Mutations and types of mutations. The main causes of gene mutations at the present stage. By way of occurrence

As part of the formal classification, there are:

Genomic mutations - a change in the number of chromosomes;
chromosomal mutations - rearrangement of the structure of individual chromosomes;
gene mutations - and / or sequences of constituent parts of genes (nucleotides) in the DNA structure, the consequence of which is a change in the quantity and quality of the corresponding protein products.

Gene mutations occur by substitution, deletion (loss), translocation (movement), duplication (doubling), inversion (change) of nucleotides within individual genes. In that case when we are talking about transformations within a single nucleotide, they use the term point mutation.

Such nucleotide transformations cause the appearance of three mutant codes:

With an altered meaning (missense mutations), when in the polypeptide encoded by this gene, one amino acid is replaced by another;
with unchanged meaning (neutral mutations) - the replacement of nucleotides is not accompanied by the replacement of amino acids and does not have a noticeable effect on the structure or function of the corresponding protein;
meaningless (nonsense mutations), which can cause polypeptide chain termination and have the greatest damaging effect.

Mutations in different parts of the gene

If we consider a gene from the position of structural and functional organization, then the dropouts, insertions, substitutions and movements of nucleotides occurring in it can be divided into two groups:

1. mutations in the regulatory regions of the gene (in the promoter part and in the polyadenylation site), which cause quantitative changes in the corresponding products and manifest themselves clinically depending on the limiting level of proteins, but their function is still preserved;

2. mutations in the coding regions of the gene:
in exons - cause premature termination of protein synthesis;
in introns - they can generate new splicing sites, which, as a result, replace the original (normal) ones;
at splicing sites (at the junction of exons and introns) - lead to the translation of meaningless proteins.

To eliminate the consequences of this kind of damage, there are special reparation mechanisms. The essence of which is to remove the erroneous section of DNA, and then the original one is restored at this place. Only in the event that the repair mechanism has not worked or has not coped with the damage does a mutation occur.

The hereditary information of a cell is recorded in the form of a DNA nucleotide sequence. There are mechanisms to protect DNA from external influences in order to avoid damage to genetic information, however, such violations occur regularly, they are called mutations.

Mutations- changes that have arisen in the genetic information of the cell, these changes can have a different scale and are divided into types.

Mutation types

Genomic mutations- changes concerning the number of whole chromosomes in the genome.

Chromosomal mutations- changes relating to regions within the same chromosome.

Gene mutations- changes occurring within a single gene.

As a result of genomic mutations, there is a change in the number of chromosomes within the genome. This is due to a malfunction of the division spindle, thus, homologous chromosomes do not diverge to different poles of the cell.

As a result, one cell acquires twice as many chromosomes as it should (Fig. 1):

Rice. 1. Genomic mutation

The haploid set of chromosomes remains the same, only the number of sets of homologous chromosomes (2n) changes.

In nature, such mutations are often fixed in the offspring; they occur most often in plants, as well as in fungi and algae (Fig. 2).

Rice. 2. Higher plants, mushrooms, algae

Such organisms are called polyploid, polyploid plants can contain from three to one hundred haploid sets. Unlike most mutations, polyploidy most often benefits the body, polyploid individuals are larger than normal ones. Many cultivars of plants are polyploid (Fig. 3).

Rice. 3. Polyploid crop plants

A person can artificially induce polyploidy by treating plants with colchicine (Fig. 4).

Rice. 4. Colchicine

Colchicine destroys the spindle fibers and leads to the formation of polyploid genomes.

Sometimes during division, non-disjunction in meiosis may occur not for all, but only for some chromosomes, such mutations are called aneuploid. For example, the mutation trisomy 21 is typical for a person: in this case, the twenty-first pair of chromosomes does not diverge, as a result, the child receives not two twenty-first chromosomes, but three. This leads to the development of Down syndrome (Fig. 5), as a result of which the child is mentally and physically handicapped and sterile.

Rice. 5. Down syndrome

A variety of genomic mutations is also the division of one chromosome into two and the fusion of two chromosomes into one.

Chromosomal mutations are divided into types:

- deletion- loss of a chromosome segment (Fig. 6).

Rice. 6. Deletion

- duplication- duplication of some part of the chromosomes (Fig. 7).

Rice. 7. Duplication

- inversion- rotation of a chromosome region by 180 0, as a result of which the genes in this region are located in a reverse sequence compared to the norm (Fig. 8).

Rice. 8. Inversion

- translocation- moving any part of the chromosome to another place (Fig. 9).

Rice. 9. Translocation

With deletions and duplications, the total amount of genetic material changes, the degree of phenotypic manifestation of these mutations depends on the size of the altered areas, as well as on how important genes got into these areas.

During inversions and translocations, the amount of genetic material does not change, only its location changes. Such mutations are evolutionarily necessary, since mutants often can no longer interbreed with the original individuals.

Bibliography

1. Mamontov S.G., Zakharov V.B., Agafonova I.B., Sonin N.I. Biology, 11th grade. General biology. Profile level. - 5th edition, stereotypical. - Bustard, 2010.
2. Belyaev D.K. General biology. A basic level of. - 11th edition, stereotypical. - M.: Education, 2012.
3. Pasechnik V.V., Kamensky A.A., Kriksunov E.A. General biology, grades 10-11. - M.: Bustard, 2005.
4. Agafonova I.B., Zakharova E.T., Sivoglazov V.I. Biology 10-11 class. General biology. A basic level of. - 6th ed., add. - Bustard, 2010.

1. Internet portal "genetics.prep74.ru" ()
2. Internet portal "shporiforall.ru" ()
3. Internet portal "licey.net" ()

Homework

1. Where are genome mutations most common?
2. What are polyploid organisms?
3. What are the types of chromosomal mutations?

Mutations are changes in the DNA of a cell. Arise under the influence of ultraviolet, radiation (X-rays), etc. They are inherited, serve as material for natural selection. Differences from modifications

Gene mutations- a change in the structure of one gene. This is a change in the sequence of nucleotides: dropout, insertion, replacement, etc. For example, replacing A with T. Causes - violations during doubling (replication) of DNA. Examples: sickle cell anemia, phenylketonuria.

Chromosomal mutations– change in the structure of chromosomes: loss of a segment, doubling of a segment, rotation of a segment by 180 degrees, transfer of a segment to another (non-homologous) chromosome, etc. Causes - violations during crossing over. Example: cat cry syndrome.

