The first transgenic plants (tobacco plants with inserted genes from microorganisms) were obtained in 1983. The first successful field trials of transgenic plants (tobacco plants resistant to viral infection) were carried out in the USA already in 1986.
After passing all the necessary tests for toxicity, allergenicity, mutagenicity, etc. The first transgenic products were commercialized in the US in 1994. These were Calgen's delayed-ripening Flavr Savr tomatoes and Monsanto's herbicide-resistant soybeans. Already after 1-2 years, biotech companies put on the market a number of genetically modified plants: tomatoes, corn, potatoes, tobacco, soybeans, rapeseed, marrows, radishes, cotton.
Currently, hundreds of commercial firms around the world with a combined capital of more than one hundred billion dollars are involved in obtaining and testing genetically modified plants. In 1999, transgenic plants were planted on a total area of about 40 million hectares, which is larger than the size of a country like the UK. In the US, genetically modified crops (GM Crops) now account for about 50% of corn and soybean crops and more than 30-40% of cotton crops. This suggests that genetically engineered plant biotechnology has already become an important industry for the production of food and other useful products, attracting significant human resources and financial flows. In the coming years, a further rapid increase in the area occupied by transgenic forms of cultivated plants is expected.
The first wave of transgenic plants approved for practical use contained additional genes for resistance (to diseases, herbicides, pests, spoilage during storage, and stresses).
The current stage in the development of plant genetic engineering has been called "metabolic engineering". At the same time, the task is not so much to improve certain existing qualities of the plant, as in traditional breeding, but to teach the plant to produce completely new compounds used in medicine, chemical production and other fields. These compounds can be, for example, special fatty acids, beneficial proteins with a high content of essential amino acids, modified polysaccharides, edible vaccines, antibodies, interferons and other “drug” proteins, new environmentally friendly polymers, and much, much more. The use of transgenic plants makes it possible to establish a large-scale and cheap production of such substances and thereby make them more accessible for wide consumption.
Improving the quality of plant storage proteins
The storage proteins of major cultivated species are encoded by a family of closely related genes. The accumulation of seed storage proteins is a complex biosynthetic process. The first genetic engineering attempt to improve the property of one plant by introducing a storage protein gene from another was carried out by D. Kemp and T. Hall in 1983 in the USA. The bean phaseolin gene was transferred into the sunflower genome using a Ti plasmid. The result of this experiment was only a chimeric plant, called sanbin. Immunologically related phaseolin polypeptides were found in sunflower cells, which confirmed the fact of gene transfer between plants belonging to different families
Later, the phaseolin gene was transferred to tobacco cells: in regenerated plants, the gene was expressed in all tissues, although in small amounts. The nonspecific expression of the phaseolin gene, as in the case of its transfer to sunflower cells, is very different from the expression of this gene in mature bean cotyledons, where phaseolin accounted for 25-50% of the total protein. This fact indicates the need to preserve other regulatory signals of this gene during the construction of chimeric plants and the importance of controlling gene expression in the process of plant ontogeny.
The gene encoding the maize storage protein, zein, after its integration into T-DNA, was transferred into the sunflower genome as follows. Agrobacterium strains containing Ti plasmids with the zein gene were used to induce tumors in sunflower stems. Some of the obtained tumors contained mRNA synthesized from maize genes, which gives grounds to consider these results as the first evidence of the transcription of a monocot gene in a dicot. However, the presence of zein protein in sunflower tissues was not detected.
A more realistic task for genetic engineering is to improve the amino acid composition of proteins. As is known, in the storage protein of most cereals there is a deficiency of lysine, threonine, tryptophan, in legumes - methionine and cysteine. The introduction of additional amounts of deficient amino acids into these proteins could eliminate the amino acid imbalance. Traditional breeding methods have succeeded in significantly increasing the content of lysine in the storage proteins of cereals. In all these cases, part of the prolamins (alcohol-soluble storage proteins of cereals) was replaced by other proteins containing a lot of lysine. However, in such plants, the grain size decreased and the yield decreased. Apparently, prolamins are necessary for the formation of normal grain, and their replacement by other proteins negatively affects the yield. Given this circumstance, to improve the quality of grain storage protein, a protein is needed that not only has a high content of lysine and threonine, but can also fully replace a certain part of the prolamins during grain formation.
Plants can also produce animal proteins. Thus, insertion into the genome of Arabidopsis thaliana and Brassica napus of a chimeric gene consisting of a part of the Arabidopsis 25-protein gene and the coding part for the neuropeptide enkephalin led to the synthesis of the chimeric protein up to 200 ng per 1 g of seed. Two structural protein domains were linked by a sequence recognized by trypsin, which made it possible to further easily isolate pure enkephalin.
In another experiment, after crossing transgenic plants, in one of which the gene for the gamma subunit was inserted, and in the second, the gene for the kappa subunit of immunoglobulin, it was possible to obtain the expression of both chains in the offspring. As a result, the plant formed antibodies, which constituted up to 1.3% of the total leaf protein. It has also been shown that fully functional secretory monoclonal immunoglobulins can be assembled in tobacco plants. Secretory immunoglobulins are usually secreted into the oral cavity and stomach of humans and animals and serve as the first barrier to intestinal infections. In the work mentioned above, monoclonal antibodies were produced in plants that were specific for Streptococcus mutans, bacteria that cause dental caries. It is assumed that on the basis of such monoclonal antibodies produced by transgenic plants, it will be possible to create a truly anti-caries toothpaste. Of other animal proteins of medical interest, the production of human β-interferon in plants has been shown.
Approaches have also been developed to obtain bacterial antigens in plants and use them as vaccines. A potato expressing oligomers of the non-toxic cholera β-toxin subunit was obtained. These transgenic plants could be used to produce a cheap cholera vaccine.
Fats
Fatty acids, the main component of vegetable oil, are the most important raw materials for obtaining various kinds of chemicals. In their structure, these are carbon chains that have different physicochemical properties depending on their length and the degree of saturation of carbon bonds. In 1995, experimental verification was completed and permission was obtained from the US federal authorities for the cultivation and commercial use of transgenic rapeseed plants with a modified composition of vegetable oil, including, along with conventional 16- and 18-membered fatty acids, also up to 45% of 12-membered fatty acids. - laureate. This substance is widely used for the production of washing powders, shampoos, and cosmetics.
The experimental work consisted in the fact that the specific thioesterase gene was cloned from the plant Umbellularia califomica, where the content of laurate in the seed fat reached 70%. The structural part of the gene of this enzyme, under the control of the promoter-terminator of the protein gene specific for the early stage of seed formation, was inserted into the genome of rapeseed and Arabidopsis, which led to an increase in the content of laurate in the oil of these plants.
Among other projects related to changing the composition of fatty acids, one can mention works aimed at increasing or decreasing the content of unsaturated fatty acids in vegetable oil. Of interest are experiments with petroselinic acid, an isomer of oleic acid, where the double bond is behind the sixth carbon member. This fatty acid is part of the composition of coriander oil and determines its higher melting point (33°C), while in the presence of oleic acid, the melting point is only 12°C. It is assumed that after the transfer of genes that determine the synthesis of petroselinic acid into plants - producers of vegetable oil, it will be possible to produce dietary margarine containing an unsaturated fatty acid. In addition, it is very easy to obtain laurate from petroselinic acid by oxidation with ozone. Further study of the specifics of the biochemical synthesis of fatty acids, apparently, will lead to the ability to control this synthesis in order to obtain fatty acids of various lengths and degrees of saturation, which will significantly change the production of detergents, cosmetics, confectionery, hardeners, lubricants, drugs, polymers. , diesel fuel and much more, which is associated with the use of hydrocarbon raw materials.
