is a trisomy of the 13th pair of chromosomes.
Klinefelter's syndrome is a polysomy of the X chromosome in boys.

100. Significance 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 the 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 to predict the risk of having diseased offspring. The recommendations given in medical genetic consultations regarding the conclusion of a marriage or the prognosis of the genetic usefulness of the offspring are aimed at ensuring that they are taken into account by the consulted persons, who voluntarily make the appropriate decision.
Cytogenetic (karyotypic) method. The cytogenetic method consists in studying chromosomes using a microscope. More often, mitotic (metaphase) chromosomes serve as the object of study, less often meiotic (prophase and metaphase) chromosomes. This method is also used to study sex chromatin ( barr bodies) Cytogenetic methods are used when studying 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 a change in the number of chromosomes or a violation of their structure. In addition, this method makes it possible to study the processes of mutagenesis at the level of chromosomes and karyotype. Its use in medical genetic counseling for the purposes of prenatal diagnosis of chromosomal diseases makes it possible to prevent the appearance of offspring with severe developmental disorders by timely termination of pregnancy.
Biochemical method consists in determining the activity of enzymes or the content of certain metabolic products in the blood or urine. Using this method, metabolic disorders are detected due to the presence in the genotype of an unfavorable combination of allelic genes, more often recessive alleles in the homozygous state. With the timely diagnosis of such hereditary diseases, preventive measures can avoid serious developmental disorders.
Population-statistical method. This method makes it possible to estimate the probability of the birth of persons with a certain phenotype in a given population group or in closely related marriages; calculate the carrier frequency 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., restrictions on the freedom of choice of spouses, for a person 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 traits, 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 racial formation.

101. Structural disorders (aberrations) of chromosomes. Classification depending on the change in genetic material. Significance for biology and medicine.
Chromosomal aberrations result from rearrangement of chromosomes. They are the result of a break in the chromosome, leading to the formation of fragments that are later reunited, but the normal structure of the chromosome is not restored. There are 4 main types of chromosomal aberrations: shortage, doubling, inversion, translocations, deletion- the loss of a certain part of the chromosome, which is then usually destroyed
shortages arise due to the loss of a chromosome of one or another site. Deficiencies in the middle part of the chromosome are called deletions. The loss of a significant part of the chromosome leads the organism to death, the loss of minor sections causes a change in hereditary properties. So. With a shortage of one of the chromosomes in corn, its seedlings are deprived of chlorophyll.
Doubling due to the inclusion of an extra, duplicating section of the chromosome. It also leads to the emergence of new features. So, in Drosophila, the gene for striped eyes is due to the doubling of a section of one of the chromosomes.
Inversions are observed when the chromosome is broken and the detached section is turned 180 degrees. If the break occurred 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 occur when a chromosome segment from one pair is attached to a non-homologous chromosome, i.e. chromosome from another pair. Translocation sections of one of the chromosomes is known in humans; it may be the cause of Down's disease. Most translocations affecting large sections of chromosomes make the organism unviable.
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 cells of the body, 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 overall physical and mental development. Chromosomal diseases are characterized by a combination of many congenital defects. Such a defect is the manifestation of Down syndrome, which is observed in the case of trisomy in a small segment of the long arm of chromosome 21. The picture of the cat's cry syndrome develops with the loss of a portion of the short arm of chromosome 5. In humans, malformations of the brain, musculoskeletal, cardiovascular, and genitourinary systems are most often noted.