Genomic mutations- change in the number of chromosomes. Causes - violations in the divergence of chromosomes.

• polyploidy– multiple changes (several times, for example, 12 → 24). It does not occur in animals, in plants it leads to an increase in size.
• Aneuploidy- changes on one or two chromosomes. For example, one extra twenty-first chromosome leads to Down syndrome (while the total number of chromosomes is 47).

Cytoplasmic mutations- changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because. mitochondria and plastids from spermatozoa do not enter the zygote. An example in plants is variegation.

Somatic- mutations in somatic cells (cells of the body; there may be four of the above types). During sexual reproduction, they are not inherited. They are transmitted during vegetative propagation in plants, during budding and fragmentation in coelenterates (in hydra).

induced mutagenesis.

Experimental obtaining of mutations in plants and microorganisms and their use in breeding

in effective ways obtaining source material are methods induced mutagenesis– artificial obtaining of mutations. Induced mutagenesis makes it possible to obtain new alleles that cannot be found in nature. For example, highly productive strains of microorganisms (producers of antibiotics), dwarf varieties of plants with increased precocity, etc. have been obtained in this way. Experimentally obtained mutations in plants and microorganisms are used as material for artificial selection. In this way, highly productive strains of microorganisms (producers of antibiotics), dwarf varieties of plants with increased precocity, etc. have been obtained.

To obtain induced mutations in plants, physical mutagens (gamma radiation, X-ray and ultraviolet radiation) and specially created chemical supermutagens (for example, N-methyl-N-nitrosourea) are used.

The dose of mutagens is selected in such a way that no more than 30 ... 50% of the treated objects die. For example, when using ionizing radiation, such a critical dose ranges from 1...3 to 10...15 and even 50...100 kiloroentgens. When using chemical mutagens, their aqueous solutions with a concentration of 0.01 ... 0.2% are used; processing time - from 6 to 24 hours or more.

Processing is subjected to pollen, seeds, seedlings, buds, cuttings, bulbs, tubers and other parts of plants. Plants grown from treated seeds (buds, cuttings, etc.) are marked with the symbol M 1 (first mutant generation). AT M 1 selection is difficult, since most of the mutations are recessive and do not appear in the phenotype. In addition, along with mutations, non-inherited changes are often encountered: phenocopies, terates, morphoses.

Therefore, the isolation of mutations begins at M 2 (second mutant generation), when at least some of the recessive mutations are manifested, and the probability of preserving non-hereditary changes is reduced. Usually, selection continues for 2–3 generations, although in some cases it takes up to 5–7 generations to cull non-inherited changes (such non-hereditary changes that persist for several generations are called long-term modifications).

The resulting mutant forms either directly give rise to a new variety (for example, dwarf tomatoes with yellow or orange fruits) or are used in further breeding work.

However, the use of induced mutations in breeding is still limited, since mutations lead to the destruction of historically established genetic complexes. In animals, mutations almost always lead to reduced viability and/or infertility. A few exceptions include the silkworm, with which intensive breeding work was carried out using auto- and allopolyploids (B.L. Astaurov, V.A. Strunnikov).

Somatic mutations. As a result of induced mutagenesis, partially mutant plants (chimeric organisms) are often obtained. In this case, one speaks of somatic (kidney) mutations. Many varieties of fruit plants, grapes, and potatoes are somatic mutants. These varieties retain their properties if they are reproduced vegetatively, for example, by grafting buds (cuttings) treated with mutagens into the crown of non-mutant plants; in this way, for example, seedless oranges are propagated.

The tasks of agricultural production include a worldwide increase in the production of grain, industrial, vegetable and fruit crops.
The solution of these problems is possible in the presence of new promising, intensive varieties of various crops. Obtaining new varieties of intensive type is possible, in particular, with the help of chemical mutagens.
The impact of mutagenic factors on the original forms increases the frequency of mutations and allows you to create the richest breeding material that has a complex of valuable economic traits and properties.
Thus, in many scientific institutions in our country and abroad, new varieties were obtained as a result of the use of physical and chemical mutagens. These are varieties of spring and winter wheat, characterized by increased productivity, resistance to many diseases and other useful properties. Tomato varieties have also been obtained, which are distinguished by high productivity, high taste and technological qualities, suitable for mechanized harvesting.
Recently, intensive studies are also being conducted on induced mutagenesis in industrial fish farming - carp, silver carp, rainbow trout. The purpose of such studies is to determine the effectiveness and features of the action of various chemical mutagens, followed by the selection of mutants for further selection.
Research is also underway to study mutagens in microbiology. Mutant strains of microorganisms were obtained that have the ability to destroy harmful substances contained in wastewater from rubber production.
It is quite probable that the power of the new methods manifested itself with particular force in the selection of those organisms in which many individuals can be used to obtain mutations and selection, giving a rapid change of generations. Such conditions are best observed in microorganisms. Many bacteria, fungi, antinomycetes and other forms are of great practical interest for agriculture and medicine. The microbiological industry, which provides amino acids, vitamins, antibiotics, fats and other substances, has enormous opportunities.
Mutation selection has proved to be an indispensable link in the new field of intensive use of the most important microorganisms in the service of man. The influence of radiation or chemical mutagens on molecular structures causes new forms of biochemical processes in the cell.
So, it is possible to obtain radiation and chemical mutants of microorganisms with the properties of "oversynthesis" for the desired substance. It is in this way that the radiation and chemical selection of penicilli, actinomycetes, yeasts and other lower fungi and bacteria has shown the possibility of creating forms that were previously practically impossible to obtain. cultivation techniques plant cells and regeneration of plants from them, developed for many agricultural crops, already now make it possible to experimentally realize the possibilities of cell selection, that is, to use it to create new plant varieties. The list of mutants with important agricultural traits, the selection of which is feasible at the cellular level, is quite large. These include mutants of resistance to stress factors, herbicides, various diseases, overproducers of essential amino acids.
Directions of research, which are solved with the help of cell selection, are not limited to the creation of valuable source material. Cell selection methods underlie a number of technologies for the industrial cultivation of cell cultures, producers of economically significant substances. These lines of research are also important for the development of fundamental questions of mutagenesis, genetics, molecular biology, plant physiology, and biochemistry. Thanks to new technology selection, numerous cell lines and plants have been obtained, which are widely used as starting material for theoretical research. With their use, mutants previously unknown in plants, as well as the first mutants resistant to antibiotics, were isolated.
Application of the achievements of genetic engineering in agriculture very wide. These are the production of food and feed protein, the disposal of substances harmful to the environment, the creation of waste-free production technologies, the production of biogas, the breeding of highly productive animal breeds, new plant varieties that are resistant to diseases, herbicides, insects, and stress.

