Defining the concept of “species” seems to be very difficult.
We will consider a species as a historically established set of organisms occupying a certain habitat and characterized by a common origin, a similar system of adaptations to environmental levels, and the reproduction of basic adaptive traits and characteristics over generations.
Organisms of one species have a phenotype and genotype characteristic of that species that are different from those of organisms of another species.
The species occupies a specific range. The distribution area of some species turns out to be wide, and such species are usually polytypic - they include several geographical races, or subspecies. Other species have a much more limited range; they, as a rule, do not form geographical races and are monotypic. The individuals that make up a species do not form a constant, homogeneous mass. Each organism of a species, having common and characteristic features, also has its own individual genotypic characteristics, which together represent the hereditary variability of the species, or, as is sometimes called, the “gene pool” of the species.
A species, representing a single set of organisms, is divided into separate populations. Population called a set of freely interbreeding individuals of the same species, characterized by a common habitat and adaptation to given conditions of existence. The population is formed under the influence of the conditions of existence based on the interaction of factors of heredity, variability, and selection. The formation of populations is a unique way of “fitting” a species to the specific conditions of its existence. Animal breeds and plant varieties created by artificial selection are also represented by separate populations.
The processes of population formation and their dynamics constitute microevolution. The emergence of new species begins with divergence - the division of a species into separate, non-crossing or isolated groups of organisms. A population is a kind of “forge” in which natural selection creates new forms.
In nature, populations of each species are characterized by genetic diversity. But we often don't notice this. Individuals of a population and species appear to us to be relatively uniform in appearance. This relative uniformity of animals and plants, which allows taxonomists to classify animals and plants as certain species, subspecies, and races, is created by natural selection. Selection ensures not only diversity, but also uniformity within a species.
However, this uniformity refers only to the main typical features, characteristics and properties of organisms in a given population. As soon as we begin to genetically analyze the composition of the population in detail, breaking it down into separate lines, we will immediately discover enormous genotypic variability. It turns out that each population, within which individuals crossed with each other for a long time, in a limited area with given climatic conditions inherent in its nature of variability.
The sources of hereditary variability in a population are mutational and combinational variability. The action of genetic laws in a population is the subject of study of population genetics.
In nature, there are no two organisms that are absolutely similar in genotype. Zoologists or botanists who study biological processes in any group of individuals always deal with a hereditarily heterogeneous group of organisms. But since they study the phenotype of organisms, they have the right to neglect the genetic diversity of their material.
The study of a population can be carried out using a purely descriptive method. In this case, the phenotypic characteristics of the population forms are determined, its biological features, find out the conditions of existence and relationships of organisms, food chains, competition, population dynamics over the years and its dependence on various factors. Populations are isolated and formed as a result of the action of many factors: the method of reproduction, the nature of variability, changes in the number of individuals, the pace and direction of selection, climatic, geographic and physiological isolation. The main one is the selection of characteristics that ensure the process of reproduction of generations, i.e. reproduction. It is obvious that when in different ways Reproduction, the emergence and maintenance of populations is carried out in different ways, which can be seen by comparing populations of cross-fertilizing (allogamous) and self-fertilizing (autogamous) organisms.
For the existence of the population are of paramount importance Various types hereditary variability: gene mutations, chromosomal rearrangements and polyploidy. Non-hereditary changes can only play a limited role. Organisms that differ genotypically, for example, in one gene, may not differ morphologically from each other, but have different physiological characteristics (viability, duration of development, fertility). Genetic methods make it possible to get a more complete picture of the hereditary potential of a population, its adaptive characteristics and the direction of evolution.
The pioneers of the study of genetics must be recognized as breeders, because in order to identify the diversity of genotypes in populations, it was necessary to isolate and select for crossing individual pairs of parents and then study their offspring in a series of generations. This is exactly what the breeders did when they created various varieties and breeds. However scientific basis genetic study of populations could only be established after the discovery of G. Mendel, who established quantitative patterns of inheritance.
The first scientific study of a population, combining genetic and statistical methods, was undertaken by the Danish plant physiologist and geneticist V. Johannsen. His classic work On Inheritance in Populations and Pure Lines, published in 1903, marked the beginning of the genetic study of populations. As often happens in science, a classic discovery is made on a seemingly elementary phenomenon and using a simple technique. So in this case, V. Johannsen chose as the object of study populations not cross-pollinating, but self-pollinating plants - barley, beans and peas. Methodologically, this simplified the work, since each such population could be easily divided into groups of descendants of individual individuals, i.e., separate, “pure” lines could be identified. “I call a pure line,” he wrote, “individuals who descend from one self-pollinating individual. From this it is clear that the population of absolute self-pollinators consists only of pure lines, the individuals of which in nature can be mixed, but cannot be affected by crossing.”
