History of genetics as a science. History of the development of genetics (briefly)

Genetics is the biological science of the heredity and variability of organisms and the methods of managing them.

Genetics can rightly be considered one of the most important areas of biology. It is the scientific basis for the development of practical breeding methods, i.e. creation of new breeds of animals, plant species, cultures of microorganisms with traits necessary for a person.

For thousands of years, man has used genetic methods to improve domestic animals and cultivated plants without understanding the mechanisms underlying these methods. Judging by a variety of archaeological data, already 6,000 years ago people understood that some physical characteristics could be transmitted from one generation to another. By selecting certain organisms from natural populations and crossing them with each other, man created improved varieties of plants and animal breeds that possessed the properties he needed.

The elementary discrete units of heredity and variability are genes.

The Czech monk Gregor Mendel is considered to be the father of genetics. He was a physics and science teacher in an ordinary high school, and all his free time gave to the cultivation of plants in the garden of the monastery. Mendel did this not out of gastronomic interests, but to study the patterns of inheritance of traits. Experiments on plant hybridization were carried out even before Mendel, but none of his predecessors made any attempts to somehow analyze their results.

Mendel took the seeds of peas with purple flowers and the seeds of a variety that had white flowers. When plants grew from them and bloomed, he removed the stamens from the purple flower and transferred the pollen of the white flower to its pistil. After the allotted time, seeds were formed, which Mendel again planted in his garden the following spring. New plants soon sprouted. The result exceeded all expectations: the plants turned out to be with purple flowers, among them there was not a single white one. Mendel repeated his experiments more than once, but the result was the same. So, hybrids always acquire one of the parent traits.

The most important result of Mendel's experiments: in hybrids obtained from crossing plants with different signs, there is no dissolution of signs, and one sign (stronger, or, as Mendel called it, dominant) suppresses another (weaker or recessive).

But Mendel did not stop there. He took and crossed among themselves the purple pea plants obtained as a result of this experiment. As a result, both purple and white flowers appeared from the buds. The sign of the white color, which had disappeared after the first crossing, reappeared. The most interesting thing was that there were exactly 3 times more plants with purple flowers than with white ones.

Similar results were obtained in four more experiments, and in all cases the ratio of dominant and recessive traits after the second crossing averaged 3:1

The knowledge possessed by Mendel was insignificant, but the conclusions he made were far ahead of their time. Mendel made an assumption that soon became the most important of the laws he discovered. He comes to the conclusion that germ cells (gametes) carry only one deposit of each of the traits and are free from other deposits of the same trait. This law was called the law of purity of gametes, which has not lost its significance even now. The study of heredity has long been associated with the idea of ​​its corpuscular nature. In 1866, Mendel suggested that the characteristics of organisms are determined by heritable units, which he called "elements". Later they were called "factors" and, finally, genes; it has been shown that genes are located on chromosomes, with which they are transmitted from one generation to another.

Despite the fact that much is already known about chromosomes and the structure of DNA, it is very difficult to define a gene, so far only three possible definitions of a gene have been formulated:

a) a gene as a unit of recombination.

Based on his work on the construction of Drosophila chromosome maps, Morgan postulated that a gene is the smallest section of a chromosome that can be separated from adjacent sections as a result of crossing over. According to this definition, a gene is a large unit, a specific region of the chromosome that determines one or another feature of an organism;

b) gene as a unit of mutation.

As a result of studying the nature of mutations, it was found that changes in traits arise due to random spontaneous changes in the structure of the chromosome, in the sequence of bases, or even in one base. In this sense, one could say that a gene is one pair of complementary bases in the DNA nucleotide sequence, i.e. the smallest region of a chromosome that can undergo a mutation.

c) gene as a unit of function.

Since it was known that the structural, physiological and biochemical characteristics of organisms depend on genes, it was proposed to define a gene as the smallest section of a chromosome that determines the synthesis of a certain product.

But as is often the case in science, research that could have marked the birth of a new direction in biology was forgotten for several decades. The real history of genetics began in 1900, when the patterns discovered by Mendel were again "discovered" by scientists. Three botanists, the Dutchman Hugo De Vries, the German K. Korrens and the Austrian K. Chermak, studied the patterns of inheritance of traits during crossing.

De Vries studied evening primrose, poppy and Datura and discovered the law of splitting characteristics in hybrids. Correns discovered the same splitting law, but only on corn, and Cermak discovered on peas. Then, scientists decided to study the world literature on these issues and came across Mendel's research. It turned out that they did not discover anything new; moreover, Mendel's conclusions were deeper than their own.

The fame of Mendel spread instantly. All over the world, there were immediately many followers who repeated his experience at various facilities. In scientific use, even a special term appeared - “Mendelian signs”, that is, signs that obey the laws of Mendel.

Genetics as a science solves the following problems: it studies the ways of storing genetic information in different organisms (viruses, bacteria, plants, animals and humans) and its material carriers; analyzes transmission methods hereditary information from one generation of cells and organisms to another; reveals the mechanisms and patterns of realization of genetic information in the process individual development and the impact on them of environmental conditions; studies patterns and mechanisms of variability and its role in the evolutionary process; finds ways to repair damaged genetic information.

Various research methods are used to solve problems.

1. Method of hybridological analysis. It allows you to identify patterns of inheritance of individual traits during sexual reproduction of organisms.

2. The cytogenetic method allows studying the karyotype of body cells and detecting genomic and chromosomal mutations.

3. The genealogical method involves the study of pedigrees of animals and humans and allows you to establish the type of inheritance of a particular trait, the zygosity of organisms and the likelihood of manifestation of traits in future generations.

4. The twin method is based on the study of the manifestation of signs in identical and fraternal twins. It allows you to identify the role of heredity and the environment in the formation of specific traits.

Lecture plan

The subject of genetics. The essence of the phenomena of heredity and variability.

Methods of genetics.

A brief history of the development of genetics.

Genetic research in the Republic of Belarus

Connection of genetics with other sciences.

The meaning of genetics.

Question. The subject of genetics. The essence of the phenomena of heredity and variability.

Genetics is the science of the heredity and variability of living organisms and methods of managing them; It is a science that studies the heredity and variability of the characteristics of living organisms.

Heredity- this is

1) the ability of organisms to generate their own kind;

2) the ability of organisms to transmit (inherit) their characteristics and qualities from generation to generation;

3) the preservation of certain variants of traits when changing generations.