102. The concept of species, modern views on speciation. View criteria.
View is a collection of individuals that are similar in terms of the criteria of the species to such an extent that they can
interbreed under natural conditions and produce fertile offspring.
fertile offspring- one that can reproduce itself. An example of infertile offspring is a mule (a hybrid of a donkey and a horse), it is sterile.
View criteria- these are signs 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 and biochemical - how organs and cells work.
Behavioral - behavior, especially at the time of reproduction.
Ecological - a set of environmental factors necessary for life
species (temperature, humidity, food, competitors, etc.)
Geographic - area (distribution area), i.e. the area in which the species lives.
Genetic-reproductive - the same number and structure of chromosomes, which allows organisms to produce fertile offspring.
View criteria are relative, i.e. one cannot judge the species by one criterion. For example, there are twin species (in the malarial mosquito, in rats, etc.). They do not differ morphologically from each other, but have a different number of chromosomes and therefore do not give offspring.

103. Population. Its ecological and genetic characteristics and role in speciation.
population- a minimal self-reproducing grouping of individuals of one 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.
population is 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. Population density tends to increase as population size increases.
Spatial structure The 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.
Sex structure reflects a certain ratio of males and females in a population.
Age structure reflects the ratio of different age groups in populations, depending on life expectancy, the time of onset of puberty, and the number of offspring.
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 said to be polymorphic at a given locus if it contains two or more alleles. If the locus is represented by a single allele, they speak of monomorphism. By examining many loci, one can determine the proportion of polymorphic ones among them, i.e. assess the degree of polymorphism, which is an indicator of the genetic diversity of a population.
Heterozygosity. An important genetic characteristic of a population is heterozygosity - the frequency of heterozygous individuals in a population. It also reflects genetic diversity.
Inbreeding coefficient. Using this coefficient, the prevalence of closely related crosses in the population is estimated.
Association of genes. The 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 the frequency of alleles. To quantify these differences, indicators 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 are interspersed with spaces where they are few or absent. As a result, more or less isolated populations arise in which random free crossing (panmixia) systematically occurs. Interbreeding with other populations is very rare and irregular. Thanks to panmixia, each population creates a gene pool characteristic of it, different from other populations. It is precisely 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 the isolation of populations and the gene pool, which differs due to their isolation from each other. The material for evolution is mutational variation, which begins in a population and ends with the formation of a species.

Chemical composition and structural organization of the DNA molecule.

Nucleic acid molecules are very long chains consisting of many hundreds and even millions of nucleotides. Any nucleic acid contains only four types of nucleotides. The functions of nucleic acid molecules depend on their structure, their constituent nucleotides, their number in the chain, and the sequence of the compound in the molecule.

Each nucleotide is made up of three components: a nitrogenous base, a carbohydrate, and phosphoric acid. IN compound each nucleotide DNA one of the four types of nitrogenous bases (adenine - A, thymine - T, guanine - G or cytosine - C) is included, as well as a deoxyribose carbon and a phosphoric acid residue.

Thus, DNA nucleotides differ only in the type of nitrogenous base.
The DNA molecule consists of a huge number of nucleotides connected in a chain in a certain sequence. Each type of DNA molecule has its own number and sequence of nucleotides.

DNA molecules are very long. For example, to write down the sequence of nucleotides in DNA molecules from one human cell (46 chromosomes), one would need a book of about 820,000 pages. The alternation of four types of nucleotides can form an infinite number of variants of DNA molecules. These features of the structure of DNA molecules allow them to store a huge amount of information about all the signs of organisms.

In 1953, the American biologist J. Watson and the English physicist F. Crick created a model for the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two strands interconnected and spirally twisted. It looks like a double helix. In each chain, four types of nucleotides alternate in a specific sequence.

Nucleotide DNA composition differs in different types of bacteria, fungi, plants, animals. But it does not change with age, it depends little on changes in the environment. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule obeys a certain rule, namely: adenine of one chain is always connected by two hydrogen bonds only with Thymine of the other chain, and guanine by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complement each other.

Nucleic acid molecules - DNA and RNA are made up of nucleotides. The composition of DNA nucleotides includes a nitrogenous base (A, T, G, C), a deoxyribose carbohydrate and a residue of a phosphoric acid molecule. The DNA molecule is a double helix, consisting of two strands connected by hydrogen bonds according to the principle of complementarity. The function of DNA is to store hereditary information.