The weight and size of the seeds were taken as characteristics. These quantitative traits are determined by the action of many genes, i.e. they are determined polygenically, and are highly susceptible to variability under the influence of factors external environment- soil composition, climate, method of planting, etc. Therefore, to establish the nature of their inheritance, it is necessary to use mathematical methods variability analysis.
For these characteristics there is a pronounced modification, or paratypic, variability. The significance of this variability for evolution in biology has been discussed. various points vision. Proponents of the theory of inheritance of acquired properties believed that changes caused by the influence of environmental factors are inherited and passed on to offspring. Opponents of this theory denied the inheritance of modification changes. The resolution of this dispute in favor of the latter was of fundamental importance, since the selection of organisms by phenotype without identifying hereditary potentials was previously widespread in selection and inhibited the development of animal breeds and plant varieties.
Johannsen weighed the seeds of one bean variety and built a variation series for this indicator. The weight of the seeds was found to be variable ranging from 150 to 750 mg. Subsequently, seeds weighing from 250 to 350 mg were sown separately from seeds weighing 550 to 650 mg. The seeds from each grown plant were weighed again. Since beans are a self-pollinating plant, the genotype of seeds from one plant should be the same, and seeds from different plants there may be genotypic differences. Therefore, heavy seeds (550-650 mg) and light seeds (250-350 mg) selected from a cultivar representative of the population produced plants whose seeds varied significantly in weight. The average weight of seeds on plants grown from heavy seeds was 518.7 mg, and on plants grown from light seeds - 443.4 mg. This showed that a bean variety-population consists of genetically different plants, each of which can become the ancestor of a pure line.
Over the course of 6-7 generations, Johannsen also selected heavy and light seeds from each plant separately, i.e., he selected within pure lines. With such selection, no shift in the series of generations towards heavy or light seeds occurred in any line. Consequently, the variability in seed weight within a pure line was non-hereditary and modification.
As a result of his research, Johannsen came to the following conclusions: 1) “selection in a population causes ... a greater or lesser shift - in the direction of selection - of the average trait around which, fluctuating, the corresponding individuals vary” and 2) “within pure lines regression (degree the similarity of the offspring trait with the maternal one) was... complete; selection within pure lines did not cause any type shift.”
As we can see, the population of autogamous plants consists of genotypically heterogeneous lines. Plants of such a population do not interbreed and do not exchange hereditary information. In this case, the existence of a population is based on strict natural selection of lines of a certain genotype, on the commonality of adaptive mechanisms to similar environmental conditions. In other words, changes in the population of autogamous plants and animals are carried out by the selection of certain hereditarily different lines and clones that have adaptive advantages.
In self-fertilization, a separate organism can be the originator new race, subspecies and species, as well as variety or breed. For example, new variety wheat can be bred from a single grain selected from a population.
However, speaking about high homozygosity in pure lines, it should be borne in mind that even pure lines cannot be absolutely homozygous for the following reasons. Firstly, there are no obligate (absolute) self-pollinating plants. In populations of self-pollinators, for example wheat, tomatoes, etc., plants with one or another frequency are always found open flowering and cross pollination. Because of this, processes of crossing and, accordingly, exchange of hereditary information occur between pure lines in populations, although rarely. Secondly, self-pollinating plants have mutations that prevent self-pollination (incompatibility). Thirdly, in pure lines of self-pollinators, even in one generation, a very noticeable number of diverse mutations arise that violate the homogeneity of the pure line.
Due to these reasons, varieties of self-pollinating plants, when reproduced in production, may lose some of their varietal qualities and require constant monitoring, which is the basis for the need for variety renewal.
During vegetative reproduction of agamic organisms that do not have the sexual process or have lost it for the second time (some protozoa, fungi, algae, etc.), individual clones are the object of selection in the population. The genetic integrity (integration) of such clones in a population is very low due to the impossibility of crosses between individuals of different clones, but such populations apparently still exist in nature and are maintained by selection based on the symbiotic relationships of different genotypes.