Variability- this is the ability of organisms to change according to the characteristics of the body or its individual parts, as well as functions.

Variation is

1) the existence of signs in various forms(options);

2) the appearance of differences between organisms (parts of an organism or groups of organisms) according to individual characteristics.

The main types of trait inheritance

Direct Inheritance, in which variants of traits remain unchanged from generation to generation.

- during vegetative propagation of plants;

- during self-pollination in plants;

- when breeding purebred animals and cross-pollination of purebred plants.

Indirect inheritance is the type of inheritance that is observed in sexual reproduction of animals and seed propagation plants.

To study indirect inheritance, hybridization is necessary - the crossing of organisms that differ in genotype.

With indirect inheritance, some variants of traits appear in each generation (such traits are called dominant, "dominant"), while other options may temporarily "disappear" and then appear in subsequent generations (such traits are called recessive, "retreating").

Complex types of trait inheritance it is very difficult to predict the appearance of new variants of signs in advance. In some cases, “suddenly” there are new variants of traits that neither parents, nor grandparents, nor aunts and uncles had. Complex inheritance of traits is possible both on the basis of the influence of environmental conditions on the development of the organism, and as a result of the emergence of new genes or new combinations of genes present in the organism.

Question. Methods of genetics.

In genetics, as in other sciences, numerous methods are used in research. Genetics has its own specific research methods:

Hybridological analysis- the main method in which purposeful crossing of parents with certain traits is carried out and the manifestation of these traits in the generations of offspring is observed.

Principles of hybridological analysis:

1. Use as initial individuals (parents) of forms that do not give splitting when crossing, i.e. constant forms.

2. Analysis of the inheritance of individual pairs of alternative traits, that is, traits represented by two mutually exclusive options.

3. Quantitative accounting of forms split off in the course of successive crossings and the use of mathematical methods in processing the results.

4. Individual analysis of offspring from each parent.

5. Based on the results of crossing, a crossover scheme is compiled and analyzed.

Genealogical- consists in the analysis of pedigrees and allows you to determine the type of inheritance (dominant, recessive, autosomal or sex-linked) of the trait, as well as its monogenicity or polygenicity. Based on the information obtained, the probability of the manifestation of the studied trait in the offspring is predicted, which has great importance to prevent hereditary diseases.

cytogenetic- study of chromosomes: counting their number, description of the structure, behavior during cell division, as well as the relationship of changes in the structure of chromosomes with the variability of characters.

Biochemical- based on the study of the activity of enzyme systems. Activity is measured either by the activity of the enzyme itself, or by the amount of end products of the reaction that the enzyme controls. Studying the activity of enzyme systems makes it possible to identify gene mutations that are the causes of metabolic diseases, for example, phenylketonuria, sickle cell anemia.

Molecular- allows you to analyze DNA fragments, find and isolate individual genes, establish the nucleotide sequence (carry hereditary information).

question. A brief history of the development of genetics.

famous doctor Ancient Greece Hippocrates believed that in the egg cell, or in the body of the mother, there should be a small, but fully formed, preformed organism. These beliefs later became known as preformism (from Latin preforraatio - preformation). The dispute between the preformists was only about where exactly this organism is located - in the feminine or masculine principle.

The opposite views, according to which the organism develops from a structureless, homogeneous mass, first expressed by Aristotle, later received the development and name of epigenesis (from the Greek epi - after and genesis - development).

C. Darwin for the first time put biology on scientific basis. He showed that the basis of evolution and selection is the action of heredity, variability and selection. These provisions became the basis for all subsequent development of genetics.

First stage development of science.

It was marked by the discovery by G. Mendel (1865) of the discreteness (divisibility) of hereditary factors and the development of the hybridological method, the study of heredity, that is, the rules for crossing organisms and taking into account signs in offspring.

The significance of G. Mendel's discoveries was appreciated after his laws were rediscovered in 1900 by three biologists independently of each other: de Vries in Holland, K. Korrens in Germany and E. Cermak in Austria.

In 1901 -1903. Hugo de Vries put forward the mutational theory of variability, which played an important role in the further development of genetics.

The work of the Danish botanist was important Wilhelm Ludwig Johannsen, who studied patterns of inheritance in pure bean lines. He also formulated the concept of "population" (a group of organisms of the same species living and reproducing in a limited area), proposed to call Mendelian "hereditary factors" the term "gene", gave definitions of the concepts "genotype" and "phenotype".

Second phase

It is characterized by a transition to the study of the phenomena of heredity at the cellular level (cytogenetics). T. Boveri (1902-1907), W. Setton and E. Wilson (1902-1907) established the relationship between the Mendelian laws of inheritance and the distribution of chromosomes in the process of cell division (mitosis) and maturation of germ cells (meiosis).

Of decisive importance in substantiating the chromosomal theory of heredity were the studies carried out on fruit flies by the American geneticist T. G. Morgan and his collaborators (1910-1911).

Morgan also established patterns of inheritance of sex-linked traits.

The next step was to establish the chemical nature of chromosomal genes. Soviet geneticist N.K. Koltsov was one of the first to develop the idea of ​​their macromolecular nature (1927), and N.V. Timofeev-Resovsky with co-authors in the mid-30s. 20th century calculated the approximate size of the gene.

For the first time in 1925, Soviet microbiologists G.A. Nadson and G.S. Filippov showed that after irradiation of yeast cells ionizing radiation various radio races arise, the properties of which are reproduced in the offspring. In 1927, H.J. Muller, in precise experiments on Drosophila, taking into account the radiation dose, established the emergence of new hereditary mutations. Later I.A. Rapoport and Ch. Auerbach discovered the phenomenon of mutagenesis under the influence of chemicals.

Third stage

Reflects the achievements of molecular biology and is associated with the use of methods and principles exact sciences- physics, chemistry, mathematics, biophysics, etc. - in the study of life phenomena at the molecular level. Fungi, bacteria, and viruses have become objects of genetic research.

At this stage, the relationship between genes and enzymes was studied and the theory “one gene - one enzyme” was formulated (J. Beadle and E. Tatem, J. Lederberg, 1940): each gene controls the synthesis of one enzyme; the enzyme, in turn, controls one reaction from a whole series of biochemical transformations that underlie the manifestation of an external or internal sign of an organism.