Mutations are the primary changes upon which evolution and selection are built. The natural manifestation of mutations is a process that is constantly going on in all organisms. It is based on changes in the chemistry of genes, various structural transformations in chromosomes, changes in the number of chromosomes.
Mutational variability underlies any source material for selection, because the original, primary hereditary diversity arises only on the basis of mutations. The ability to control the process of mutations leads to the most serious changes in the whole problem of starting material for selection.
The mutation process can be controlled in different ways. On the one hand, a sharp increase common processes variability leads to a large number of maximum diversity of genes and chromosomes. On the other hand, the use of such factors that have the ability to cause a specific mutation is of paramount importance. In this case, it becomes possible to differentially control the process of mutations, causing a limited circle of necessary mutations, and in the end to obtain only the necessary mutations.
The natural mutation process depends on external factors. Environmental factors form the basis for the appearance of natural mutations. The frequency of mutations in the natural environment can increase under the influence of temperature, ultraviolet light, ionizing measurements, chemical mutagens.
Now it is possible, using environmental factors, to interfere with the chemical structure of genes, causing mutations of genes and chromosomes in any desired amount. This solves the problem of source material for selection in a new way. Methods of induced mutagenesis fundamentally complement all other sections of the doctrine of the source material. Only after passing through strict selection, and in some cases even crossing, mutations can give rise to new varieties. The selection itself is carried out by classical genetic methods, since mutations are only raw material for creating a variety.
The natural mutational process is the basis of the evolutionary transformation of species, and throughout past breeding has been the basis of selection in the creation of plant varieties. As a result of the action of natural and artificial selection, hereditary changes - mutations, depending on their adaptive or economic value, are fixed during sexual or vegetative reproduction or are not subjected to mutations or genetic changes under the influence of environmental changes.
The role of natural and induced mutations in plant and animal breeding, microbiology, biotechnology is great, which is the basis for the successful development of agricultural production.

6. Polyploids: types of polyploids and their use in breeding.

polyploidy. As you know, the term "polyploidy" is used to refer to a wide variety of phenomena associated with a change in the number of chromosomes in cells.

Autopolyploidy is the repeated repetition of the same chromosome set (genome) in a cell. Autopolyploidy is often accompanied by an increase in cell size, pollen grains, and overall size of organisms. For example, the triploid aspen reaches gigantic sizes, is durable, and its wood is resistant to decay. Among cultivated plants, both triploids (bananas, tea, sugar beets) and tetraploids (rye, clover, buckwheat, corn, grapes, as well as strawberries, apple trees, watermelons) are widespread. Some polyploid varieties (strawberries, apple trees, watermelons) are represented by both triploids and tetraploids. Autopolyploids are characterized by high sugar content, high content of vitamins. The positive effects of polyploidy are associated with an increase in the number of copies of the same gene in cells, and, accordingly, in an increase in the dose (concentration) of enzymes. As a rule, autopolyploids are less fertile than diploids, but the decrease in fertility is usually more than offset by an increase in fruit size (apple, pear, grape) or an increased content of certain substances (sugars, vitamins). At the same time, in some cases, polyploidy leads to oppression physiological processes, especially at very high levels of ploidy. For example, 84 chromosome wheat is less productive than 42 chromosome wheat.

Allopolyploidy is the combination of different chromosome sets (genomes) in a cell. Often, allopolyploids are obtained by distant hybridization, that is, by crossing organisms belonging to different species. Such hybrids are usually sterile (they are figuratively called "plant mules"), however, by doubling the number of chromosomes in the cells, their fertility (fertility) can be restored. In this way, hybrids of wheat and rye (triticale), cherry plum and blackthorn, mulberry and tangerine silkworm were obtained.

Polyploidy in breeding is used to achieve the following goals:

Obtaining highly productive forms that can be directly introduced into production or used as material for further selection;

Restoration of fertility in interspecific hybrids;

Transfer of haploid forms to the diploid level.

Under experimental conditions, the formation of polyploid cells can be caused by exposure to extreme temperatures: low (0 ... +8 ° C) or high (+38 ... + 45 ° C), as well as by treating organisms or their parts (flowers, seeds or plant sprouts, eggs or animal embryos) by mitotic poisons. Mitotic poisons include: colchicine (an alkaloid of autumn colchicum - a well-known ornamental plant), chloroform, chloral hydrate, vinblastine, acenaphthene, etc.

7. Classification of source material.

Selection work begins with the selection of source material, on which, as N. I. Vavilov believed, the success of selection work primarily depends.
The source material in breeding is the cultivated and wild forms of plants used to breed new varieties.
The following are used as starting material: 1) forms and varieties of plants that are found in a wide variety in nature; 2) plant forms created in the very process of selection through hybridization and under the artificial influence of various external conditions,
In modern breeding, the following main types and methods of obtaining the source material are used.
I. Natural populations. These include wild forms, local varieties of cultivated plants, and specimens from the world collection of agricultural plants.
II. hybrid populations. There are two types of hybrid populations: 1) intraspecific, obtained as a result of crossing varieties and forms within the same species; 2) created by crossing different species and genera of plants (interspecific and intergeneric).
III. Self-pollinated lines (incubation lines). They serve as an important source of starting material in the breeding of cross-pollinated plants. They are obtained by repeated forced self-pollination of these plants. The best lines are crossed with each other or with varieties to create heterotic hybrids, resulting in hybrid seeds that are used for one year. Hybrids obtained from self-pollinated lines, unlike conventional hybrid varieties, need to be reproduced annually.
IV. Artificial mutations and polyploid forms. This type of source material is created by exposing plants to various types of radiation, chemicals, temperature and other mutagenic agents.
Meaning various kinds source material in the history of the development of breeding and at the present time is not the same. For many centuries, its only form was natural populations. Then genetics theoretically substantiated the use of hybridization. The use of this method in practical selection began in our country in the 1920s. From the 30s. hybridization as a method of creating source material is becoming increasingly important, and at present intraspecific hybridization is its main method when working with almost all cultures. Despite the enormous difficulties of distant hybridization, it is also widely used to create initial material in the selection of a number of important agricultural crops.
Mutations and polyploid forms are new sources of source material, the use of which is expanding every year and, in working with some cultures, gives practically valuable results. Artificial selection has been and remains the most important selection method. However, the selection process includes two groups of activities: evaluation of the source material and selective reproduction (reproduction) of the selected organisms or their parts. Let us consider the methods for evaluating the source material using plants as an example.