Properties and functions of DNA.

DNA is a carrier of genetic information, written in the form of a sequence of nucleotides using the genetic code. DNA molecules are associated with two fundamental properties of living organisms - heredity and variability. During a process called DNA replication, two copies of the original chain are formed, which are inherited by daughter cells when they divide, so that the resulting cells are genetically identical to the original.

Genetic information is realized during gene expression in the processes of transcription (synthesis of RNA molecules on a DNA template) and translation (synthesis of proteins on an RNA template).

The sequence of nucleotides "encodes" information about various types of RNA: information, or template (mRNA), ribosomal (rRNA) and transport (tRNA). All these types of RNA are synthesized from DNA during the transcription process. Their role in protein biosynthesis (translation process) is different. Messenger RNA contains information about the sequence of amino acids in a protein, ribosomal RNA serves as the basis for ribosomes (complex nucleoprotein complexes, the main function of which is to assemble a protein from individual amino acids based on mRNA), transfer RNA deliver amino acids to the protein assembly site - to the active center of the ribosome, " creeping" along the mRNA.

Genetic code, its properties.

Genetic code- a method inherent in all living organisms to encode the amino acid sequence of proteins using a sequence of nucleotides. PROPERTIES:

1. Tripletity- a significant unit of the code is a combination of three nucleotides (triplet, or codon).
2. Continuity- there are no punctuation marks between the 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 certain codon corresponds to only one amino acid (however, the UGA codon in Euplotes crassus codes for two amino acids - cysteine ​​and selenocysteine)
5. Degeneracy (redundancy) Several codons can correspond to the same amino acid.
6. Versatility- the genetic code works in the same way 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 "Variations of the standard genetic code" section below).
7. Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical.

5. DNA autoreproduction. Replicon and its functioning .

The process of self-reproduction of nucleic acid molecules, accompanied by the transmission by inheritance (from cell to cell) of exact copies of genetic information; R. carried out with the participation of a set of specific enzymes (helicase<helicase>, which controls the unwinding of the molecule DNA, DNA-polymerase<DNA polymerase> I and III, DNA-ligase<DNA ligase>), passes through a semi-conservative type with the formation of a replication fork<replication fork>; on one of the chains<leading strand> the synthesis of the complementary chain is continuous, and on the other<lagging strand> occurs due to the formation of Dkazaki fragments<Okazaki fragments>; R. - high-precision process, the error rate in which does not exceed 10 -9 ; in eukaryotes R. can occur at several points on the same molecule at once DNA; speed R. eukaryotes have about 100, and bacteria have about 1000 nucleotides per second.

6. Levels of organization of the eukaryotic genome .

In eukaryotic organisms, the transcriptional regulation mechanism is much more complex. As a result of cloning and sequencing of eukaryotic genes, specific sequences involved in transcription and translation have been found.
A eukaryotic cell is characterized by:
1. The presence of introns and exons in the DNA molecule.
2. Maturation of i-RNA - excision of introns and stitching of exons.
3. The presence of regulatory elements that regulate transcription, such as: a) promoters - 3 types, each of which sits a specific polymerase. Pol I replicates ribosomal genes, Pol II replicates protein structural genes, Pol III replicates genes encoding small RNAs. The Pol I and Pol II promoters are upstream of the transcription initiation site, the Pol III promoter is within the framework of the structural gene; b) modulators - DNA sequences that enhance the level of transcription; c) enhancers - sequences that enhance the level of transcription and act regardless of their position relative to the coding part of the gene and the state of the starting point of RNA synthesis; d) terminators - specific sequences that stop both translation and transcription.
These sequences differ from prokaryotic sequences in their primary structure and location relative to the initiation codon, and bacterial RNA polymerase does not "recognize" them. Thus, for the expression of eukaryotic genes in prokaryotic cells, the genes must be under the control of prokaryotic regulatory elements. This circumstance must be taken into account when constructing vectors for expression.