In 1953, F. Crick and J. Watson, relying on the results of the experiments of geneticists and biochemists, on the data of X-ray diffraction analysis, created a structural model of DNA in the form of a double helix. The DNA model proposed by them is in good agreement with the biological function of this compound: the ability to self-double the genetic material and its stable preservation in generations - from cell to cell.

Although the history of genetics began in the 19th century, even ancient people noticed that animals and plants pass on their traits in a number of generations. In other words, it was obvious that heredity exists in nature. In this case, individual signs may change. That is, in addition to heredity, there is variability in nature. Heredity and variability are among the basic properties of living matter. For a long time(until the 19th-20th centuries) the true reason for their existence was hidden from man. This gave rise to a number of hypotheses that can be divided into two types: direct inheritance and indirect inheritance.

Adherents direct inheritance(Hippocrates, Lamarck, Darwin, etc.) assumed that information from each organ and each part of the body of the parent organism is transmitted to the daughter organism through certain substances (gemmules according to Darwin) that are collected in the reproductive products. According to Lamarck, damage or strong development of an organ would be directly transmitted to the next generation. Hypotheses indirect inheritance(Aristotle in the 4th century BC, Weismann in the 19th century) argued that the reproductive products are formed in the body separately and "do not know" about changes in the organs of the body.

In any case, both hypotheses were looking for a "substrate" of heredity and variability.

The history of genetics as a science began with the work of Gregor Mendel (1822-1884), who in the 60s conducted systematic and numerous experiments on peas, established a number of patterns of heredity, and was the first to suggest the organization of hereditary material. The correct choice of the object of study, the characteristics under study, as well as scientific luck allowed him to formulate three laws:

Mendel realized that the hereditary material is discrete, represented by individual inclinations that are transmitted to offspring. In addition, each deposit is responsible for the development of a certain feature of the organism. The sign is provided by a pair of inclinations that came with germ cells from both parents.

While scientific discovery Mendel was not given much importance. Its laws were rediscovered at the beginning of the 20th century by several scientists on different plants and animals.

In the 1980s, mitosis and meiosis were described, during which chromosomes are regularly distributed between daughter cells. At the beginning of the 20th century, T. Boveri and W. Setton came to the conclusion that the continuity of properties in a number of generations of organisms is determined by the continuity of their chromosomes. That is, for this period of time scientific world I understood in what structures the “substrate” of heredity lies.

W. Batson was discovered law of gamete purity, and the science of heredity and variability for the first time in history was named by him genetics. V. Johansen introduced into science the concepts (1909) genotype and phenotype. At that time, scientists had already realized that a gene is an elementary hereditary factor. But its chemical nature was not yet known.

In 1906 it was opened gene linkage phenomenon, including sex-linked inheritance of traits. The concept of genotype emphasized that the genes of an organism are not just a set of independent units of heredity, they form a system in which certain dependencies are observed.

In parallel with the study of heredity, the laws of variability were discovered. In 1901, de Vries laid the foundations for the theory of mutational variability associated with the occurrence of changes in chromosomes, which leads to changes in traits. A little later, it was discovered that they often occur when exposed to radiation, certain chemicals, etc. Thus, it was proved that chromosomes are not only a “substrate” of heredity, but also variability.

In 1910, largely generalizing earlier discoveries, T. Morgan's group developed chromosome theory:

Genes are located on chromosomes and are arranged linearly there.

Each chromosome has a homologous one.

From each parent, the offspring receives one of each homologous chromosome.

Homologous chromosomes contain the same set of genes, but the alleles of the genes may be different.

Genes on the same chromosome are inherited together() subject to their proximity.

Among other things, at the beginning of the 20th century, extrachromosomal, or cytoplasmic, heredity associated with mitochondria and chloroplasts was discovered.

Chemical analysis of chromosomes showed that they are composed of proteins and nucleic acids. In the first half of the 20th century, many scientists were inclined to believe that proteins are carriers of heredity and variability.

In the 1940s, a leap took place in the history of genetics. Research is moving to the molecular level.

In 1944, it was discovered that such a cell substance as is responsible for hereditary traits. DNA is recognized as the carrier of genetic information. A little later it was stated that one gene codes for one polypeptide.

In 1953, D. Watson and F. Crick deciphered the structure of DNA. It turned out that this double helix made up of nucleotides. They created a spatial model of the DNA molecule.

The following properties were later discovered (60s):

Each amino acid of a polypeptide is encoded by a triplet.(the three nitrogenous bases in DNA).

Each amino acid is encoded by one triplet or more.

Triplets do not overlap.

The reading starts from the starting triplet.

There are no "punctuation marks" in DNA.

In the 70s, another qualitative leap took place in the history of genetics - the development genetic engineering. Scientists begin synthesize genes, change genomes. At this time, actively studied molecular mechanisms underlying various physiological processes.

In the 90s genomes are sequenced(the sequence of nucleotides in DNA is deciphered) of many organisms. In 2003, the human genome sequencing project was completed. There are currently genomic databases. This makes it possible to comprehensively explore physiological features, diseases of humans and other organisms, as well as to determine the relationship between species. The latter allowed the systematics of living organisms to reach a new level.

The birth of genetics at the turn of the century (1900) was prepared by the entire previous development of biological science. 19th century entered the history of biology thanks to two great discoveries: the cell theory formulated by M. Schleiden and T. Schwann (1838), and the evolutionary teachings of C. Darwin (1859). Both discoveries played a decisive role in the development of genetics. The cell theory, which declared the cell the basic structural and functional unit of all living beings, aroused increased interest in the study of its structure, which later led to the discovery of chromosomes and a description of the process of cell division. In turn, Charles Darwin's theory concerned the most important properties of living organisms, which later became the subject of study of genetics - heredity and variability. Both theories in late XIX in. united by the idea of ​​the need for the existence of material carriers of these properties, which should be in the cells.

Until the beginning of the twentieth century. all hypotheses about the mechanisms of heredity were purely speculative. So, according to the theory of pangenesis by Ch. Darwin (1868), tiny particles- gemmules that circulate through the bloodstream and enter the germ cells. After the fusion of germ cells, in the course of the development of a new organism, a cell of the same type from which it originated is formed from each gemmul, possessing all the properties, including those acquired by parents during life. The roots of Darwin's views on the mechanism of transmission of traits from parents to offspring through blood lie in the natural philosophy of ancient Greek philosophers, including the teachings of Hippocrates (5th century BC).