In cross-fertilizing organisms in nature, the population is formed on the basis of free crossing of opposite-sex individuals with different genotypes, i.e., on the basis of panmixia. In this case, the hereditary structure of the next generation is reproduced on the basis of various combinations of different gametes during fertilization. It follows that the number of individuals of a particular genotype in each generation will be determined by the frequency of occurrence of different gametes produced by genotypically different parent organisms. This means that traits and properties are preserved and distributed in the population based on patterns of changes in the frequency of gene distribution. These changes are based on the patterns of inheritance discovered by G. Mendel and T. Morgan. Knowing this made it possible to derive rules for the distribution of genes in a panmictic population.
Obviously, those organisms whose genotypes best ensure adaptation to the conditions of existence will produce a larger number of corresponding gametes than those less adapted. Consequently, the frequency (occurrence) of a particular gene in a population will also be determined by natural selection.
Some geneticists call a community of freely interbreeding genotypically different organisms within a species a Mendelian population. We prefer to call it panmictic, since its existence is determined not only by Mendel’s laws, but also by the interaction of all evolutionary factors that ensure freedom of interbreeding of organisms within a population. The diversity of genotypes in a panmictic population is the result of mutational and combinational variability. A newly emerging mutation, in order to become the property of a population, must persist and multiply, that is, become part of the genotypes of a number of organisms. Any mutation in a population has its own fate.
Due to the spread large quantity of various mutations in a population, the genotypes of organisms turn out to be saturated with various mutations, which are most often in a heterozygous state. For example, the number of plants heterozygous for certain mutations can be a fairly high percentage in a population. As the concentration of mutations in a population increases, they become homozygous.
The huge saturation of the population with mutant genes is characteristic not only of cultivated plants and domestic animals, but, as S.S. Chetverikov first showed, also for natural populations. At the same time, mutations occur in the population that differ both in their genetic nature (gene mutations and chromosomal rearrangements) and in their phenotypic manifestation.
To illustrate the division of a panmictic population under the influence of selection, consider a model experiment with an artificially created hybrid population, carried out by American geneticists D. Jones and E. East. These two researchers crossed two varieties of tobacco that differed in the length of the corolla (short and long). Plants of the first generation were crossed with each other, and from the second generation two lines A and B with similar variability in this trait were taken.
The length of the corolla is determined by many genes, and therefore in F 2 it ranged from 52 to 88 mm in these lines. Subsequently, selection was made in the offspring of the taken lines over three generations: in line A - for a short corolla, and in line B - on a long whisk. In each generation, selected forms were crossed within both lines: in line A - with a short corolla, and in line B - with a long corolla. As we see, already in the fifth generation, lines A and B were so different that there was no transition (transgression) between them, i.e. maximum length the corolla in line A was less than the minimum length in line B.
Consequently, by selection and crossing selected forms, it is possible to create lines with a different expression of the trait than that of the original population: selection divides the population into different genotypes. In this experiment, artificial selection was carried out for one trait with deliberate crossing of plants. In nature, natural selection is carried out according to many characteristics and either preserves and maintains the population in an integral state, or decomposes it according to specific conditions of existence.
The study of population genetics is carried out using different methods, the main ones being cytogenetic, ecological-physiological, and mathematical.
The first two methods are used in the analysis of inheritance in a population - to estimate the concentration of mutations and frequencies of mutation. The ecological-physiological method turns out to be necessary to assess the effect of abiotic and biotic factors when determining the adaptive value of phenotypes belonging to genetically different classes of individuals. At the same time, great experimental possibilities are opened up by modeling the action of selection in artificially created synthetic populations with predetermined genetic parameters - the introduction of certain mutations, inversions, translocations, etc. into the population.
The mathematical method allows us to give a strict quantitative description of biological processes. The use of electronic computers has proven particularly promising for modeling the dynamics of the genetic structure of a population, taking into account the complex interaction of many factors. The situations described in this case are significantly closer to reflecting the true, complex and contradictory picture of the evolutionary processes occurring in natural populations of plants and animals.
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1Selection and its tasks. 10-11 grades
1. The group of animals most similar in structure and activity, created for agricultural purposes by man, is called
A) variety; B) view; B) breed; D) by birth.
2. The method of obtaining new varieties of plants by exposing the body to ultraviolet or x-rays is called
A) heterosis; B) polyploidy; B) mutagenesis; D) hybridization.
3. In breeding to obtain new polyploid plant varieties
B) enhancing the growth of adventitious roots; D) increasing plant resistance to unfavorable conditions.
15. Artificial selection - the preservation by man of organisms with characteristics of interest to him over a number of generations - contributes to the emergence
A) variety of plant varieties and animal breeds; B) various types of plants;
B) various types of animals; D) diversity of animal and plant populations.