In the process of selection, the material is evaluated according to its economic and biological properties, which are the object of selection. But regardless of the characteristics of the object and the tasks of selection, the material is evaluated according to the following criteria:

A certain rhythm of development corresponding to the soil and climatic conditions in which the further exploitation of the variety is planned;

High potential productivity with high product quality;

Resistance to the adverse effects of physical and chemical environmental factors (frost resistance, winter hardiness, heat resistance, drought resistance, resistance to various types of chemical pollution);

Resistance to diseases and pests (assessed by immunity);

Responsiveness to agricultural technology.

Ideally, the variety should not meet individual requirements, but their complex. However, in practice this often turns out to be impossible, and that is why the creation of compositions consisting of lines (clones) with different hereditary properties is considered the fastest and most reliable way to increase the overall stability of agroecosystems. It has been proven that genetically heterogeneous systems there are compensatory interactions of individuals with different characteristics of growth and development, sensitivity to the dynamics of environmental factors, diseases, and pests.

The evaluation of the material is carried out at all stages of ontogeny, since different signs appear in different age states. In this case, the material is evaluated as direct, as well as indirect evidence. For example, when assessing the winter hardiness of winter cereals and perennials, the most important direct indicator is the overall degree of freezing in points. At the same time, winter hardiness can be assessed by determining the content of sugars in cell sap. This indicator is indirect. Evaluation by indirect evidence is considered less accurate, but in some cases it becomes convenient and even inevitable, for example:

If there is a high and stable correlation between direct and indirect signs;

If direct signs appear only in certain years (abnormally dry, rainy ...);

If direct signs appear in the later stages of ontogenesis;

If direct signs are characterized by high modification variability.

To evaluate the breeding material, field, laboratory and laboratory-field methods are used.

Field Methods give the most reliable results, since the material is evaluated in natural conditions by direct signs. However, the use of field methods is not always possible. For example, to assess the frost resistance of annual seedlings, a frosty snowless winter is necessary; if there was no such winter in a given year, then the material remains without evaluation. Similarly, assessment for immunity against natural infestation can only be done in years of high disease or pest prevalence.

Laboratory methods allow you to change the gradation of environmental factors at the will of the experimenter. For example, damage to shoots is simulated by pruning. However, in some cases the use experimental methods requires special equipment; for example, cold hardiness studies require freezers with intense light sources.

Laboratory and field methods combine the advantages and disadvantages of the actual field and laboratory methods.

In a special group are provocative methods, with the help of which it is artificially created provocative background, that is, the conditions for identifying the relationship of plants to unfavorable physico-chemical and biotic factors. The intensity of provocative methods should be optimal. If the provocative background is too weak, the manifestation of an undesirable trait is not guaranteed, and if the background is too harsh, plants that are sufficiently resistant to the action of this factor can be rejected.

Provocative methods include the creation of an infectious background during breeding for resistance to pests and diseases. This direction of selection is extremely important and, at the same time, very difficult, so let's consider it in more detail.

Evaluation of breeding material for resistance to diseases and pests

It is known that people give at least 25% of agricultural products as a tribute to diseases and pests. To reduce these losses, ever-increasing doses of pesticides are used: fungicides, insecticides, acaricides, etc. It is clear that products obtained with the use of pesticides cannot be considered harmless to humans, and the very use of pesticides not only reduces the stability of agroecosystems, but also disrupts the structure of adjacent ecosystems. Therefore, selection for immunity, i.e. resistance to diseases and pests is perhaps the most important component of the breeding process. The foundations of the doctrine of immunity were laid by N.I. Vavilov.

The development of the disease is influenced by environmental factors that create conditions for infection and the spread of the pathogen. Knowledge of these conditions allows you to create the best provocative backgrounds for identifying and culling affected plants. For example, the manifestation of many diseases is facilitated by monoculture, as well as the use of crop rotations with a short rotation.

To identify the resistance or instability of plants to a given pathogen race, an infectious background is created by artificially infecting plants with this race. The resistance or susceptibility of plants to a pathogen is a consequence of co-evolution (conjugated evolution) of two gene pools - a plant and a pathogen. The higher the diversity of these gene pools, the higher the rate of formation of new pathogen races. As a result, the formation of new races in pathogenic organisms proceeds most intensively in the conditions of breeding institutions, where there is the greatest diversity of plant genotypes and pathogen genotypes. As a result, a newly created variety with immunity to this pathogen loses resistance after a few years. To prevent this undesirable effect, the following conditions can be recommended.

1. Create new collection plantings at a sufficient distance from the natural plantations of this species, and, in the cultural circulation, there should not be close species among the predecessors.

2. Create dispersed collections, that is, grow groups of plants that are potentially resistant to a given pathogen in spatial isolation in relation to other similar groups.

8. Remote hybridization. Difficulties in obtaining hybrids Peculiarities of grain crops breeding: scheme of the breeding process.

Modern breeding uses a whole range of methods based on the latest achievements of many sciences: genetics, cytology, botany, zoology, microbiology, agroecology, biotechnology, information technologies etc. (Some of them will be discussed in the lecture "Genetics as the scientific foundation of biotechnology"). However, the main specific methods of selection remain hybridization and artificial selection.

Hybridization

Crossing organisms with different genotypes is the main method for obtaining new combinations of traits. Sometimes hybridization is necessary, for example to prevent inbreeding depression. Inbreeding depression manifests itself in closely related crossing and is expressed in a decrease in productivity and vitality (vitality). Inbreeding depression is the opposite of heterosis (see below).

There are the following types of crosses:

intraspecific crosses- different forms are crossed within a species (not necessarily varieties and breeds). Intraspecific crossings also include crossings of organisms of the same species living in different ecological conditions and / or in different geographical areas ( ecological-geographic crossings). Intraspecific crosses underlie most other crosses.

closely related crosses induction in plants and inbreeding in animals. They are used to obtain clean lines.

Interline crosses- representatives of pure lines are crossed (and in some cases - different varieties and breeds). Interline crossings are used to suppress inbreeding depression, as well as to obtain the effect of heterosis (see below). Interline crossing can act as an independent stage of the breeding process, however, in recent decades, interline hybrids ( crosses, or hybrids of the first generation F1) are increasingly being used to produce commercial products.