Another speculative hypothesis of heredity was put forward in 1884 by K. Negeli (German). He suggested that a special substance of heredity takes part in the transfer of hereditary inclinations to offspring - idioplasm, consisting of molecules assembled in cells into large filamentous structures - micelles. Micelles are connected in bundles and form a network that permeates all cells. Idioplasm is possessed by both sex and somatic cells. The rest of the cytoplasm does not participate in the transfer of hereditary properties. Not being supported by facts, the hypothesis of K. Negeli, nevertheless, anticipated the data on the existence and structure of the material carriers of heredity.

For the first time, A. Weisman pointed out chromosomes as material carriers of heredity. In his theory, he proceeded from the conclusions of the German cytologist Wilhelm Roux (1883) about the linear arrangement of hereditary factors (chromatin grains) in chromosomes and the longitudinal splitting of chromosomes during division as a possible way of distributing hereditary material. The theory of "germ plasm" by A. Weismann was finally formalized in 1892. He believed that in organisms there is a special substance of heredity - "germ plasm". The material substrate of the germ plasm is the chromatin structures of the nuclei of germ cells. The germ plasm is immortal, it is transmitted through the germ cells to descendants, while the body of the organism - the soma - is mortal. The germ plasm consists of discrete particles - biophores, each of which determines a separate property of cells. Biophores are grouped into determinants - particles that determine the specialization of cells. They, in turn, are combined into structures of more high order(ids), from which chromosomes are formed (according to the terminology of A. Weisman -).

A. Weisman denied the possibility of inheriting acquired properties. The source of hereditary changes, according to his teaching, are the events that occur during the process of fertilization: the loss of part of the information (reduction) during the maturation of germ cells and the mixing of the determinants of the father and mother, leading to the emergence of new properties. The theory of A. Weisman had a huge impact on the development of genetics, determining the future direction of genetic research.

By the beginning of the twentieth century. real prerequisites for the development of genetic science were created. The rediscovery in 1900 of G. Mendel's laws played a decisive role. As early as 1865, the Czech amateur researcher, monk of the Brunn Monastery, Gregor Mendel formulated the basic laws of heredity. This became possible thanks to the development of the first scientific genetic method, which was called “hybridological”. It was based on a system of crossings, which makes it possible to reveal the patterns of inheritance of traits. Mendel formulated three laws and the rule of "purity of gametes", which will be discussed in detail in the next lecture. No less (and perhaps more) important was the fact that Mendel introduced the concept of hereditary inclinations (prototypes of genes), which serve as the material basis for the development of traits, and expressed a brilliant guess about their pairing as a result of the fusion of “pure” gametes.

Mendel's research and his views on the mechanism of inheritance were several decades ahead of the development of science. Even the speculative hypotheses about the nature of heredity discussed above were formulated later. Chromosomes have not yet been discovered and the process of cell division, which underlies the transmission of hereditary information from parents to offspring, has not been described. In this regard, contemporaries, even those who, like Ch. Darwin, were familiar with the works of G. Mendel, failed to appreciate his discovery. For 35 years it has not been claimed by biological science.

Justice triumphed in 1900, when the second rediscovery of Mendel's laws followed simultaneously and independently by three scientists: G. de Vries (Dutch), K. Correns (German) and E. Cermak (Austrian). By repeating Mendel's experiments, they confirmed the universal nature of the laws he discovered. Mendel was considered the founder of genetics, and since 1900 the development of this science began.

In the history of genetics, two periods are usually distinguished: the first is the period of classical, or formal, genetics (1900-1944) and the second is the period of molecular genetics, which continues to the present. The main feature of the first period is that the nature of the material carriers of heredity remained unknown. Introduced by the Danish geneticist W. Johansen, the concept of "gene" - an analogue of the Mendelian hereditary factor - was abstract. Here is a quote from his work of 1909: “The properties of an organism are determined by special, under certain circumstances separable from each other and therefore to a certain extent independent units or elements in germ cells, which we call genes. At the present time, no definite idea of ​​the nature of genes can be formed, we can only be content with the fact that such elements really exist. But are they chemical formations? We don't know anything about this yet." Despite the lack of knowledge about the physicochemical nature of the gene, it was during this period that the basic laws of genetics were discovered and genetic theories were developed that formed the foundation of this science.

The rediscovery of Mendel's laws in 1900 led to the rapid spread of his teachings and numerous, most often successful, attempts by researchers in different countries on different objects (chickens, butterflies, rodents, etc.) to confirm the universal nature of his laws. During these experiments, new patterns of inheritance were discovered. In 1906, the English scientists W. Batson and R. Pennet described the first case of deviation from Mendel's laws, later called gene linkage. In the same year, the English geneticist L. Doncaster, in experiments with a butterfly, discovered the phenomenon of linkage of a trait with sex. At the same time, at the beginning of the 20th century the study of persistent hereditary changes in mutations begins (G. de Vries, S. Korzhinsky), and the first works on population genetics appear. In 1908, G. Hardy and W. Weinberg formulated the basic law of population genetics on the constancy of gene frequencies.

But the most important studies of the period of classical genetics were the work of the outstanding American geneticist T. Morgan and his students. T. Morgan is the founder and head of the world's largest genetic school, from which a whole galaxy of talented geneticists emerged. In his research, Morgan first used the fruit fly Drosophila, which has become a favorite genetic object and continues to be so today. The study of the phenomenon of gene linkage, discovered by W. Betson and R. Pennett, allowed Morgan to formulate the main provisions of the chromosome theory of heredity, which we will discuss in detail below. The main thesis of this basic genetic theory was that genes are arranged in a linear order on the chromosome, like beads on a string. However, even in 1937, Morgan wrote that among geneticists there is no agreement on the point of view on the nature of the gene - whether they are real or abstract. But he noted that in any case the gene is associated with a specific chromosome and can be localized there by pure genetic analysis.

Morgan and his colleagues (T. Painter, K. Bridges, A. Sturtevant and others) carried out a number of other outstanding studies: the principle of genetic mapping was developed, the chromosome theory of sex determination was created, and the structure of polytene chromosomes was studied.