16. To obtain a high yield of potatoes, they should be hilled several times during the summer so that
A) accelerate the ripening of fruits; B) reduce the number of pests;
C) promote the development of adventitious roots and stolons;
D) improve the nutrition of roots with organic substances.
Test on the topic “BREEDING. BIOTECHNOLOGY"
In animal breeding, inbreeding is carried out for 1) acclimatization 2) improvement of traits 3) increasing heterozygosity 4) consolidation of desired traits
Discovery of N.I. Vavilov centers for the diversity and origin of cultivated plants served as the basis for the creation of1) the main botanical garden2) a collection of seeds of plant species and varieties3) breeding stations4) an institute of genetics
In plant breeding, the polyploidy method is used to obtain
1heterosis phenomena2) pure lines3) high-yielding varieties4) transgenic plants
In breeding for obtaining new polyploid plant varieties
1cross individuals of two pure lines2) cross parents with their descendants3) multiply the set of chromosomes4) increase the number of homozygous individuals
N. I. Vavilov identified the centers of origin of plants
1cultivated2) wild3) light-loving4) herbaceous
What variability causes differences in the phenotypes of identical twins
1gene2) genomic3) modification4) mutation
Mass selection as a selection method, in contrast to individual selection,1 is used to restore the number of bison2) is especially widely used in animal husbandry3) is carried out by genotype4) is carried out by phenotype
A group of plants that are most similar in structure and vital activity, created by selecting individuals with traits useful to humans, is called 1species2) variety3) cultivated plant4) community
Inbreeding of organisms is used in breeding to increase1 vitality2) homozygosity3) heterozygosity4) dominance
It is possible for breeders to obtain polyploid wheat varieties due to mutation1cytoplasmic2) gene3) chromosomal4) genomic
How is the development of new varieties carried out in plant breeding? 1) by growing plants on fertilized soils 2) by vegetative propagation using layering 3) by crossing plants different varieties and subsequent selection of offspring with valuable traits4) growing plants on poor soils
To restore the ability to reproduce in hybrids bred by distant hybridization, 1. polyploid organisms are obtained 2) they are propagated vegetatively 3) heterotic organisms are obtained 4) pure lines are bred
Mutations differ from modifications in that they1.remain in descendants in the absence of the factor that caused them2)occur simultaneously in many individuals in the population3)always have an adaptive character4)cause a certain variability
What phenomenon is observed when two pure lines are crossed with each other and a high-yielding hybrid is obtained as a result? 1 polyploidy 2) heterosis 3) experimental mutagenesis 4) distant hybridization
When pure lines are obtained, the viability of the offspring decreases due to 1 disruption of the meiosis process 2) increased homozygosity 3) the appearance of polyploids 4) the effect of heterosis
The decrease in the effect of heterosis in subsequent generations is due to 1 the manifestation of dominant mutations 2) an increase in the number of heterozygous individuals 3) a decrease in the number of homozygous individuals 4) the manifestation of recessive mutations
Science deals with the production of high-yielding polyploid plants
1 selection2) genetics3) physiology4) botany
To obtain polyploids, a dividing cell is exposed to colchicine, which 1) destroys the nuclear membrane2) destroys the spindle3) increases the rate of cell division4) ensures DNA synthesis during mitosis
The study of patterns of variability in the development of new breeds of animals is the task of science1. selection2) physiology3) botany4) cytology
Breeders use cell engineering methods to obtain
1effective medicines2) hybrid cells and growing hybrids from them3) feed protein for animal nutrition4) food additives for food
A plant population characterized by a similar genotype and phenotype, obtained as a result of artificial selection, is 1.species2) subspecies3) breed4) variety
What underlies the creation of new breeds of farm animals1crossing and artificial selection2) natural selection3) good care for animals, their diet 4) struggle for existence
Artificial selection - the preservation by man of organisms with traits of interest to him over a number of generations - contributes to the emergence of 1. a diversity of plant varieties and animal breeds 2) a variety of plant species 3) a variety of animal species 4) a diversity of animal and plant populations
Individual selection, in contrast to mass selection, is more effective, since it is carried out 1. by genotype 2) under the influence of environmental factors 3) under the influence of human activity 4) by phenotype
The method of obtaining new plant varieties by exposing an organism to ultraviolet or x-rays is called 1 heterosis 2) polyploidy 3) mutagenesis 4) hybridization