7. Chemical and structural composition of chromosomes .

Chemical chromosome composition - DNA - 40%, Histone proteins - 40%. Non-histone - 20% a little RNA. Lipids, polysaccharides, metal ions.

The chemical composition of a chromosome is a complex of nucleic acids with proteins, carbohydrates, lipids and metals. The regulation of gene activity and their restoration in case of chemical or radiation damage occurs in the chromosome.

STRUCTURAL????

Chromosomes- nucleoprotein structural Elements of the cell nucleus, containing DNA, which contains the hereditary Information of the organism, are capable of self-reproduction, have a structural and functional individuality and retain it in a number of generations.

in the mitotic cycle, the following features of the structural organization of chromosomes are observed:

There are mitotic and interphase forms of the structural organization of chromosomes, mutually passing into each other in the mitotic cycle - these are functional and physiological transformations

8. Packing levels of hereditary material in eukaryotes .

Structural and functional levels of organization of the hereditary material of eukaryotes

Heredity and variability provide:

1) individual (discrete) inheritance and changes in individual characteristics;

2) reproduction in individuals of each generation of the entire complex of morphological and functional characteristics of organisms of a particular biological species;

3) redistribution in species with sexual reproduction in the process of reproduction of hereditary inclinations, as a result of which the offspring has a combination of characters that is different from their combination in the parents. Patterns of inheritance and variability of traits and their combinations follow from the principles of the structural and functional organization of genetic material.

There are three levels of organization of the hereditary material of eukaryotic organisms: gene, chromosomal and genomic (genotype level).

The elementary structure of the gene level is the gene. The transfer of genes from parents to offspring is necessary for the development of certain traits in him. Although several forms of biological variability are known, only a violation of the structure of genes changes the meaning of hereditary information, in accordance with which specific traits and properties are formed. Due to the presence of the gene level, individual, separate (discrete) and independent inheritance and changes in individual traits are possible.

The genes of eukaryotic cells are distributed in groups along the chromosomes. These are the structures of the cell nucleus, which are characterized by individuality and the ability to reproduce themselves with the preservation of individual structural features in a number of generations. The presence of chromosomes determines the allocation of the chromosomal level of organization of hereditary material. The placement of genes in chromosomes affects the relative inheritance of traits, makes it possible to influence the function of a gene from its immediate genetic environment - neighboring genes. The chromosomal organization of the hereditary material serves as a necessary condition for the redistribution of the hereditary inclinations of the parents in the offspring during sexual reproduction.

Despite the distribution over different chromosomes, the entire set of genes functionally behaves as a whole, forming a single system representing the genomic (genotypic) level of organization of hereditary material. At this level, there is a wide interaction and mutual influence of hereditary inclinations, localized both in one and in different chromosomes. The result is the mutual correspondence of the genetic information of different hereditary inclinations and, consequently, the development of traits balanced in time, place and intensity in the process of ontogenesis. The functional activity of genes, the mode of replication and mutational changes in the hereditary material also depend on the characteristics of the genotype of the organism or the cell as a whole. This is evidenced, for example, by the relativity of the property of dominance.

Eu - and heterochromatin.

Some chromosomes appear condensed and intensely colored during cell division. Such differences were called heteropyknosis. The term " heterochromatin". There are euchromatin - the main part of mitotic chromosomes, which undergoes a normal cycle of compactization decompactization during mitosis, and heterochromatin- regions of chromosomes that are constantly in a compact state.

In most eukaryotic species, the chromosomes contain both eu- and heterochromatic regions, the latter being a significant part of the genome. Heterochromatin located in the centromeric, sometimes in the telomeric regions. Heterochromatic regions were found in the euchromatic arms of chromosomes. They look like intercalations (intercalations) of heterochromatin into euchromatin. Such heterochromatin called intercalary. Compaction of chromatin. Euchromatin and heterochromatin differ in compactization cycles. Euhr. goes through a full cycle of compactization-decompactization from interphase to interphase, hetero. maintains a state of relative compactness. Differential staining. Different sections of heterochromatin are stained with different dyes, some areas - with some one, others - with several. Using various stains and using chromosomal rearrangements that break heterochromatin regions, many small regions in Drosophila have been characterized where the affinity for color is different from neighboring regions.