Polysaccharides
Work is underway to create transgenic potato plants and other starch-accumulating crops, in which this substance will be mainly in the form of amylopectin, that is, a branched form of starch, or mainly only in the form of amylose, that is, linear forms of starch. The solution of amylopectin in water is more liquid and transparent than that of amylose, which, when interacting with water, forms a rigid gel. So, for example, starch, consisting mainly of amylopectin, is likely to be in demand in the market of manufacturers of various nutritional mixtures, where modified starch is currently used as a filler. The genomes of plastids and mitochondria can also undergo genetic modification. Such systems can significantly increase the content of the product in the transgenic material.
Creation of herbicide-resistant plants
In new, intensive agricultural technologies, herbicides are used very widely. It's related to that. that the former environmentally hazardous broad-spectrum herbicides, which are toxic to mammals and persist in the external environment for a long time, are being replaced by new, more advanced and safe compounds. However, they have a drawback - they inhibit the growth of not only weeds, but also cultivated plants. Such highly effective herbicides as glyphosate, atrazines are intensively studied to identify the mechanism of tolerance to them of some weeds. Thus, in fields where atrazine is widely used, atrazine-resistant biotypes often appear in many plant species.
The study of the herbicide resistance mechanism in order to obtain cultivated plants with this trait by genetic engineering includes the following steps: identification of biochemical targets of herbicide action in a plant cell; selection of organisms resistant to a given herbicide as sources of resistance genes; cloning of these genes; introduction of them into cultivated plants and the study of their functioning
There are four fundamentally different mechanisms that can provide resistance to certain chemical compounds, including herbicides: transport, elimination, regulatory, and contact. The transport mechanism of resistance consists in the impossibility of penetration of the herbicide into the cell. Under the action of the elimination mechanism of resistance, substances that have entered the cell can be destroyed with the help of inducible cellular factors, most often degrading enzymes, and also undergo one or another type of modification, forming inactive products that are harmless to the cell. With regulatory resistance, a protein or cell enzyme that is inactivated under the action of a herbicide begins to be intensively synthesized, thus eliminating the deficiency of the desired metabolite in the cell. The contact mechanism of resistance is provided by a change in the structure of the target (protein or enzyme), the interaction with which is associated with the damaging effect of the herbicide.
It has been established that the trait of herbicide resistance is monogenic, that is, the trait is most often determined by a single gene. This greatly facilitates the possibility of using recombinant DNA technology to transfer this trait. Genes encoding various herbicide degradation and modification enzymes can be successfully used to create herbicide-resistant plants by genetic engineering.
Traditional breeding methods for creating herbicide-resistant varieties are very, time-consuming and ineffective. The herbicide glyphosate (commercial name Roundup), which is the most widely used abroad, inhibits the synthesis of the most important aromatic amino acids by acting on the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP-synthase). Known cases of resistance to this herbicide are associated either with an increase in the level of synthesis of this enzyme (regulatory mechanism) or with the appearance of a mutant enzyme insensitive to glyphosphate (contact mechanism). The EPSP synthase gene was isolated from glyphosphate-resistant plants and placed under the cauliflower mosaic virus promoter. Using the Ti plasmid, this genetic construct was introduced into petunia cells. In the presence of one copy of the gene in plants regenerated from transformed cells, the enzyme was synthesized 20–40 times more than in the original plants, but resistance to glyphosphate increased only 10 times.
Atrazine is one of the most common herbicides used in the treatment of crops. It inhibits photosynthesis by binding to one of the photosystem II proteins and stopping electron transport. Herbicide resistance results from point mutations in this plastoquinone-binding protein (replacement of serine by glycine), as a result of which it loses its ability to interact with the herbicide. In a number of cases, it was possible to transfer the mutant protein gene into atrazine-sensitive plants using a Ti plasmid. The resistance gene integrated into the plant chromosome was provided with a signal sequence that ensured the transport of the synthesized protein into chloroplasts. The chimeric plants showed significant resistance to atrazine concentrations that caused the death of control plants with the wild-type protein gene. Some plants are able to inactivate atrazine by cleavage of the chlorine residue by the enzyme glutathione-S-transferase. The same enzyme also inactivates other related herbicides of the triazine series (propazine, simazine, etc.).
There are plants whose natural resistance to herbicides is based on detoxification. Thus, plant resistance to chlorsulfuron can be associated with the deactivation of the herbicide molecule by its hydroxylation and subsequent glycosylation of the introduced hydroxyl group. Development of plants resistant to pathogens and pests The resistance of plants to various pathogens is most often a complex multigene trait.
Simultaneous transfer of several loci is difficult even by genetic engineering methods, not to mention classical selection methods. The other way is simpler. Metabolism is known to change in resistant plants when attacked by pathogens. Compounds such as H2O2, salicylic acid, phytoallexins accumulate. An increased level of these compounds contributes to the resistance of the plant in the fight against pathogens.
Here is one example proving the role of salicylic acid in the immune response of plants. Transgenic tobacco plants that contain the bacterial gene that controls the synthesis of salicylate hydrolase (this enzyme breaks down salicylic acid) were unable to mount an immune response. Therefore, a genetically engineered change in the level of salicylic acid or production in plants in response to the H2O2 pathogen may be promising for the creation of resistant transgenic plants.
In phytovirology, the phenomenon of induced cross-resistance of plants to viral infections is widely known. The essence of this phenomenon is that infection of a plant with one virus strain prevents subsequent infection of these plants with another viral strain. The molecular mechanism of viral infection suppression is still unclear. It has been shown that the introduction of individual viral genes, for example genes for capsid proteins, is sufficient for plant immunization. Thus, the gene for the envelope protein of the tobacco mosaic virus was transferred into tobacco cells and transgenic plants were obtained, in which 0.1% of all leaf proteins were represented by the viral protein. A significant part of these plants, when infected with the virus, did not show any symptoms of the disease. It is possible that the viral envelope protein synthesized in the cells prevents the viral RNA from functioning normally and forming full-fledged viral particles. It has been established that the expression of the capsid protein of tobacco mosaic virus, alfalfa mosaic virus, cucumber mosaic virus, potato X-virus in the corresponding transgenic plants (tobacco, tomatoes, potatoes, cucumbers, peppers) provides a high level of their protection from subsequent viral infection. Moreover, in the transformed plants, there was no decrease in fertility, undesirable changes in the growth and physiological characteristics of the original specimens and their offspring. It is believed that the induced resistance of plants to viruses is due to a special antiviral protein, very similar to animal interferon. It seems possible by genetic engineering to enhance the expression of the gene encoding this protein by amplifying it or substituting it for a stronger promoter.