Backcrosses (back crosses) are crossings of hybrids (heterozygotes) with parental forms (homozygotes). For example, crosses of heterozygotes with dominant homozygous forms are used to prevent the phenotypic expression of recessive alleles.

Analyzing crosses(they are a kind of back-crosses) are crossings of dominant forms with an unknown genotype and recessive-homozygous tester lines. Such crosses are used to analyze producers by offspring: if there is no splitting as a result of analyzing crosses, then the dominant form is homozygous; if splitting 1:1 is observed (1 part of individuals with dominant traits: 1 part of individuals with recessive traits), then the dominant form is heterozygous.

Saturating (substitution) crosses They are also a type of backcross. With multiple backcrosses, selective (differential) substitution of alleles (chromosomes) is possible, for example, the probability of retaining an undesirable allele can be gradually reduced.

distant crossings- interspecific and intergeneric. Usually, distant hybrids are sterile and are propagated vegetatively; to overcome the infertility of hybrids, doubling the number of chromosomes is used, in this way amphidiploid organisms are obtained: rye-wheat hybrids (triticale), wheat-couch grass hybrids.

Somatic hybridization- this is hybridization based on the fusion of somatic cells of completely dissimilar organisms. Somatic hybridization will be discussed in more detail in the lecture "Genetics as the scientific foundation of biotechnology".

heterosis. During hybridization, it often manifests itself heterosis– hybrid strength, especially in the first generation of hybrids. The mechanisms of heterosis are still poorly understood. Two theories of heterosis are most popular: the theory of dominance and the theory of overdominance. The theory of dominance is based on the idea that when homozygotes are crossed in hybrids of the first generation, unfavorable recessive alleles are transferred to a heterozygous state: AAbb × aaBB → AaBb; then AaBb>AAbb, AaBb>aaBB. The overdominance theory suggests an increased constitutive (general) fitness of heterozygotes compared to any of the homozygotes: aa>AA and aa>aa. There are also more complex ideas about heterosis, for example, the theory of heterosis by V.A. Strunnikova; the essence of this theory is that in pure lines there is an accumulation of modifier genes that suppress the undesirable effects of certain alleles; when crossing different pure lines, each of them brings its own compensatory complex of modifier genes, which enhances the suppression of deleterious alleles.

In some cases, it is possible to preserve the obtained genotypes and thereby fix heterosis, for example, when plants are propagated by vegetative means. The effect of heterosis is also preserved when diploid heterotic hybrids are transferred to the polyploid level.

The crossing of organisms belonging to different species and genera is called distant hybridization.

Distant hybridization is divided into interspecific and intergeneric. Examples of interspecific hybridization are crossing soft wheat with hard wheat, sunflower with Jerusalem artichoke, sowing oats with Byzantine oats, etc. Crossing wheat with rye, wheat with wheatgrass, barley with elimus and others are intergeneric hybridization. The purpose of distant hybridization is the creation of plant forms and varieties that combine the characteristics and properties of different species and genera. In practical and theoretical terms, it is of exceptional interest, since distant hybrids very often are distinguished by increased growth and development capacity, large fruits and seeds, winter hardiness and drought resistance.

The importance of distant hybridization in the development of varieties with resistance to diseases and pests is great.

Remote hybridization has more than two centuries of history. The first distant hybrid between two types of tobacco was obtained in 1760 by I. Kelreuter. Since then, the problem of distant hybridization has consistently attracted the attention of many prominent botanists, geneticists and breeders around the world. A great contribution to the development of the theory and practice of distant hybridization was made by IV Michurin, who, on the basis of this method, created a large number of new varieties and forms of fruit plants.

With distant hybridization, great difficulties are encountered. They are associated with poor crossability or non-crossing of different species and genera and the sterility of the resulting first-generation hybrids.

A number of methods for overcoming the non-crossing of plants with distant hybridization were proposed by IV Michurin. When obtaining hybrids between apple and pear, cherry and bird cherry, quince and pear, apricot and plum, he used a mixture of pollen. Apparently, the release of various pollen, applied to the stigmas of the flowers of the mother plant, contributes to the germination of the pollen of the pollinator species.

In some cases, germination of pollen from the paternal plant was stimulated by the addition of pollen from the mother plant. So, when crossing a rose with a wild rose, I. V. Michurin could not get seeds. When rose pollen was added to rosehip pollen, seeds were formed, and hybrid plants grew from them.

To develop winter-hardy peach varieties, I. V. Michurin decided to cross cultivated peach varieties with a winter-hardy form of wild almond-bean. But he failed to obtain seeds from such crossing. Then he conducted a preliminary crossing of the seedlings of the bean plant with the wild peach of David. The result was a hybrid, which he called the intermediary. It had sufficient winter hardiness and easily crossed with cultivars of peach. This method of stepwise crossing in the hybridization of different plant species is called the mediator method.

With distant hybridization, crosses are carried out on a large scale, since with a small number of pollinated flowers, a misconception can arise about the non-crossing of certain plant species or genera. Interspecific and intergeneric hybrids of the first generation, as a rule, are sterile or have very low fecundity, although their vegetative organs may be well developed.

The reasons for the infertility of hybrids of the first generation of distant crosses are as follows:

• underdevelopment of generative organs. Most often, male generative organs - anthers - are underdeveloped, sometimes they are not even opened. Often sterile and female generative organs;
• meiosis disorder. In the formation of gametes, poor or incorrect conjugation of chromosomes of different species is possible. In this case, two cases are possible.

1. Crossed species have different number chromosomes. For example, species A (2n=14) is crossed with species B (2n=28). In hybrids of the first generation, the number of chromosomes will be 21. During gametogenesis, 7 pairs of bivalents and 7 univalents are formed. Univalent chromosomes are unevenly distributed between the resulting gametes. In this case, gametes with a different number of chromosomes will be formed - from 7 to 14.

2. Crossed species have the same number of chromosomes, but due to their structural differences, conjugation between them can be disrupted. During meiosis, as in the first case, non-homologous chromosomes diverge incorrectly. As a result of this phenomenon, a more or less pronounced sterility of the hybrids is also observed.

To overcome the infertility of distant hybrids of the first generation, the following methods are used.

1. Pollinated by the pollen of one of the parents. This is one of the most commonly used methods and in most cases it gives good results. Its disadvantage lies in the return of the traits and properties of the parent whose pollen was used for re-pollination in subsequent hybrid generations.