An important event in the period of classical genetics was the development of works on artificial mutagenesis, the first data on which were obtained in 1925 in the USSR by G.A. Nadson and T.S. Filippov in experiments on the irradiation of yeast cells with radium. Of decisive importance for the development of work in this direction were the experiments of the American geneticist H. Meller on the effect of X-rays on Drosophila and his development of methods for quantitatively accounting for mutations. The work of G. Meller caused a huge number of experimental studies using X-rays on various objects. As a result, their universal mutagenic effect was established. Later it was found that other types of radiation, such as UV, as well as high temperature and some chemical substances. The first chemical mutagens were discovered in the 1930s. in the USSR in the experiments of V.V. Sakharova, M.E. Lobasheva and S.M. Gershenzon and their collaborators. A few years later, this direction acquired a wide scope, especially thanks to the research of A.I. Rapoport in the USSR and S. Auerbach in England.

Research in the field of experimental mutagenesis has led to rapid progress in the knowledge of the mutation process and to the elucidation of a number of questions concerning the fine structure of the gene.

Another important area of ​​genetic research in the period of classical genetics concerned the study of the role of genetic processes in evolution. The fundamental works in this area belong to S. Wright, R. Fisher, J. Haldane and S.S. Chetverikov. With their work, they confirmed the correctness of the main provisions of Darwinism and contributed to the creation of a new modern synthetic theory of evolution, which is the result of a synthesis of Darwin's theory and population genetics.

Since 1940, the second period in the development of world genetics began, which was called molecular, in accordance with the leading position of this area of ​​genetic science. The main role in the rapid rise of molecular genetics was played by a close alliance of biologists with scientists from other fields of natural science (physics, mathematics, cybernetics, chemistry), on the wave of which a number of important discoveries were made. During this period, scientists established the chemical nature of the gene, determined the mechanisms of its action and control, and made many more important discoveries that turned genetics into one of the main biological disciplines that determine the progress of modern natural science. The discoveries of molecular genetics have not been refuted, but only revealed the underlying mechanisms of those genetic patterns that were revealed by formal geneticists.

The work of J. Beadle and E. Tetum (USA) found that mutations in the bread mold Neurospora crassa block various stages of cellular metabolism. The authors suggested that genes control the biosynthesis of enzymes. The thesis appeared: “one gene – one enzyme”. In 1944, a study on genetic transformation in bacteria, carried out by American scientists (O. Avery, K. Macleod and M. McCarthy), showed that DNA is the carrier of genetic information. This conclusion was later confirmed by studying the phenomenon of transduction (J. Lederberg and M. Zinder, 1952) - the transfer of information from one bacterial cell to another using phage DNA.

These studies determined the increased interest in the study of the structure of DNA, which resulted in the creation in 1953 of a model of the DNA molecule by J. Watson (Amer. biologist) and F. Crick (English chemist). It was called a double helix, because, according to the model, it is built from two polynucleotide chains twisted into a helix. DNA is a polymer whose monomers are nucleotides. Each nucleotide consists of a five-carbon deoxyribose sugar, a phosphoric acid residue, and one of four nitrogenous bases (adenine, guanine, cytosine, and thymine). This work played a major role in the further development of genetics and molecular biology.

On the basis of this model, a semi-conservative mechanism of DNA synthesis was first postulated (F. Crick), and then experimentally proved (M. Meselson and F. Stahl, 1957), in which the DNA molecule is divided into two single chains, each of which serves template for the synthesis of the daughter chain. The synthesis is based on the principle of complementarity, previously defined by E. Chargaff (1945), according to which the nitrogenous bases of two DNA strands are arranged in pairs opposite each other, and adenine combines only with thymine (A-T), and guanine with cytosine (G-C). One of the consequences of the creation of the model was the decoding genetic code- the principle of recording genetic information. Many scientific teams in different countries worked on this problem. Success came to Amer. geneticist M. Nirenberg ( Nobel laureate), in whose laboratory the first code word, the codon, was deciphered. This word became the YYY triplet, a sequence of three nucleotides with the same nitrogenous base - uracil. In the presence of an mRNA molecule consisting of a chain of such nucleotides, a monotonous protein was synthesized containing consecutively connected residues of the same amino acid, phenylalanine. Further decoding of the code was a matter of technology: using matrices with different combinations of bases in codons, scientists compiled a code table. All the features of the genetic code were determined: universality, tripletity, degeneracy and non-overlapping. The deciphering of the genetic code by its significance for the development of science and practice is compared with the discovery of nuclear energy in physics.

After deciphering the genetic code and determining the principle of recording genetic information, scientists thought about how information is transferred from DNA to protein. Research on this issue has ended. full description mechanism for the implementation of genetic information, which includes two stages: transcription and translation.

After determining the chemical nature of the gene and the principle of its action, the question arose of how the work of genes is regulated. It was first heard in the studies of the French biochemists F. Jacob and J. Monod (1960), who developed a scheme for regulating a group of genes that control the process of lactose fermentation in the E. coli cell. They introduced the concept of a bacterial operon as a complex that combines all genes (both structural and regulatory genes) that serve any link in metabolism. Later, the correctness of their scheme was proved experimentally in the study of various mutations affecting various structural units of the operon.

Gradually, a scheme was developed for the mechanism of regulation of eukaryotic genes. This was facilitated by the establishment of the discontinuous structure of some genes and the description of the splicing mechanism.

Influenced by progress in the study of the structure and function of genes in the early 70s. 20th century geneticists came up with the idea of ​​manipulating them, primarily by transferring them from cell to cell. Thus, a new direction of genetic research appeared - genetic engineering.

The basis for the development of this direction was made up of experiments, during which methods for obtaining individual genes were developed. In 1969, in the laboratory of J. Beckwith, the lactose operon was isolated from the chromosome of Escherichia coli using the phenomenon of transduction. In 1970, a team led by G. Korano was the first to carry out chemical synthesis gene. In 1973, a method was developed for obtaining DNA fragments - gene donors - using restriction enzymes that cut the DNA molecule. And, finally, a method was developed for obtaining genes based on the phenomenon of reverse transcription, discovered in 1975 by D. Baltimore and G. Temin. To introduce foreign genes into cells based on plasmids, viruses, bacteriophages and transposons (mobile genetic elements), various vectors were constructed - carrier molecules that carried out the transfer process. The complex of the vector with the gene was called the recombinant molecule. The first recombinant molecule based on phage DNA was designed in 1974 (R. Murray and D. Murray). In 1975, methods were developed for cloning cells and phages with inserted genes.