It should be noted that the use of genetic engineering to protect plants from various pathogenic microorganisms is largely hampered by the lack of knowledge about the mechanisms of plant defense reactions. Insecticides are used to control insect pests in crop production. However, they have a harmful effect on mammals, kill beneficial insects, pollute the environment, roads, and besides, insects quickly adapt to them. More than 400 species of insects are known to be resistant to the insecticides used. Therefore, biological means of control are attracting more and more attention, providing a strict selectivity of action and the lack of adaptation of pests to the applied biopesticide.
The bacterium Bacillus thuringiensis has long been known to produce a protein that is very toxic to many insect species, while at the same time safe for mammals. The protein (delta-endotoxin, CRY protein) is produced by various strains of B. thuringiensis. The interaction of the toxin with receptors is strictly specific, which complicates the selection of the toxin-insect combination. In nature, a large number of strains of B. thuringiensis have been found, whose toxins act only on certain types of insects. Preparations of B. thuringiensis have been used for decades to control insects in fields. The safety of the toxin and its constituent proteins for humans and other mammals has been fully proven. Insertion of the gene of this protein into the plant genome makes it possible to obtain transgenic plants that are not eaten by insects.
In addition to species-specificity in terms of their effect on insects, the insertion of prokaryotic delta-toxin genes into the plant genome, even under the control of strong eukaryotic promoters, did not lead to a high level of expression. Presumably, this phenomenon arose due to the fact that these bacterial genes contain significantly more adenine and thymine nucleotide bases than plant DNA. This problem was solved by creating modified genes, where certain fragments were cut out and added from the natural gene, while the domains encoding the active parts of the delta toxin were preserved. For example, potatoes resistant to the Colorado potato beetle have been obtained using such approaches. Transgenic tobacco plants capable of synthesizing the toxin have been obtained. Such plants were insensitive to Manduca sexta caterpillars. The latter died within 3 days of contact with toxin-producing plants. Toxin formation and the resulting resistance to insects were inherited as a dominant trait.
Currently, the so-called Bt plants (from B. thuringiensis) of cotton and corn make up the bulk of the total amount of genetically modified plants of these crops that are grown in the fields of the United States.
In connection with the possibilities of genetic engineering to design entomopathogenic plants based on a toxin of microbial origin, toxins of plant origin are of even greater interest. Phytotoxins are inhibitors of protein synthesis and perform a protective function against insect pests of microorganisms and viruses. The best studied among them is ricin synthesized in castor beans: its gene has been cloned and the nucleotide sequence has been established. However, the high toxicity of ricin for mammals limits genetic engineering work with it only to industrial crops that are not used for human food and animal feed. The toxin produced by American Phytolacca is effective against viruses and is harmless to animals. Its mechanism of action is to inactivate its own ribosomes when various pathogens, including phytoviruses, enter the cells. Affected cells become necrotic, preventing the pathogen from multiplying and spreading throughout the plant. Currently, studies are underway to study the gene for this protein and transfer it to other plants.
Viral diseases are widespread among insects, so natural insect viruses, the preparations of which are called viral pesticides, can be used to control insect pests. Unlike pesticides, they have a narrow spectrum of action, do not kill beneficial insects, they are quickly destroyed in the environment and are not dangerous to plants and animals. Along with insect viruses, some fungi that infect insect pests are used as biopesticides. The currently used biopesticides are natural strains of entomopathogenic viruses and fungi, but the possibility of creating new effective biopesticides by genetic engineering methods in the future is not ruled out.
Increasing plant resistance to stressful conditions
Plants are very often exposed to various adverse environmental factors: high and low temperatures, lack of moisture, soil salinization and environmental pollution, lack or, conversely, an excess of certain minerals, etc.
There are many of these factors, and therefore the methods of protection against them are diverse - from physiological properties to structural adaptations that allow overcoming their harmful effects.
Plant resistance to a particular stress factor is the result of the influence of many different genes, so it is not necessary to talk about the complete transfer of tolerance traits from one plant species to another by genetic engineering methods. Nevertheless, there are certain opportunities for genetic engineering to improve plant resistance. This concerns work with individual genes that control the metabolic responses of plants to stress conditions, for example, proline overproduction in response to osmotic shock, salinity, synthesis of specific proteins in response to heat shock, etc. Further in-depth study of the physiological, biochemical and genetic basis The response of a plant to environmental conditions will undoubtedly allow the use of genetic engineering methods to construct resistant plants.
So far, only an indirect approach to obtaining frost-resistant plants based on genetic engineering manipulations with Pseudomonas syringae can be noted. This microorganism, coexisting with plants, contributes to their damage by early frosts. The mechanism of the phenomenon is due to the fact that the cells of the microorganism synthesize a special protein that is localized in the outer membrane and is the center of ice crystallization. It is known that the formation of ice in water depends on substances that can serve as centers of ice formation. The protein that causes the formation of ice crystals in various parts of the plant (leaves, stems, roots) is one of the main factors responsible for damage to the tissues of plants susceptible to early frosts. Numerous experiments under strictly controlled conditions have shown that sterile plants were not damaged by frosts down to -6 - 8 ° C, while in plants with the appropriate microflora, damage occurred already at temperatures of - 1.5 - 2 ° C. Mutants of these bacteria, those that lost the ability to synthesize the protein that causes the formation of ice crystals did not increase the temperature of ice formation, and plants with such microflora were resistant to frost. A strain of such bacteria, sprayed over potato tubers, competed with ordinary bacteria, which led to an increase in frost resistance of plants. It is possible that such bacteria, created using genetic engineering methods and used as a component of the external environment, will serve to combat frosts.
Increasing the efficiency of biological nitrogen fixation
The enzyme responsible for the reduction of molecular nitrogen to ammonium has been well studied. - nitrogenase. The structure of nitrogenase is the same in all nitrogen-fixing organisms. During nitrogen fixation, an indispensable physiological condition is the protection of nitrogenase from destruction by oxygen. The best studied among nitrogen fixers are rhizobia that form symbiosis with legumes and the free-living bacterium Klebsiella pneumoniae. It has been established that 17 genes, the so-called nif genes, are responsible for nitrogen fixation in these bacteria. All these genes are linked to each other and are located on the chromosome between the genes for histidine biosynthesis enzymes and the genes that determine the absorption of shikimic acid. In a rapidly growing rhizobia, nif genes exist in the form of a megaplasmid containing 200-300 thousand base pairs.
Among the nitrogen fixation genes, genes controlling the structure of nitrogenase, a protein factor involved in electron transport, and regulatory genes were identified. The regulation of nitrogen fixation genes is quite complex, so the genetically engineered transfer of the nitrogen fixing function from bacteria directly to higher plants is no longer discussed at present. As experiments have shown, even in the simplest eukaryotic organism, yeast, it was not possible to achieve the expression of nif genes, although they persisted for 50 generations.
These experiments showed that diazotrophy (nitrogen fixation) is characteristic exclusively of prokaryotic organisms, and nif genes could not overcome the barrier separating prokaryotes and eukaryotes due to their too complex structure and regulation by genes located outside the nif region. Perhaps, the transfer of nif genes with the help of Ti plasmids into chloroplasts will be more successful, since the mechanisms of gene expression in chloroplasts and in prokaryotic cells are similar. In any case, nitrogenase must be protected from the inhibitory action of oxygen. In addition, atmospheric nitrogen fixation is a very energy intensive process. It is unlikely that a plant under the influence of nif genes can change its metabolism so radically in order to create all these conditions. Although it is possible that in the future it will be possible to create a more economically operating nitrogenase complex using genetic engineering methods.