2. Pollination by first-generation plant pollen. With a large scale of work and a variety of parental forms, among the hybrids of the first generation, there are usually few plants with fertile pollen. They are used for pollination of sterile plants of the same generation. At the same time, the return to the features of parental forms is much weaker.

3. Treatment of germinating seeds with colchicine solution to double the number of chromosomes. This method makes it possible to obtain a large number of fertile amphidiploid forms with a balanced number of chromosomes.

9. Tasks, organization of the main links of a single breeding and seed production system in the country.

Breeding and seed production in our country is carried out on the basis of a single centralized state system that combines breeding (breeding), testing (state variety testing) and zoning of new varieties, their mass reproduction while maintaining biological and productive qualities (seed production proper), harvesting and monitoring of varietal (approbation) and sowing (seed control) qualities of seeds.

The main links of the selection and seed production system and their tasks can be represented as follows.

1. Selection- breeding of new varieties in breeding centers and other research institutions.

2. Variety testing and zoning- an objective comprehensive assessment of varieties and hybrids in variety plots of the State Commission for Variety Testing of Agricultural Crops and the establishment of areas for their production use.

3. seed production- mass reproduction of varieties and hybrids with the preservation of their varietal and yield qualities. Production of elite seeds and I reproduction in research institutions, educational farms of agricultural universities and subsequent reproductions in specialized seed farms, seed brigades and departments of collective farms and state farms.

4. Procurement and sale of varietal seeds- procurement, storage and sale of varietal seeds by seed farms and procurement organizations. Creation of the necessary insurance and transferable (for winter crops) seed funds for state resources.

5. Variety and seed control- verification of varietal and seed properties of seeds, carried out in all farms and seed state inspections.

Thus, seed work is carried out in the general system of breeding and seed production, but the latter at the same time has its own system.

seed system- this is a group of interrelated production units that, in accordance with the state plan, provide the country's need for high-quality varietal seeds of any crop or group of crops. The seed-growing system provides control over the varietal and sowing qualities of seeds, its task is to harvest and supply high-quality varietal seeds to all collective farms and state farms.

The seed system should be distinguished from the seed scheme.

Seed scheme- this is a group of nurseries and seed crops in which, in a certain sequence, through selection and reproduction, the process of reproducing a variety is carried out. In the same seed production system, this work can be carried out according to different schemes. The seed production system provides for the organization of the production of varietal seeds, while the seed production scheme determines the methods and methods. methods on the basis of which the cultivation of seeds with high varietal and yield qualities is ensured.

The organization of production of varietal seeds of a particular crop or group of crops is built taking into account a number of factors: biological features culture, the area occupied by it in production, feed sowing and yield, organizational and technical conditions, etc.

In 1976, the following system of seed production of cereals, oilseeds and herbs was adopted. Scientific research institutions that originate new varieties provide initial seed material of zoned and promising varieties to experimental production farms of scientific research institutions and educational experimental farms of agricultural universities and technical schools in the amount determined by the USSR State Agrarian Industry.

Experimental production farms of scientific research institutions and educational and experimental farms of agricultural universities and technical schools produce seeds of the elite and I reproductions of zoned and promising varieties in sizes that meet the needs of specialized seed farms, seed brigades and departments of large collective farms and state farms for variety change and variety renewal.

10. The concept of a variety. Types of varieties by origin and methods of creation. The variety is created by man and is a means of agricultural production.

A variety is a group of similar economic and biological properties and morphological features cultivated plants selected and propagated for cultivation in appropriate natural and production conditions in order to increase productivity and product quality. It is important to emphasize the following main points.

1. The group of plants that make up a variety has a common origin. It is the multiplied offspring of one or a few plants.

2. By propagating the parental initial plants, in their offspring, through selection, they achieve similarities in economic and biological properties and morphological characteristics. The degree of this similarity, depending on the source material and selection methods, may be different.

3. The variety is created for cultivation in certain natural and production conditions. In the presence of appropriate natural and production conditions, the variety should provide stable high yields and quality products.

Varieties of agricultural plants differ in origin and breeding methods. By origin, they are divided into local and selective. Local varieties are those created as a result of a long-term action of natural and simple methods of artificial selection in the cultivation of a particular crop in a particular area. A lot of good local varieties of various crops have been created as a result of folk selection. Many of them, having a wide variety of economic and biological characteristics, serve as a valuable source material for breeding breeding varieties.

Breeding called varieties created in research institutions on the basis of scientific breeding methods. They are distinguished by a much greater evenness in morphological characteristics and economic and biological properties: linear varieties, clone varieties, mutant varieties and varieties of hybrid origin.

Population varieties are obtained by mass selection of cross-pollinating or self-pollinating plants. They are genetically heterogeneous. Varieties-populations of self-pollinators are in most cases heterogeneous morphologically and in terms of economic and biological properties. Varieties-populations of cross-pollinators due to constant cross-pollination are highly even. All local varieties and varieties of cross-pollinated crops are population varieties.

Linear called varieties bred by individual selection from self-pollinating crops. A linear variety is a multiplied offspring of one plant, therefore it is highly even in all characteristics and properties. Under the influence of natural pollination, mechanical clogging and mutation, linear varieties gradually lose their uniformity. Linear varieties include winter wheat Ul'yanovka and Gorkovchanka, spring wheat Lutescens 62 and Erythrospermum 841, oats Pobeda and Sovetsky, barley Wiener and Nutans 187, millet Saratovskoe 853, Veselopodolyanskoe 38 and a number of others.

Mutant varieties created by selection from populations obtained under the influence of mutagenic factors. The mutant varieties of winter wheat Kiyanka, spring wheat Novosibirskaya 67, barley Temp and Minsky, soybeans Universal, lupine Kyiv early ripening, beans Sanaris 75, etc. have been zoned.

Varieties obtained by crossing and selecting from hybrid populations are called hybrid. In self-pollinators, they are less aligned than in the line variety. From them, it is sometimes possible to breed new varieties by re-selection. For almost all crops, most of the zoned varieties are hybrids. Among them are winter wheat Bezostaya 1, Priboy and Odesskaya 51, spring wheat Saratovskaya 46, Moskovskaya 35 and Leningradka, oats Drug and Slavutich, barley Odessa 100, Nosovsky 9, millet Early ripening 66 and Saratovskoye 6, rice Start and Spalchik. Sometimes, not one, but several morphologically, homogeneous, but biologically different hybrid lines are selected from a hybrid population. Combining the offspring of such lines gives a hybrid multiline variety. These varieties include winter wheat Odessa 51, spring wheat Moskovskaya 35, spring barley Donetsk 4, etc. Such varieties are characterized by ecological plasticity and occupy large areas.