Already in the early 70s. the first results of experiments in the field of genetic engineering were obtained. Thus, a recombinant molecule containing two different antibiotic resistance genes (tetracycline and streptomycin) was introduced into an E. coli cell, after which the cell acquired resistance to both drugs.

Gradually, the set of vectors and introduced genes was expanded, and the technology of transfer was improved. This made it possible to widely use the methods of genetic engineering for industrial purposes (biotechnology), primarily in the interests of medicine and agriculture. Bacteria were designed to produce biologically active substances. This made it possible to establish on the required scale the synthesis of such drugs necessary for a person as insulin, somatostatin, interferon, tryptophan, etc. Created a large number of transgenic plants that have become owners of valuable properties (resistance to pests, drought, high protein content, etc.) as a result of the introduction of foreign genes into their genome.

In the 70s. work began on sequencing the genomes of various objects, from bacteriophages to humans.

Special attention deserves the international genetic program “Human Genome”, the purpose of which is the complete decoding of the human genetic code and mapping of its chromosomes. In the future, intensive development of a new field of medical genetics, gene therapy, is planned, which should help reduce the risk of harmful genes and, thereby, limit the genetic burden to the maximum.

History of the development of genetics in Russia

The development of genetics in Russia took place in the second decade of the 20th century. Yuri Alexandrovich Filipchenko was the founder of the first domestic school of geneticists. In 1916, at St. Petersburg University, he began to read a course of lectures entitled “The Teaching of Heredity and Evolution,” in which he gave the central place to the laws of Mendel and the studies of T. Morgan. He made an authorized translation of Morgan's book The Theory of the Gene. Scientific interests Yu.A. Filipchenko lay in the field of heredity and variability of qualitative and quantitative traits. He paid special attention to the statistical regularities of variability. Yu.A. Filipchenko wrote a number of excellent books, among them the textbook "Genetics", according to which several generations of biologists studied in our country.

In the same period, two more scientific genetic schools were formed: one at the Institute of Experimental Biology (Moscow) under the leadership of Nikolai Konstantinovich Koltsov, the other under the leadership of Nikolai Ivanovich Vavilov began to be created in Saratov, where he was elected a university professor, and was finally formed in Leningrad on the basis of the All-Union Institute of Plant Industry (VIR).

N.K. Koltsov headed the large Research Institute of Experimental Biology in Moscow. He was the first to express the idea of ​​the macromolecular organization of heredity carriers (chromosomes) and their self-duplication as a mechanism for the transmission of genetic information. Ideas N.K. Koltsov had strong influence on famous scientists period, not only biologists, but also physicists, whose studies of the structure of the gene led to the development of molecular genetics. From scientific school N.K. Koltsov, such major geneticists as A.S. Serebrovsky, B.L. Astaurov, N.P. Dubinin, N.V. Timofeev-Resovsky, V.V. Sakharov and others.

An outstanding geneticist and breeder N.I. Vavilov won wide recognition for his work in the study of world agriculture and plant resources. He is the author of the doctrine of the centers of origin and diversity of cultivated plants and the doctrine of immunity, as well as the law of homologous series in hereditary variability. In addition, he created a world collection of agricultural and industrial plants, including the famous collection of wheat varieties. N.I. Vavilov enjoyed great prestige not only among domestic but also among foreign scientists. In the one he created in Leningrad All-Union Institute Crop Production (VIR) brought together scientists from all over the world to work. Recognition of the merits of N.I. Vavilov was elected president of the International Genetic Congress, which took place in 1937 in Edinburgh. However, circumstances did not allow N.I. Vavilov to attend this congress.

A serious contribution to the development of theoretical genetics was made by the research of the professor of Moscow University Alexander Sergeevich Serebrovsky and his young colleagues N.P. Dubinina, B.N. Sidorova, I.I. Agola and others. In 1929, they made the discovery of the phenomenon of stepwise allelism in Drosophila, which was the first step towards the rejection of the idea that the gene was indivisible, which had been established among geneticists. The central theory of the structure of the gene was formulated, according to which the gene consists of smaller subunits - centers that can mutate independently of each other. These studies served as a stimulus for the development of work on the study of the structure and function of the gene, which resulted in the development of the modern concept of the complex internal organization of the gene. Later (in 1966) N.P. Dubinin was awarded the Lenin Prize.

By the beginning of the 40s. 20th century In the USSR, genetics was in its heyday. In addition to those mentioned above, it should be noted the works of B.L. Astaurov on gender regulation silkworm genetic methods; cytogenetic studies by G.A. Levitsky, works by A.A. Sapegina, K.K. Meister, A.R. Zhebraka, N.V. Tsitsina on genetics and plant breeding; M.F. Ivanov on genetics and animal breeding; V.V. Sakharova, M.E. Lobasheva, S.M. Gershenzon, I.A. Rapoport on chemical mutagenesis; S.G. Levita and S.N. Davidenkov on human genetics and the work of many other talented scientists.

However, the political situation of opposition to the capitalist world that had developed in the USSR by the beginning of World War II led to the persecution of scientists working in the field of genetics, which was declared an idealistic bourgeois science, and its adherents were declared agents of world imperialism. Repressions fell upon the heads of many famous scientists, including N.I. Vavilova, M.E. Lobasheva, G.D. Karpechenko, S.M. Gershenzon and many, many others. Genetics has been thrown back several decades. T.D. played a significant role in the collapse of genetic science. Lysenko. Being a simple agronomist, he could not rise to the level of classical genetics with its abstract ideas about the gene and therefore simply denied the laws of Mendel, Morgan's chromosome theory of heredity, the doctrine of mutations. Lysenko covered up his scientific inconsistency with generous promises of a rapid rise in agriculture with the help of the methods he propagated for altering plants under the influence of growing conditions, which earned I.V. Stalin. As a shield, Lysenko used the work of the outstanding breeder I.V. Michurin. Unlike world science, our genetics began to be called Michurin's. Such an "honor" led to the fact that Michurin was given the fame of an adherent of Lysenko's ideas, which did not leave the scientist even after the collapse of the latter's activities. In fact, I.V. Michurin was an outstanding practical breeder, fruit grower, who had never been involved in the development theoretical foundations genetic science.