It is more realistic to use genetic engineering methods to solve the following problems: increasing the ability of rhizobia to colonize leguminous plants, increasing the efficiency of nitrogen fixation and assimilation by influencing the genetic mechanism, creating new nitrogen-fixing microorganisms by introducing nif genes into them, transferring the ability to symbiosis from leguminous plants to others .
The primary task of genetic engineering to increase the efficiency of biological nitrogen fixation is the creation of rhizobia strains with enhanced nitrogen fixation and colonizing ability. The colonization of leguminous plants by rhizobia proceeds very slowly, only a few of them give rise to nodules. This is because the place of invasion of rhizobia is only one small area between the root growth point and the root hair nearest to it, which is at the stage of formation. All other parts of the root and the developed root hairs of the plant are insensitive to colonization. In some cases, formed nodules are unable to fix nitrogen, which depends on many plant genes (at least five have been identified), in particular, on an unfavorable combination of two recessive genes.
Using traditional methods of genetics and breeding, it was possible to obtain laboratory strains of rhizobia with a higher colonizing ability. But they experience competition from local strains in the field. Increasing their competitiveness, apparently, can be done by genetic engineering methods. Increasing the efficiency of the nitrogen fixation process is possible using genetic engineering techniques based on increasing gene copies, enhancing the transcription of those genes whose products form a “bottleneck” in the nitrogen fixation cascade mechanism, by introducing stronger promoters, etc. It is important to increase the efficiency of the nitro- genase system that directly reduces molecular nitrogen to ammonia.
Improving the efficiency of photosynthesis
C4 plants are characterized by high growth rates and photosynthesis rate, they have practically no visible photorespiration. Most agricultural crops belonging to C3 plants have a high intensity of photorespiration. Photosynthesis and photorespiration are closely related processes based on the bifunctional activity of the same key enzyme, ribulose bisphosphate carboxylase (RuBPC). RuBF carboxylase can attach not only CO2, but also O2, that is, it carries out carboxylation and oxygenation reactions. The oxygenation of RuBF produces phosphoglycolate, which serves as the main substrate for photorespiration, the process of CO2 release in the light, as a result of which some photosynthetic products are lost. Low photorespiration in C4 plants is explained not by the absence of enzymes of the glycolate pathway, but by the limitation of the oxygenase reaction, as well as by the reassimilation of photorespiration CO2.
One of the tasks facing genetic engineering is to study the possibility of creating RuBPC with predominant carboxylase activity.
Obtaining plants with new properties
In recent years, scientists have been using a new approach to produce transgenic plants with "antisense RNA" (flipped or antisense RNA) that allows you to control the operation of the gene of interest. In this case, when constructing a vector, a copy of the DNA (cDNA) of the inserted gene is flipped 180°. As a result, a normal mRNA molecule and an inverted one are formed in the transgenic plant, which, due to the complementarity of normal mRNA, forms a complex with it and the encoded protein is not synthesized.
This approach was used to obtain transgenic tomato plants with improved fruit quality. The vector included cDNA of the PG gene, which controls the synthesis of polygalacturonase, an enzyme involved in the destruction of pectin, the main component of the intercellular space of plant tissues. The PG gene product is synthesized during the ripening period of tomato fruits, and an increase in its amount leads to the fact that tomatoes become softer, which significantly reduces their shelf life. Disabling this gene in transgenes made it possible to obtain tomato plants with new fruit properties, which not only lasted much longer, but the plants themselves were more resistant to fungal diseases.
The same approach can be applied to regulate the maturation of tomatoes, and in this case, the EFE (ethylene-forming enzyme) gene, the product of which is an enzyme involved in ethylene biosynthesis, is used as a target. Ethylene is a gaseous hormone, one of the functions of which is to control the process of fruit ripening.
The strategy of antisense constructs is widely used to modify gene expression. This strategy is used not only to obtain plants with new qualities, but also for basic research in plant genetics. Mention should be made of yet another direction in plant genetic engineering, which until recently was mainly used in fundamental research - to study the role of hormones in plant development. The essence of the experiments was to obtain transgenic plants with a combination of certain bacterial hormonal genes, for example, only iaaM or ipt, etc. These experiments have made a significant contribution to proving the role of auxins and cytokinins in plant differentiation.
In recent years, this approach has been used in practical breeding. It turned out that the fruits of transgenic plants with the iaaM gene under the Def gene promoter (a gene that is expressed only in fruits) are parthenocarpic, that is, formed without pollination. Parthenocarpic fruits are characterized by either a complete absence of seeds or a very small number of them, which allows solving the problem of "extra seeds", for example, in watermelon, citrus fruits, etc. Transgenic squash plants have already been obtained, which generally do not differ from the control ones, but practically do not contain seeds.
Disarmed, devoid of oncogenes Ti-plasmid, scientists are actively using to obtain mutations. This method is called T-DNA insertion mutagenesis. T-DNA, integrating into the plant genome, turns off the gene into which it is integrated, and upon loss of function, mutants can be easily selected (the phenomenon of silencing - silencing of genes). This method is also remarkable in that it allows you to immediately detect and clone the corresponding gene. Currently, many new plant mutations have been obtained in this way and the corresponding genes have been cloned. MA Ramenskaya based on T-DNA mutagenesis obtained tomato plants with nonspecific resistance to late blight. No less interesting is another aspect of the work - transgenic plants with altered decorative properties were obtained.
One example is the production of petunia plants with multicolored flowers. Next in line are blue roses with a gene that controls the synthesis of blue pigment, cloned from a delphinium.
In the universe of the strategic computer game StarCraft, the extraterrestrial Zerg race is remarkable in that it has learned to absorb the genetic material of other organisms and transform its own genes, changing and adapting to new conditions. This, at first glance, fantastic idea is much closer to the real possibilities of living organisms than it seems.
Today we know a lot about DNA: more than two million scientific publications are devoted to this double-stranded molecule. The DNA molecule can be thought of as text written using an alphabet of four letters (nucleotides). The totality of all the nucleotides that make up the chromosomes of any organism is called the genome. The human genome has approximately three billion "letters".
Separate sections of the genome are isolated genes - functional elements that are most often responsible for the synthesis of specific proteins. Humans have about 20,000 protein-coding genes. Proteins, like DNA molecules, are polymers, but they are not made up of nucleotides, but of amino acids. The "alphabet" of amino acids that make up proteins has 20 molecules. Knowing the nucleotide sequence of a gene, one can accurately determine the amino acid sequence of the protein that it encodes. The fact is that all organisms use the same (with slight variations) well-studied genetic code - the rules for matching codons (triples of nucleotides) to certain amino acids. This versatility allows genes from one organism to work in another organism and still produce the same protein.
natural engineering
One of the main methods of genetic engineering of plants uses agrobacteria and the mechanism of modification of plant genomes developed by them (see "PM" No. 10 "2005). The genes of agrobacteria living in the soil encode special proteins that can "drag" a certain DNA molecule into a plant cell, embed it into the plant genome and thereby force the plant to produce the nutrients that bacteria need.Scientists have borrowed this idea and applied it by replacing the genes that bacteria need with those that code for proteins needed in agriculture.For example, Bt toxins, which are produced by soil bacteria Bacillus thuringiensis, which are absolutely safe for mammals and poisonous for some insects, or proteins that give the plant resistance to a particular herbicide.