Clone varieties are obtained by individual selection from vegetatively propagated plants (potato, Jerusalem artichoke, onion, etc.). They are the offspring of one vegetatively propagated plant, therefore they have a very a high degree evenness. Their change occurs under the influence of natural mutagenesis. In potatoes, clone varieties include Zazersky, Skorospelka 1, Maikopsky, etc.

In systematics, the concepts of "form" and "variety" coincide. But this concerns only the botanical and ecological similarities between them. The essential difference is in the origin - the variety is created by man and is a means of agricultural production.

A variety is a group of cultivated plants of the same species similar in economic and biological properties and morphological characteristics, selected and propagated for cultivation in appropriate natural and production conditions in order to increase productivity and product quality.

Copra agricultural plants vary in origin and breeding methods. By origin, they are divided into local, selective and introduced.

Local varieties are those created as a result of a long-term action of natural and elementary methods of artificial selection when cultivating a particular crop in a particular area. Usually they are created by folk selection.

Breeding varieties are called varieties created in research institutions on the basis of scientific breeding methods. As a rule, they have a greater uniformity in their characteristics and properties and have now replaced almost all local varieties.

Varieties that did not previously grow in a given area, but were transferred here from another country or region, are called introduced.

According to the methods of excretion, there are:

Variety populations obtained by mass selection from endogamous and exogamous plants. They are heterogeneous in characters and properties in endogamous forms, and in exogamous plants they are highly even;

Linear varieties bred by individual selection from endogamous plants. In fact, this is the multiplied offspring of one plant. Such a variety is very uniform in characteristics and properties, but this property may be lost as a result of spontaneous mutagenesis, rare cross-pollination and accidental contamination;

Mutant varieties created by selection from populations that have been exposed to mutagenic factors;

Hybrid varieties obtained by crossing and selecting from hybrid populations. Such varieties are less aligned than linear ones and new varieties can be bred from them by repeated selection;

Varietal clones bred by individual selection from vegetatively propagating plants, e.g. potatoes, onions, etc.

Usually such varieties are very uniform in characteristics and properties, but this uniformity can be lost due to natural mutagenesis and contamination.

A specific set of features and properties that a variety should have is determined by three main indicators:

1) soil and climatic conditions for which the variety is created:

2) the level of agricultural technology and mechanization (the use of fertilizers, the use of irrigation):

3) direction in the use of culture (silage or grain for corn, brewing or fodder for barley, early table or technical potatoes, etc.).

Based on the above, the following requirements are formed, which the variety must meet:

High and stable yields over the years and an adequate response to the use of agricultural technology and the use of fertilizers;

Resistance to adverse environmental factors (drought, high or low temperature, etc.);

Complex resistance to diseases and pests;

Adaptability to mechanized cultivation;

High quality products for which the variety is cultivated.

Thus, varieties are created for cultivation in a certain

Soil-climatic zone, and therefore there is not, and cannot be, varieties that are equally suitable for cultivation in different areas. However, some good varieties have a wide genotype reaction rate and are highly plastic, those biologically adapted to a sharp change in the external environment, while maintaining a stable yield. Such varieties can be cultivated over large areas and in various soil and climatic zones.

Similar information.

Mutations at the gene level are molecular structural changes in DNA that are not visible in a light microscope. These include any transformation of deoxyribonucleic acid, regardless of their impact on viability and localization. Some types of gene mutations do not have any effect on the function and structure of the corresponding polypeptide (protein). However, most of these transformations provoke the synthesis of a defective compound that has lost its ability to perform its tasks. Next, we consider gene and chromosomal mutations in more detail.

Characteristics of transformations

The most common pathologies that provoke human gene mutations are neurofibromatosis, adrenogenital syndrome, cystic fibrosis, phenylketonuria. This list can also include hemochromatosis, Duchenne-Becker myopathy and others. These are not all examples of gene mutations. Their clinical signs are usually metabolic disorders (metabolic process). Gene mutations can be:

• Change in the base codon. This phenomenon is called a missense mutation. In this case, a nucleotide is replaced in the coding part, which, in turn, leads to a change in the amino acid in the protein.
• Changing the codon in such a way that the reading of information is suspended. This process is called nonsense mutation. When a nucleotide is replaced in this case, a stop codon is formed and translation is terminated.
• Reading error, frame shift. This process is called "frameshift". With a molecular change in DNA, triplets are transformed during the translation of the polypeptide chain.

Classification

According to the type of molecular transformation, the following gene mutations exist:

• duplication. In this case, repeated duplication or duplication of a DNA fragment from 1 nucleotide to genes occurs.
• deletion. In this case, there is a loss of a DNA fragment from a nucleotide to a gene.
• Inversion. In this case, a 180 degree turn is noted. section of DNA. Its size can be either two nucleotides or a whole fragment consisting of several genes.
• Insertion. In this case, DNA segments are inserted from the nucleotide to the gene.

Molecular transformations involving from 1 to several units are considered as point changes.

Distinctive features

Gene mutations have a number of features. First of all, it should be noted their ability to be inherited. In addition, mutations can provoke the transformation of genetic information. Some of the changes can be classified as so-called neutral. Such gene mutations do not provoke any disturbances in the phenotype. So, due to the innate nature of the code, the same amino acid can be encoded by two triplets that differ in only 1 base. However, a certain gene can mutate (transform) into several different states. It is this kind of change that provokes most of the hereditary pathologies. If we give examples of gene mutations, then we can refer to blood groups. So, the element that controls their AB0 system has three alleles: B, A and 0. Their combination determines blood groups. Relating to the AB0 system, it is considered a classic manifestation of the transformation of normal signs in humans.

Genomic transformations

These transformations have their own classification. The category of genomic mutations includes changes in the ploidy of structurally unaltered chromosomes and aneuploidy. Such transformations are determined by special methods. Aneuploidy is a change (increase - trisomy, decrease - monosomy) in the number of chromosomes of the diploid set, not multiple of the haploid one. With a multiple increase in the number, they speak of polyploidy. These and most aneuploidies in humans are considered lethal changes. Among the most common genomic mutations are:

• Monosomy. In this case, only one of the 2 homologous chromosomes is present. Against the background of such a transformation, healthy embryonic development is impossible for any of the autosomes. Monosomy on the X chromosome is the only one compatible with life. It provokes the Shereshevsky-Turner syndrome.
• Trisomy. In this case, three homologous elements are revealed in the karyotype. Examples of such gene mutations: Down syndrome, Edwards, Patau.