Domestic science finally cleared itself of “Lysenkoism” only by the mid-1960s. Many of the scientists who suffered from repressions, those who managed to survive, including N.V. Timofeev-Resovsky, M.E. Lobashov, V.V. Sakharov and others. The traditions they preserved and the great potential inherent in their students contributed to the rapid advancement, although the lagging behind the world level, of course, made itself felt. Nevertheless, a new generation of domestic geneticists was rising, who were to bring this science to the previous level. And again, the ranks of world-famous scientists have replenished Russian names: A.N. Belozersky, V.A. Engelhardt, S.I. Alikhanyan, R.B. Khesina, A.S. Spirin, S.V. Shestakova, S.G. Inge-Vechtomova, Yu.P. Altukhov and many others.

However, new social upheavals caused by perestroika, which led to the outflow of scientific personnel abroad, again prevented our science from gaining an appropriate status. It remains to be hoped that the younger generation, relying on the foundation laid by previous luminaries, will be able to fulfill this noble mission.

Genetics refers to the biological sciences. Its name comes from the Latin word geneo (I give birth) or genus (kind), indicating that it studies the heredity of organisms.

Heredity is usually understood as the property of parents to transmit their characteristics and characteristics of their parents to the next generation. Heredity is inextricably linked with variability, and therefore genetics studies both of these properties of the organism, that is, it is the science of heredity and variability.

Genetics as a science is still very young, it has existed since 1900, when three scientists in different countries, Hugh de Vries (1848 - 1935) in Holland, Carl Correns (1864 - 1933) in Germany and Erich Cermak (1871 -1962) in Austria, they discovered patterns of splitting in the offspring of intraspecific hybrids of evening primrose, poppy, dope, and peas.

It turned out that the three botanists who discovered the patterns of splitting in the offspring of intraspecific hybrids only “rediscovered” the patterns of inheritance discovered back in 1865 Gregor Johann Mendel (1822 - 1884) , reported by him in February and March and published in the “Proceedings” of the Society of Naturalists in the city of Brunn (Brno, Austria-Hungary, present-day Czech Republic) in 1866 in the article “ Experiments on plant hybrids”.

As an independent science, genetics separated from biology in 1907 at the suggestion of the scientist William Batson (1861 - 1926) . They also suggested the name of the new science. Over the years, genetics has made amazing progress.

Usually the history of genetics is divided into stages of classical and molecular genetics. However, according to Nikolai Petrovich Dubinin (1907 - 1988) , in the development of genetics, three stages can be distinguished,

First stage- This is the era of classical genetics, which lasted from 1900 to 1930. (for the successes in classical genetics of our scientists, this period is sometimes called “Russian”). It was the time of the creation of the gene theory and the chromosome theory of heredity, the development of the doctrine of the phenotype and genotype, the interaction of genes, the genetic principles of individual selection in breeding were developed, the doctrine of the mobilization of the planet's genetic resources for the purposes of breeding was substantiated.

Second phase- 1930-1953 - stage of neoclassicism in genetics. The possibility of artificial changes in genes and chromosomes has been discovered - experimental mutagenesis; found that the - it is a complex system, divided into parts; substantiated the principles of population genetics and evolutionary genetics; created biochemical genetics, which studies the processes of biosynthesis in the cell and organism; evidence has been obtained that DNA molecules serve as the basis for genetic information; substantiated the principles of medical and radiation genetics. Enormous factual material was obtained, deepening the principles of classical genetics with a simultaneous revision of a number of old provisions.

Third stage- from 1953 to the present - the era of synthetic genetics, when the structure and genetic significance of the deoxyribonucleic acid (DNA) molecule was revealed. By this time, the development of the theory of the gene and the theory of mutations, biochemical and evolutionary genetics, human genetics and other branches of genetics had reached new frontiers and, having combined with molecular genetics, provided a synthetic approach to the problem of heredity.

In order to understand the development of genetics, it is necessary to make a short historical review, to dwell on the views of the first plant hybridizers, who played a large role in the history of the study of the phenomena of heredity.

Attempts of mankind to know the phenomena of heredity are rooted in antiquity. These phenomena can first of all be observed on the person himself and domestic animals. Even then it was clear that the participation of the male seed was necessary in the conception and birth of a person, therefore, ideas about the phenomena of development and heredity were associated with one or another solution to the question of the origin of this seed. Alchemoi (VI - beginning of the 5th century BC), physician and natural philosopher, believed that the seed comes from the brain; Democritus (470 -380 BC) believed that the seed comes from all parts of the body, also believed Hippocrates (V century BC). Diogenes (V century BC) believed that the seed is formed from the bark. Aristotle (384 - 322 BC) believed that the seed is formed from the blood. He was aware of crosses between different species. Titus Lucretius Kar (c. 98-55 BC) in his poem “On the Nature of Things”, he argued that “children always depend on the double seed”: “For often fathers in their own body hide many origins in a diverse mixture, from generation to generation from fathers to fathers by inheritance. This is how Venus produces children by drawing lots, and she revives ancestors, hair, voice, face from her descendants.

A.E. Gaisinovich indicates a certain anticipation by Lucretius of the concept of hereditary factors (“originals”), which determine the transmission to descendants of individual features characteristic of ancestors, and their independent combination (“drawing lots”) on the basis of pure chance. Thus, Lucretius, as it were, anticipated the patterns established by G. Mendel.

The evolution of ideas about the field and reproduction in plants proceeded quite differently. It has been established that not only the ancient Greeks and Romans knew about the existence of sexes in plants ( Herodotus, Theophrastus, Pliny ), but even earlier (more than 2000 BC), the Babylonians and Assyrians carried out artificial pollination of date palms. Aristotle believed that in "plants the female sex is not separated from the male", he knew about the existence of dioecious plants. Theophrastus , student Aristotle (372 - 287 BC), had extensive knowledge of plants, described the structure of female flowers and the process of pollination in many plants.

No matter how meager and contradictory the knowledge of ancient authors about the field in plants was, they in many respects anticipated the science of modern times. Their knowledge was borrowed by the Arabs. For European science, this knowledge was lost until the 17th century. And practice far outstripped theory, which for many centuries was under a certain influence of religious and philosophical teachings, which in a number of cases prevented the recognition of even the obvious truth.