Gene exchange for bacteria, even unrelated ones, is a very common phenomenon. It is because of this that microbes resistant to penicillin appeared within a few years after the start of its mass use, and today the problem of antibiotic resistance has become one of the most alarming in medicine.
From viruses to organisms
Natural "genetic engineering" is carried out not only by bacteria, but also by viruses. In the genomes of many organisms, including humans, there are transposons - former viruses that have long been integrated into the host's DNA and, as a rule, without harming it, can "jump" from one place in the genome to another.
Retroviruses (such as HIV) can insert their genetic material directly into the genome of eukaryotic cells (such as human cells). Adenoviruses do not embed their genetic information into the genomes of animals and plants: their genes can turn on and work without it. These and other viruses are actively used in gene therapy to treat a wide range of hereditary diseases.
Thus, natural genetic engineering is very widely used in nature and plays a huge role in the adaptation of organisms to the environment. More importantly, all living organisms are constantly undergoing genetic changes as a result of random mutations. An important conclusion follows from this: in fact, every organism (except for clones) is unique and genetically modified compared to its ancestors. He has both new mutations and new combinations of previously existing gene variants - in the genome of any child, dozens of genetic variants are found that none of the parents had. In addition to the emergence of new mutations, in the course of sexual reproduction in each generation, a new combination of genetic variants already existing in the parents arises.
Tested in experiments
Today, the safety of food products containing genetically modified organisms (GMOs) is being actively discussed. For the products of genetic engineering carried out by man, the term "genetically modified organisms" is much better suited, since genetic engineering allows you to accelerate the processes of genetic changes that occur independently in nature and direct them in the right direction for a person. However, there are no significant differences between the mechanisms of genetic modernization and natural processes of genetic modification, so it can be reasonably considered that the production of GM foodstuffs does not carry additional risks.
However, like any scientific hypothesis, the safety of GMOs needed experimental verification. Contrary to the numerous statements of opponents of GMOs, this issue has been very, very carefully studied for more than a dozen years. This year in the magazine Critical reviews in biotechnology published a review of almost 1800 scientific papers on the study of the safety of GMOs over the past ten years. Only three studies raised suspicions about the negative impact of three specific GM varieties, but these suspicions were not justified, in two more cases the potential allergenicity of GM varieties was established. The only confirmed case involved the Brazil nut gene being inserted into a GM soybean variety. The standard test in such cases for the reaction of the blood serum of people with allergies to the protein of a new GM variety showed the existence of a danger, and the developers refused to promote the variety on the market.
In addition, it is worth mentioning separately the review of 2012 published in the journal Food and Chemical Toxicology, which included 12 studies on the safety of GMOs in food in several (two to five) generations of animals and 12 animal studies of long-term (from three months to two years) consumption of GMOs in food. The review authors concluded that there were no negative effects of GMOs (compared to non-modernized counterparts).
Scandalous revelations
Curiosities arise around some works that allegedly show the harm of certain GM plant varieties. A typical example that opponents of GMOs are very fond of citing is the sensational publication of the French researcher Séralini in the journal Food and Chemical Toxicology, who claimed that GM corn causes cancer and increased mortality in rats. In the scientific community, Seralini's work caused heated discussions, but not because the researcher received and published some unique data. The reason was that, from a scientific point of view, the work was done extremely carelessly and contained gross errors that were noticeable at first sight.
Nevertheless, the photographs of rats with large tumors presented by Séralini made a huge impression on the public. Despite the fact that his article could not withstand objective criticism and was withdrawn from the journal, it continues to be quoted by opponents of GMOs, who are clearly not interested in the scientific side of the issue, and photographs of sick rats are still shown from the screens.
The scientific level of discussion of the potential dangers of GMOs in the media and in society as a whole is striking in its naivety. On the shelves of stores you can find starch, salt and even “non-GMO” water. GMOs are constantly confused with preservatives, pesticides, synthetic fertilizers and food additives, to which genetic engineering is not directly related. From the real problems of food safety, such discussions lead to the realm of speculation and substitution of concepts.
Dangers - real and not
However, neither this article nor other scientific papers attempt to prove that GMOs are “absolutely safe.” In fact, no food is absolutely safe, because even Paracelsus said the famous phrase: “Everything is poison, and nothing is devoid of poison; one dose makes the poison invisible. Even ordinary potatoes can cause allergies, and green ones contain toxic alkaloids - solanines.
Can the work of existing plant genes somehow change as a result of the insertion of a new gene? Yes, it can, but no organism is immune from changes in the work of genes. Can genetic engineering produce a new plant variety that will spread beyond the agricultural land and somehow affect the ecosystem? Theoretically, this is possible, but it happens everywhere in nature: new species appear, ecosystems change, some species die out, others take their place. However, there is no reason to believe that genetic engineering carries additional risks to the environment or to the health of humans or animals. But these risks are constantly trumpeted in the media. Why?
The GMO market is largely monopolized. Among the giants, Monsanto is in first place. Of course, the big producers of GM seeds and technologies are interested in profit, they have their own interests and their own lobby. But they do not earn money “out of thin air”, but by offering humanity progressive agricultural technologies, for which producers vote in the most convincing way - in dollars, pesos, yuan, etc.
The main producers and suppliers of "organic" products grown using outdated technologies and, therefore, more expensive (but not better) are also not small farmers at all, but the same large companies with multibillion-dollar turnovers. In the US alone, the organic food market was worth $31 billion in 2012. This is a serious business, and since organic products do not have any advantages over GMOs, but are more expensive to produce, they cannot compete with GM varieties using market methods. So we have to inspire gullible consumers through the media with an unfounded fear of the mythical "scorpion genes", which creates a demand for expensive and low-tech "organic products". In addition, anti-GMOs describing the terrible dangers of genetically modified varieties that produce protein B. thuringiensis, they usually forget to mention that preparations based on such crops or proteins isolated from them are allowed in “organic farming” (and are widely used). As well as natural manure, which can be a source of a bunch of pathogenic bacteria and other natural muck.
A bit of politics
Today, genetic engineering is one of the most studied technologies in terms of safety. It allows you to create better food, reduce the amount of pesticides used in the fields and protect the environment (yes, to protect: more insects and birds live on fields sown with Bt varieties than on “normal” ones, which have to be regularly treated with insecticides) .
But there is another reason for the "fight" against GMOs - exclusively political. Countries far behind in biotechnology are trying to find an excuse to keep cheaper products from other countries out of their markets. However, such protection of domestic producers from foreign products makes sense only if it helps to buy time to develop their own technologies to a competitive state. If this is not done, there is a serious risk of lagging behind the world scientific and technological level. Forever.
SCIENTIFIC LIBRARY - ABSTRACTS - Gene modification
Gene modification
Geneticists and breeders discuss the most complex problems of plant and animal breeding, the use of genetic technologies in medicine, and the safety of genetically modified products.