Provoking factor

The reason why aneuploidy develops is considered to be the non-disjunction of chromosomes during cell division against the background of the formation of germ cells or the loss of elements due to anaphase lag, while when moving towards the pole, the homologous link may lag behind the non-homologous one. The concept of "nondisjunction" indicates the absence of separation of chromatids or chromosomes in mitosis or meiosis. This disruption can lead to mosaicism. In this case, one cell line will be normal and the other monosomic.

Nondisjunction in meiosis

This phenomenon is considered the most frequent. Those chromosomes that should normally divide during meiosis remain connected. In anaphase, they move to one cell pole. As a result, 2 gametes are formed. One of them has an extra chromosome, while the other lacks an element. In the process of fertilization of a normal cell with an extra link, trisomy develops, gametes with a missing component - monosomy. When a monosomic zygote is formed for some autosomal element, development stops at the initial stages.

Chromosomal mutations

These transformations are structural changes in the elements. As a rule, they are visualized in a light microscope. Chromosomal mutations usually involve tens to hundreds of genes. This provokes changes in the normal diploid set. As a rule, such aberrations do not cause sequence transformation in DNA. However, when the number of gene copies changes, a genetic imbalance develops due to a lack or excess of material. There are two broad categories of these transformations. In particular, intra- and interchromosomal mutations are distinguished.

Environmental influence

Humans have evolved as groups of isolated populations. They lived long enough in the same environmental conditions. We are talking, in particular, about the nature of nutrition, climatic and geographical characteristics, cultural traditions, pathogens, and so on. All this led to the fixation of combinations of alleles specific for each population, which were the most appropriate for living conditions. However, due to the intensive expansion of the range, migrations, and resettlement, situations began to arise when useful combinations of certain genes that were in one environment in another ceased to ensure the normal functioning of a number of body systems. In this regard, part of the hereditary variability is determined by an unfavorable complex of non-pathological elements. Thus, changes in the external environment and living conditions act as the cause of gene mutations in this case. This, in turn, became the basis for the development of a number of hereditary diseases.

Natural selection

Over time, evolution proceeded in more specific forms. It also contributed to the expansion of hereditary diversity. So, those signs were preserved that could disappear in animals, and vice versa, what remained in animals was swept aside. In the course of natural selection, people also acquired undesirable traits that were directly related to diseases. For example, in the process of development, a person has genes that can determine sensitivity to polio or diphtheria toxin. Becoming Homo sapiens, species people in some way "paid for their rationality" by accumulation and pathological transformations. This provision is considered the basis of one of the basic concepts of the doctrine of gene mutations.

The author of the article is L.V. Okolnova.

X-Men immediately come to mind... or Spider-Man...

But this is the case in cinema, in biology, too, but a little more scientific, less fantastic and more ordinary.

Mutation(in translation - change) - a stable, inherited change in DNA that occurs under the influence of external or internal changes.

Mutagenesis- the process of the appearance of mutations.

The common thing is that these changes (mutations) occur in nature and in humans constantly, almost every day.

First of all, mutations are divided into somatic- occur in the cells of the body, and generative- appear only in gametes.

Let us first analyze the types of generative mutations.

Gene mutations

What is a gene? This is a section of DNA (i.e., several nucleotides), respectively, this is a section of RNA, and a section of a protein, and some sign of an organism.

Those. gene mutation is a loss, replacement, insertion, doubling, change in the sequence of DNA sections.

In general, this does not always lead to illness. For example, when DNA is duplicated, such “mistakes” occur. But they rarely occur, this is a very small percentage of the total, so they are insignificant, which practically do not affect the body.

There are also serious mutagenesis:
- sickle cell anemia in humans;
- phenylketonuria - a metabolic disorder that causes quite serious mental retardation
- hemophilia
- gigantism in plants

Genomic mutations

Here is the classic definition of the term “genome”:

Genome -

The totality of hereditary material contained in the cell of the body;
- the human genome and the genomes of all other cellular life forms are built from DNA;
- the totality of the genetic material of the haploid set of chromosomes of a given species in pairs of DNA nucleotides per haploid genome.

To understand the essence, we greatly simplify, we get the following definition:

Genome is the number of chromosomes

Genomic mutations- change in the number of chromosomes of the body. Basically, their cause is a non-standard divergence of chromosomes in the process of division.

Down syndrome - normally a person has 46 chromosomes (23 pairs), however, with this mutation, 47 chromosomes are formed
rice. down syndrome

Polyploidy in plants (for plants this is generally the norm - most cultivated plants are polyploid mutants)

Chromosomal mutations- deformation of the chromosomes themselves.

Examples (most people have some rearrangements of this kind and generally do not affect either externally or on health, but there are also unpleasant mutations):
- feline crying syndrome in a child
- developmental delay
etc.

Cytoplasmic mutations- mutations in the DNA of mitochondria and chloroplasts.

There are 2 organelles with their own DNA (circular, while the nucleus has a double helix) - mitochondria and plant plastids.

Accordingly, there are mutations caused by changes in these structures.

There is an interesting feature - this type of mutation is transmitted only by the female sex, because. during the formation of a zygote, only maternal mitochondria remain, and the “male” ones fall off with a tail during fertilization.

Examples:
- in humans - a certain form of diabetes mellitus, tunnel vision;
- in plants - variegation.

somatic mutations.

These are all the types described above, but they arise in the cells of the body (in somatic cells).
Mutant cells are usually much smaller than normal cells and are suppressed by healthy cells. (If not suppressed, then the body will be reborn or get sick).

Examples:
- Drosophila eyes are red, but may have white facets
- in a plant, this can be a whole shoot, different from others (I.V. Michurin thus bred new varieties of apples).

Cancer cells in humans

Examples of exam questions:

Down syndrome is the result of a mutation

1)) genomic;

2) cytoplasmic;

3) chromosomal;

4) recessive.

Gene mutations are associated with a change

A) the number of chromosomes in cells;

B) structures of chromosomes;

B) the sequence of genes in the autosome;

D) nucleoside in a DNA region.

Mutations associated with the exchange of regions of non-homologous chromosomes are referred to as

A) chromosomal;

B) genomic;

B) point;

D) gene.

An animal in whose offspring a trait due to a somatic mutation may appear