In 1694 Rudolf Jacob Camerarius (1665 - 1721) discovered male and female organs in plants and the need for pollination to form fruits. He immediately understood the significance of his discovery regarding the possibility of artificial production of hybrids. He wrote:

“The news here is the difficult question: can a female plant be fertilized by a male plant of another species, for example, female cannabis with male hops and so on; will the embryo learn and how much it is changed”.

Even earlier in the 16th century in America, the attention of Europeans was attracted by the “Indian cereal” - corn. Already the first observations showed that there are grains of various colors in the cobs: blue, yellow, red, white. This amazing phenomenon was considered as an incomprehensible game of nature.

At the first stage of the development of the doctrine of hybridization, the attention of scientists and breeders was fixed on the problem of sexes in plants;

hybridization was considered precisely from the point of view of proving their existence, the participation of male and female sexes in fertilization and the transmission of both characters to offspring.

Thomas Fairchild, an English horticulturist, created in 1717 the first artificial plant hybrid between Dianthus caryophyllus(red carnation) and D. barbatus(William-fragrant). The hybrid resembled a transitional plant between the parents. This first "vegetable mule" made a great impression on his contemporaries and became widely known.

Experiments made a special impression on contemporaries.

I. G. Gledich(1714 - 1786), director of the Berlin Botanical Garden, who pollinated a pistillate palm tree in 1749 with male palm pollen sent from Leipzig. The resulting seeds were sown in 1750 and gave seedlings, that is, the presence of sexes in plants was proved.

In 1721 a prominent botanist Philip Miller (1691 - 1771) observed spontaneous hybridization of cabbage varieties.

American botanist J. Bartram (1701 - 1774) in 1739 conducted experiments on crossing several species of the same genus Lichens and received outlandish mixed colors of flowers.

Extremely importance had questions about the sexual reproduction of plants for Carl Linnaeus (1707 - 1778). His taxonomy of plant classes was based on a classification based on the organs of fruit formation. For Linnaeus, the main criterion for the characteristics of a species was their hereditary invariance during sexual reproduction.

In 1760 Joseph Gottlieb Kelreuter (1733 -1806) began his experiments on hybridization. By this time, the presence of sexes in plants had already been established, the possibility of artificial pollination and hybridization had been proved, and their basic techniques had been developed. I. Kelreuter considers hybrids to be something in between the parental forms. He was the first to establish the phenomenon of heterosis, to apply analyzing crossing, but failed to penetrate deeply into the essence of the phenomena he observed.

Numerous experiments and studies on hybrids have raised the question of species before natural scientists: can hybrids arise between species and is the number of species constant?

Thomas Andrew Knight(1759 - 1838) was engaged in hybridization fruit trees, observed the dominance of traits in the color of peas. Like Kellreuter, he noted the powerful development of the first generation of hybrids, established the principles of pollination, which Darwin later called the law, now known as “ Knight-Darwin's law”:

“Nature tends to ensure that sexual intercourse takes place between neighboring plants of the same species.”

Working with bulbous, William Herbert (1778 - 1847), rector of Manchester Cathedral, in 1822 came to the conclusion that there were not always as many species as there are now; therefore, not only varieties, but also species occurred in different time over the centuries from a few original genera influenced by climate, soil and interbreeding.

In 1852 he began his research on hybridization Charles Naudin (1815 - 1899). He shares the doctrine of the variability of species, elucidates the phenomenon of dominance, believing that hybrids receive characteristics from the father and mother, but in different quantities. S. Noden came very close to understanding the patterns of heritability, but many of his discoveries were semi-intuitive. Its main merit S. Noden believed that his work opens up new ways to define the species and its boundaries: "There is no qualitative difference between species, races and varieties."

The basic laws of heredity were discovered Gregor Johann Mendel (1822 - 1884), monk of the Augustinian monastery from Austrian city Brunne (now Brno, Czech Republic). He was born into a peasant family in Heinzendorf, and received his primary education at a local school. In 1840 he graduated from the gymnasium, and in 1842 - the philosophical school in Olmutz. In 1843, G. Mendel entered the ancient Augustinian monastery of Starobryunsky, where he was initiated into novices under the name of Gregor. The craving for science makes him bother about entering the University of Vienna. By permission of Bishop G. Mendel enters the university as a volunteer, where for four semesters (1851 - 1853) he listened to experimental mathematics, physics, higher mathematics, chemistry, zoology, botany, physiology, phytopathology and entomology. Returning to the monastery, G. Mendel in 1854, he entered the real school in Brunn as a teacher of physics and natural history. At the same time, he was entrusted with the management of the natural history collections of the school. March 30, 1868 G. Mendel was elected prelate of the monastery.

G. Mendel undertakes to study the question of the number of pollen grains involved in fertilization. And, having pollinated with one single pollen grain of Mirabilis jalapa, G. Mendel received 18 well-developed seeds and from them the same number of plants, most of which developed as magnificently as the plants that occurred from self-pollination. Then he moves on to experiments with peas.

Around 1854, G. Mendel began to experiment with peas (Pisum sativum). In 1856, he conducted the first experiments on crossing different varieties of peas in order to find out how the individual characteristics of this organism are inherited. Experiments were carried out until 1863. In 1865, the results of the experiments were reported at two meetings - February 8 and March 8. Brief abstracts of G. Mendel's reports were published in Brunn in the Novosti newspaper on February 9 and March 10, 1865. At the end of 1866, by decision of the members of the Society, the work was published in the “Proceedings” of the Society in Brunn (Brno) and was called “Experiments on Plant Hybrids”. For his experiments, G. Mendel subjected 34 varieties of peas to a two-year test, receiving from each of them two generations of plants. Of these, he selected 22 varieties of peas that have alternative differences in 7 features: the shape of the seeds (smooth and wrinkled), the color of their endosperm (yellow or green), their peel (white or brown), the shape of the beans (convex or intercepted), their color when immature (yellow or green), arrangement of flowers (axillary or apical), plant height (tall or dwarf).

He became convinced that they are hereditarily pure forms, since in a number of offspring they did not give any deviations from the standard characteristics of the variety. Having crossed between plants that differ in one trait, having crossed the resulting offspring, he formulated two laws of heredity. To these laws a third was added after the crossing of plants differing in two characters.