1. Genetic engineering
Genetic engineering is a branch of molecular genetics associated with the targeted creation of new combinations of genetic material. The basis of applied genetic engineering is the theory of the gene. The created genetic material is capable of reproducing in the host cell and synthesizing end products of metabolism.
Genetic engineering originated in 1972 at Stanford University in the USA. Then the laboratory of P. Berg received the first recombinant (hybrid) DNA or (recDNA). It combined DNA fragments of the lambda phage, Escherichia coli and the monkey virus SV40.
The structure of recombinant DNA. Hybrid DNA has the form of a ring. It contains a gene (or genes) and a vector. A vector is a DNA fragment that ensures the reproduction of hybrid DNA and the synthesis of end products of the genetic system - proteins. Most of the vectors were obtained on the basis of the lambda phage, from plasmids, SV40 viruses, polyoma, yeast, and other bacteria.
Protein synthesis occurs in the host cell. The most commonly used host cell is Escherichia coli, but other bacteria, yeast, animal or plant cells are also used. The host-vector system cannot be arbitrary: the vector is tailored to the host cell. The choice of vector depends on the species specificity and the objectives of the study.
Two enzymes are of key importance in the construction of hybrid DNA. The first - restriction enzyme - cuts the DNA molecule into fragments in strictly defined places. And the second - DNA ligases - sew DNA fragments into a single whole. Only after the isolation of such enzymes did the creation of artificial genetic structures become a technically feasible task.
Stages of gene synthesis. The genes to be cloned can be obtained as fragments by mechanical or restrictase fragmentation of total DNA. But structural genes, as a rule, have to be either synthesized chemically and biologically or obtained in the form of a DNA copy of messenger RNA corresponding to the chosen gene. Structural genes contain only an encoded record of the final product (protein, RNA), and are completely devoid of regulatory regions. And so these genes are not able to function in the host cell.
Upon receipt of recDNA, several structures are most often formed, of which only one is needed. Therefore, the mandatory step is the selection and molecular cloning of recDNA introduced by transformation into the host cell.
There are 3 ways of recDNA selection: genetic, immunochemical and hybridization with labeled DNA and RNA.
As a result of the intensive development of genetic engineering methods, clones of many genes have been obtained: ribosomal, transport and 5S RNA, histones, mouse, rabbit, human globin, collagen, ovalbumin, human insulin and other peptide hormones, human interferon, etc. This made it possible to create strains of bacteria that produce many biologically active substances used in medicine, agriculture and the microbiological industry.
On the basis of genetic engineering, a branch of the pharmaceutical industry called the "DNA industry" arose. It is one of the modern branches of biotechnology.
There is no doubt that the search for geneticists promises a person getting rid of many ailments. Already, genetic engineering is beginning to be actively used in oncology, drugs are being created that are targeted against a specific tumor. Scientists have identified genes that predispose to the development of diabetes, which means that new prospects have appeared in the treatment of this serious illness. Human insulin (humulin) obtained by means of recDNA is approved for therapeutic use. In addition, based on numerous mutants for individual genes obtained during their study, highly effective test systems have been created to detect the genetic activity of environmental factors, including the detection of carcinogenic compounds.
In a short time, genetic engineering has had a huge impact on the development of molecular genetic methods and has made it possible to make significant progress along the path of understanding the structure and functioning of the genetic apparatus. Genetic engineering has great prospects in the treatment of hereditary diseases, of which about 2000 have been registered today. Genetic engineering is designed to help correct the mistakes of nature.
On the other hand, genetic technologies have created completely new problems related to the possibility of cloning living beings, including humans. The global scientific community recognizes that it is technically possible to clone an identical human individual. But the question of whether humanity needs such attempts remains open. It has been proven that in 99 percent of cases there is a risk of congenital deformities - which means that such experiments on a person are unacceptable.
However, new genetic technologies based on transgenesis and cloning play an important role in creating highly productive plant varieties and animal breeds. At the same time, problems of both genetic safety and moral and legal ones come to the fore.
In Russia, all research on cloning is carried out only on animals. Furious discussions are going on all over the world - including in Russia - around another product of modern science: genetically modified foods.
2. Is gene modification safe?
The creators of genetically modified products claim that they are completely safe. Proponents of their widespread use are confident that many years of research have proven the safety of such products. Opponents are convinced otherwise.
So far, these products have not been proven safe for humans. Many types of genetically modified products are prohibited for use in the last stages of the experiment as strong allergens.
Are the skeptics right who say that transgenic products are dangerous? Or maybe they will become our food in the 21st century?
About 30 years ago, the first experiments on the genetic modification of plants were made. For example, you can take one gene from one animal or plant and insert it into another animal or plant. In this way, for example, pesticide-resistant potatoes can be obtained.
Genetically modified foods are not only created, but they are actively eaten.
Traditional breeding involves crossing within the same species. Even the tomato has been improved by breeding. But, during selection, there is an exchange between individuals of the same species. And genetic engineering allows you to make new DNA and manipulate it. For example, if the firefly gene is inserted into the DNA of tobacco, then the tobacco flower begins to glow if it needs watering. It is not possible to achieve this by selection methods!
The protesters most of all pay attention to the negative processes of this technique. But after all, no one argues with the fact that genetically modified products need testing!
Defenders of the biotechnology industry argue that all processes related to genetically modified products are under tight control.
The analysis of ordinary and transgenic plants is carried out. Scientists must prove to inspectors that foodstuffs do not differ in quality.
Product verification goes through the following steps:
1. Comparison of the structure and chemical composition of common and transgenic plants.
2. Evidence is required that the consumption of a new product does not harm human health.
Transgenic soy (has resistance to herbicides) is included in the products that we eat in recent years.
Is the new protein toxic? For several years, the protein was tested for toxicity. Mice were fed doses 1000 times higher than the doses that a person consumes. Scientists claim that nothing harmful to the human body has been identified.
How are new proteins digested? Proteins created artificially are immersed in a solution that has an environment similar in composition to the intestines. The faster the product is digested, the better.
Experiments have shown that the new protein is not an allergen. There are other ways to test the created protein. If it fails the test, it is destroyed. However, the transgenic soybean protein successfully passed the test! 1800 analyzes were carried out, which showed that everything is in order with soybeans.
The test system is working. You just need to follow the methodology, scientists say.
But skeptics believe that science still knows too little to claim that "everything is under control." Living organisms are so complex that it is almost impossible to predict their behavior.
However, traditional breeding methods are not always safe. On the contrary, in genetic engineering, the ways of introducing a gene are precisely known. Again, skeptics are sure that genetic engineering, using new methods, risks causing irreparable harm to nature. Their opponents say that selection is dangerous as well. it deals not with one, but with several genes! Therefore, the result of selection is even more unpredictable!
The worst thing is that 30 years ago they experimented with genes without understanding what they were doing!
Resistance to genetically modified products in Europe is stronger than anywhere else in the world. Recently, the introduction of transgenic products has been very difficult: in England, about 2000 such products were introduced, and now there are less than 100 left!
3. Examples of gene modification
Public organizations in Europe are calling for the destruction of transgenic plants. Strange plants are obtained by implanting animal genes into them. Environmentalists are against these technologies, the public is arrogant and contemptuous of genetically modified products.