10. Morphological features of the metaphase chromosome .

The metaphase chromosome consists of two longitudinal strands of deoxyribonucleoprotein - chromatids, connected to each other in the region of the primary constriction - the centromere. Centromere - a specially organized section of the chromosome, common to both sister chromatids. The centromere divides the body of the chromosome into two arms. Depending on the location of the primary constriction, the following types of chromosomes are distinguished: equal-arm (metacentric), when the centromere is located in the middle, and the arms are approximately equal in length; unequal arms (submetacentric), when the centromere is displaced from the middle of the chromosome, and the arms are of unequal length; rod-shaped (acrocentric), when the centromere is shifted to one end of the chromosome and one arm is very short. There are also point (telocentric) chromosomes, they do not have one arm, but they are not in the human karyotype (chromosomal set). In some chromosomes, there may be secondary constrictions that separate a region called the satellite from the body of the chromosome.

Today it is no secret to anyone that the life program of all living organisms is written on the DNA molecule. The easiest way to think of a DNA molecule is as a long ladder. The vertical uprights of this ladder are made up of molecules of sugar, oxygen, and phosphorus. All important working information in the molecule is recorded on the rungs of the ladder - they consist of two molecules, each of which is attached to one of the vertical racks. These molecules, the nitrogenous bases, are called adenine, guanine, thymine, and cytosine, but they are usually referred to simply by the letters A, G, T, and C. The shape of these molecules allows them to form bonds - finished steps - of only a certain type. These are the bonds between the bases A and T and between the bases G and C (the pair formed in this way is called "pair of reasons"). There can be no other types of bonds in the DNA molecule.

Going down the steps along one strand of the DNA molecule, you get the sequence of bases. It is this message in the form of a sequence of bases that determines the flow of chemical reactions in the cell and, consequently, the characteristics of the organism that has this DNA. According to the central dogma of molecular biology, information about proteins is encoded on the DNA molecule, which, in turn, acting as enzymes ( cm. Catalysts and enzymes) regulate all chemical reactions in living organisms.

A strict correspondence between the sequence of base pairs in a DNA molecule and the sequence of amino acids that make up protein enzymes is called the genetic code. The genetic code was deciphered shortly after the discovery of the double-stranded structure of DNA. It was known that the newly discovered molecule informational, or matrix RNA (mRNA, or mRNA) carries information written on DNA. Biochemists Marshall W. Nirenberg and J. Heinrich Matthaei of the National Institutes of Health in Bethesda, Washington, DC, performed the first experiments that led to the unraveling of the genetic code.

They started by synthesizing artificial mRNA molecules consisting only of the repeating nitrogenous base uracil (which is analogous to thymine, "T", and forms bonds only with adenine, "A", from the DNA molecule). They added these mRNAs to test tubes with a mixture of amino acids, with only one of the amino acids in each tube labeled with a radioactive label. The researchers found that the mRNA artificially synthesized by them initiated protein formation in only one test tube, where the labeled amino acid phenylalanine was located. So they established that the sequence "-U-U-U-" on the mRNA molecule (and, therefore, the equivalent sequence "-A-A-A-" on the DNA molecule) encodes a protein consisting only of the amino acid phenylalanine. This was the first step towards deciphering the genetic code.

Today it is known that three base pairs of a DNA molecule (such a triplet is called codon) code for one amino acid in a protein. By performing experiments similar to the one described above, geneticists eventually deciphered the entire genetic code, in which each of the 64 possible codons corresponds to a specific amino acid.