3.1 Enlargement of the corn cob
Mexico has poor soils, and therefore very poor corn crops. Scientists have been tasked with increasing the size of the corn cob. As a result of the research, a gene was implanted in corn that neutralizes aluminum salts and dissolves phosphates, which allowed the plant to fully develop on the proposed soils.
The harvest promised to be 2 times larger, but the government, under pressure from environmental organizations, banned these studies. Environmentalists ignore the results of the experiment. Opponents of genetic engineering believe that such experiments are harmful to the environment, dangerous to health and ultimately lead to an ecological disaster. After all, no one can guarantee that these techniques will not lead to the emergence of new insects and weeds!
3.2 Cotton protection
University of Arizona. Scientists are working to increase the yield of cotton. The plant is suffering from an invasion of the pink box worm. If the pest population is large, then cotton yields are falling rapidly!
It is required to introduce into cotton a gene that will kill the box worm. For the past 40 years, spraying of plants with chemicals has been used to kill insects. Both people and animals suffered. They tried to implant a bacterium gene into cotton. A protein appeared in the leaves of the plant, which is poisonous to the worm. Thus, the need to protect the plant with chemicals is eliminated!
As a result, hundreds of hectares of poisonous plants were obtained, which themselves protect themselves from harmful insects. Again, time will pass, and the pests will get used to it, develop immunity!
But not only beetles - pests inspire fear! Ecologists are afraid that especially resistant weeds will appear, and, therefore, there will be no salvation from weeds resistant to chemicals. After all, bees can carry pollen for several kilometers, and these plants will fill the entire district. However, there is evidence that pollination no longer occurs at a distance of 15 m. But even if the pollen of a modified plant overcomes the distance, then it must cross with its own species. Super-survivability is not so easy to maintain ...
3.3 Rice with vitamin A
Asia. 100 million children do not receive vitamin A, which is necessary for full vision. The fact is that the main food of the poorest segments of the population is rice. Children go blind from lack of vitamin A!
It is a noble task to grow rice immediately with vitamin A and sow it in fields in backward countries. How is this possible? Narcissus is a poisonous plant. It is necessary to take 2 genes from it and introduce it into rice, which in this case will contain vitamin “A”!
4. Horrors of genetic modification
Human liver gene added to rice! Scientists have begun adding human genes to rice in an attempt to take genetically modified foods to the next level.
Researchers have introduced into rice a gene derived from the human liver, which produces an enzyme that promotes the breakdown of harmful chemical elements in the human body. They hope that an enzyme - CYP2B6 - will do the same to herbicides and pollutants when mixed with rice.
However, opponents of genetically modified foods say that the use of human genes will scare off consumers who are disgusted by the idea of cannibalism and scientists taking on the functions of a god. Sue Meyer of UK-based GeneWatch says: "I don't think anyone would want to buy this rice." "People have already expressed their disgust at the use of human genes and their dismay at the feeling that the biotechnology industry is not listening to them. This will further shake their confidence."
Genetic modification of crops usually uses genes obtained from bacteria. They are resistant to only one type of herbicide, which means that farmers can treat their fields as often as they like for pest control, but only one type of chemical. The goal of adding a human gene to rice is to create a plant that is resistant to several types of herbicides.
Researchers at the National Institute of Agricultural Biological Sciences in Tsukuba in Japan have found that a new type of rice could be resistant to 14 different types of herbicides. Professor Richard Meylan, who has done similar research at the Purdue Institute in Indiana, says that such rice can be grown on soil saturated with industrial pollution. He used rabbit genes in his research, but says he sees no reason why human genes should not be used. He says the talk of "Frankenstein food" is nonsense, and adds, "I don't think ethical considerations have anything to do with the use of human genes in genetic engineering to grow food."
Rice production around the world is falling, and there is a race to find ways to increase rice yields, as well as new varieties of rice that are resistant to viruses, low in allergens and protein.
However, in the Institute of Science in the society of opponents of genetic modification, they say that the CYP2B6 enzyme can hit a person, leading to the creation of new viruses or cancers.
They add: "Gene-modifying advocates and major rice-producing countries are researching and promoting GM rice with no regard for safety or long-term perspective."
Conclusion
Skeptics are not sure that genetic technologies will solve social problems. Dreams of an equal distribution of food throughout the world are a utopia.
Resistance to genetically modified products in Europe is stronger than anywhere else in the world. The creators of genetically modified products claim that they are completely safe. In turn, opponents of genetic modification consider it a "Pandora's box" with unpredictable consequences.
Obviously, in the coming decades, genetics will still present many surprises to mankind, give rise to many sensations - imaginary and real, disputes and even scandals will rage around it. Society easily hears those people who are afraid of everything new, but the danger from mobile phones is no less!
The main thing is that all this fuss should not interfere too much with the serious work of scientists in one of the most interesting and promising scientific areas.
Terminological dictionary
Genetic Engineering- the practice of purposefully changing the genetic programs of germ cells in order to give the original forms of organisms new properties or create fundamentally new forms of organisms. The main method of genetic engineering consists in extracting a gene or a group of genes from the cells of an organism, combining them with certain nucleic acid molecules and introducing the resulting hybrid molecules into the cells of another organism.
Biological protection- in genetic engineering - the creation and use of a combination of biological material that is safe for humans and environmental objects, the properties of which exclude the undesirable survival of genetically modified organisms in the environment and / or the transfer of genetic information to them
Biotechnology- in a broad sense - a scientific discipline and a field of practice bordering between biology and technology, studying the ways and methods of changing the natural environment around a person in accordance with his needs.
Biotechnology- in a narrow sense - a set of methods and techniques for obtaining products and phenomena useful to humans with the help of biological agents. Biotechnology includes genetic, cellular and environmental engineering
Release of genetically modified organisms into the environment- action or inaction resulting in the introduction of genetically modified organisms into the environment.
Genetic engineering activities- activities carried out using genetic engineering methods and genetically modified organisms.
Genetically engineered organism- an organism or several organisms, any non-cellular, unicellular or multicellular formation: - capable of reproduction or transmission of hereditary genetic material; - different from natural organisms; - obtained using genetic engineering methods; and - containing genetically engineered material.
Gene diagnostics- in genetic engineering - a set of methods for detecting changes in the structure of the genome.
closed system- in genetic engineering- a system for the implementation of genetic engineering activities, in which genetic modifications are introduced into the body or genetically modified organisms, processed, cultivated, stored, used, transported, destroyed or buried under the conditions of the existence of physical, chemical and biological barriers or their combinations, preventing contact of genetically modified organisms with the population and the environment.
open system- in genetic engineering- a system for the implementation of genetic engineering activities, involving the contact of genetically modified organisms with the population and the environment when they are intentionally released into the environment, used for medical purposes, exported and imported, and transferred technologies.
transgenic organisms- animals, plants, microorganisms, viruses whose genetic program has been modified using genetic engineering methods.
Physical protection- in genetic engineering- creation and use of special technical means and techniques that prevent the release of genetically modified organisms into the environment and / or the transfer of genetic information to them.
Literature
1. Maniatis T., Methods of genetic engineering, M., 1984;
2. Genetic engineering Source #"#">#"#">Rubricon
Genetically modified organism - an organism or several organisms, any non-cellular, unicellular or multicellular formation: - capable of reproduction or transmission of hereditary genetic material; - different from natural organisms; - obtained using genetic engineering methods; and - containing genetically engineered material.
Phages, same as bacteriophages. ... phage (from the Greek Phagos - eater) part of compound words, corresponding in meaning to the words "eating", "absorbing" (for example, bacteriophage).
Biotechnology is a set of methods and techniques for obtaining products and phenomena useful to humans with the help of biological agents. Biotechnology includes genetic, cellular and ecological engineering.
Genetics have bred soybeans to prevent hair loss. In Japan, a genetically modified variety of soybeans has been developed that stimulates hair growth and prevents hair loss from chemotherapy. If the safety of the new product is confirmed, then in order to save yourself from baldness, you just need to eat these beans periodically, said Professor Massaki Yoshikawa, head of the Kyoto University research group, on Wednesday. The miraculous property of the grain crop was given by a genetically introduced component (novokinin), which has an antihypertensive effect. It was derived from the amino acid composition of egg white. According to scientists, this component promotes hair growth by dilating blood vessels and normalizing blood circulation. The effectiveness of beans has been confirmed in experiments on mice that were shaved and then fed modified beans at the rate of one thousandth of a milligram of an antihypertensive agent per gram of body weight. Coat recovery was reported to be accelerated, and after increasing the dose, mice stopped losing hair even as a result of chemotherapy. Experts say that their beans can also be used as a common cure for high blood pressure. 13 April 2005
genetic modification ( GM) - a change in the genome of a living organism using genetic engineering technology, by introducing one or more genes taken from one donor organism to another. After such an introduction (transfer), the resulting plant will already be called genetically modified, or transgenic. In contrast to traditional breeding, the original genome of the plant is almost not affected, and the plant acquires new traits that it did not possess before. Such signs (characteristics, properties) include: resistance to various environmental factors (to frost, drought, moisture, etc.), to diseases, to pests, improved growth properties, resistance to herbicides, pesticides. Finally, scientists can change the nutritional properties of plants: taste, aroma, calorie content, storage time. Using genetic engineering, it is possible to increase crop yields, which is very important, given that the world population is growing every year and the number of hungry people in developing countries is increasing.
With traditional breeding, a new variety can be obtained only within the same species. For example, you can breed a completely new variety of rice by crossing different varieties of rice with each other. In this case, a hybrid combination is obtained, from which the breeder then selects only the forms of interest to him.
Since hybridization is carried out between individual plants, it is almost impossible to develop a variety that would have the characteristics of interest to us, which will be inherited by the following generations. It takes a lot of time to solve such a problem. If it is necessary to develop a new variety of wheat and for this variety to acquire some characteristics of rice, then traditional breeding is powerless here. Came to the rescue, when using it, it is possible to transfer certain characteristics (properties) to the experimental plant, and all this will be carried out at the level DNA, individual genes. In a similar way, for example, wheat can be transferred gene frost resistance.
The method of genetic modification allows, at least theoretically, to isolate individual genes that are responsible for certain properties of living organisms and instill them in completely different organisms, while significantly shortening the time for creating a new species. That is why many breeders and scientists around the world use this technology when breeding new varieties. Pesticide (herbicide), pest and disease resistant commercial crop varieties have now been developed. And also, varieties with improved taste, resistant to drought and frost were obtained.
Polymeria - the interaction of non-allelic multiple genes that unidirectionally affect the development of the same trait; the degree of manifestation of a trait depends on the number of genes. Polymeric genes are denoted by the same letters, and alleles of the same locus have the same subscript.
The polymer interaction of non-allelic genes can be cumulative and non-cumulative. With cumulative (accumulative) polymerization, the degree of manifestation of a trait depends on the total action of several genes. The more dominant alleles of genes, the more pronounced this or that trait. Splitting in F2 according to the phenotype during dihybrid crossing occurs in a ratio of 1: 4: 6: 4: 1, and in general corresponds to the third, fifth (during dihybrid crossing), seventh (during trihybrid crossing), etc. lines in Pascal's triangle.
With non-cumulative polymerism, the trait manifests itself in the presence of at least one of the dominant alleles of polymeric genes. The number of dominant alleles does not affect the severity of the trait. Splitting in F2 by phenotype in dihybrid crossing - 15:1.
An example of polymerism is the inheritance of skin color in humans, which depends (in a first approximation) on four genes with a cumulative effect.
Modifier gene
A gene that does not have its own expression in the phenotype, but has an amplifying or weakening effect on the expression of other genes (respectively, an intensifier gene
20. Chromosomal theory and the history of its creation.
21.Mechanisms of sex inheritance. Influence of factors of the internal and external environment on the development of sex characteristics.
22. Inheritance of sex-linked traits.
All bisexual organisms have two types of chromosomes. The first type is autosomes (non-sex chromosomes). They are the same in female and male organisms. The second type is the sex chromosomes, according to which there are differences in organisms by sex: females have 2 identical XX chromosomes, males have XY. This type of sex is called homogametic. Typical for mammals, fish, insects. The second type of sex is heterogametic, females are XY, males are XX. The sex chromosomes differ in size. In most organisms, many genes are located on the X chromosome, and single genes are localized on the Y chromosome. Only in fish, the Y chromosome is relatively richer in genes. If the genes are localized on the X chromosome, and the Y chromosome is genetically internal, then this type of trait inheritance is called sex-linked inheritance. If the genes are present on only one chromosome, and the second is genetically interna, then such organisms are called genizygous.
23. Linked inheritance and crossing over
Since most organisms have many (several thousand) genes, and a limited number of chromosomes, several genes are located simultaneously on one chromosome. Genes that are part of the same chromosome are called linked and form a linkage group. They are inherited as a whole, since this is determined by the behavior of the chromosome in meiosis. In this case, splitting according to linked traits does not obey the law of independent inheritance. If the genes are located close to each other, then they always remain in the original combinations.
For example, AB / ab x ab / ab -> 1 Ab / ab: 1 ab / ab.
This is a case of so-called full coupling, which is not often observed. Much more common are situations where genes are located at some distance from each other. In such a case of partial linkage, they can separate by a process called crossing over. This is another kind of genetic recombination. Crossing over occurs in the prophase of the first meiotic division at the time of chromosome conjugation. At this time, chromatids of homologous chromosomes exchange fragments of hereditary material, resulting in new combinations of genes.
For example, AB / ab x ab / ab → AB / ab: ab / ab: Ab / ab: aB
The number of recombinant (or crossover) classes is always less than non-recombinant, and the ratio of the two classes within each group is always 1:1. The crossover value, calculated as the percentage of recombinants to the total number of offspring, is an indicator of the distance between genes and is used for chromosome mapping - the location of genes on a chromosome map in a strictly defined order and at fixed distances. These distances have the additivity property, which is as follows. If there are three genes arranged in the order A-B-C, then AC = AB + BC. Such additivity unambiguously indicates the linear arrangement of genes in chromosomes.
If crossing over between a large number of genes is considered, then the picture is much more complex - individual crossing over acts interact with each other. Such mutual influence of crossing-over acts is called interference.