The essence of the phenomenon of heterosis used in breeding is a 1-fold increase in the number of chromosomes 2) a change in the gene pool of a variety or breed
3) transition of many genes to a homozygous state 4) heterozygosity of hybrids
The phenomenon of hybrid vigor, manifested in increased productivity and viability of organisms, is called 1 polyploidy 2) mutagenesis 3) heterosis 4) dominance
The effect of heterosis manifests itself due to 1 an increase in the proportion of homozygotes in the offspring 2) the appearance of polyploid individuals in the offspring 3) an increase in the number of mutations in the offspring 4) an increase in the proportion of heterozygotes in the offspring
In plants, pure lines are obtained by 1 cross-pollination 2) self-pollination 3) experimental mutagenesis 4) interspecific hybridization
N.I. Vavilov developed 1 chromosomal theory of heredity 2) evolutionary theory 3) hypothesis of the origin of life 4) the doctrine of the centers of diversity and origin of cultivated plants
Knowledge of the centers of origin of cultivated plants is used by breeders when creating products chemical protection from pests2) determining the number of mutant genes in a variety3) selection source material to obtain a new variety4) studying drift allelic genes in populations
The possibility of selecting parental pairs for crossing and obtaining offspring with the traits desired by the breeder has increased thanks to the discovery of N.I. Vavilov
1 the law of homologous series in hereditary variability 2) centers of diversity and origin of cultivated plants 3) the law of independent inheritance 4) the law of linked inheritance
Distant hybridization(outbreeding) leads to 1) increased heterozygosity of the organism 2) increased homozygosity of the organism 3) disruption of the mitosis process 4) increased fertility
Genetic knowledge is used in breeding for1organization proper care for plants and animals2) creating an optimal diet for animals3) breeding new varieties of plants and animal breeds4) creating optimal conditions keeping animals
The areas where the greatest diversity of plant varieties is concentrated are considered their places of origin, since they1 are located on plains2) concentrated in river valleys3) correspond to modern regions of developed agriculture4) correspond to ancient centers of agriculture
The law of homological series in hereditary variability established
1G. Mendel2) G. D. Karpechenko3) N. I. Vavilov4) T. Morgan
The phenomenon of heterosis is observed in hybrids obtained from1genetically distant parental forms2) inbreeding3) individuals of the same variety, but with different phenotypes4) individuals of the same variety, but with different genotypes
What contribution did G.D. make to genetics and selection? Karpechenko?1overcame the sterility of interspecific hybrids2) developed a new variety of wheat3) discovered the phenomenon of heterosis4) known as the creator of new varieties of fruit
Interline hybridization in plant breeding contributes to 1) obtaining a pure line 2) manifestation of the heterosis effect 3) obtaining polyploids 4) manifestation of mutant genes
The result of cloning strawberries is an organism that has
1original genotype2) another set of chromosomes3) new genotype4) new genotype and phenotype
The South American center of origin of cultivated plants is the birthplace of
1potatoes, pineapples2) rice, sugar cane3) tea, coffee4) tobacco, corn
A pure source line of pea variety can be obtained more quickly
1isolation of self-pollinating lines2) artificial cross-pollination
3) selection of certain plant phenotypes 4) interspecific crossing
As a result of selection, 1 tall pines were bred2) hares that shed in autumn3) diploid varieties of wheat4) various breeds of dogs
Which of the following examples is the result of selection? 1polyploidy of wheat2) echolocation of bats3) molting of hares in autumn4) height of pine trees
Biotechnology uses the ability of bacteria to1) rapidly reproduce2) accumulate toxic substances in their cells3) sporulate under unfavorable conditions4) develop diseases when they enter the body of an animal
The production of hybrids by combining cells of different organisms using special methods is carried out1) cell engineering2) microbiology3) taxonomy4) physiology
The direction of biotechnology in which microorganisms are used to obtain antibiotics and vitamins is called1) biochemical synthesis2) genetic engineering3) cellular engineering4) microbiological synthesis
The production of antibiotics by transplanting a gene into the genome of bacteria is carried out by 1 cell engineering 2) genetic engineering 3) microbiology 4) plant growing
The production of the hormone insulin using bacteria became possible thanks to1) genetic engineering2) cellular engineering3) cytology4) cloning
Obtaining exact copies of the maternal organism became possible thanks to1) genetic engineering2) microbiology3) cellular engineering4) cloning
On this and the next 3 pages of my blog there are test questions Open task bank FIPI
in the 3rd section of biology “Organism as a biological system”.
A total of 1002 tasks were first published in this section on the FIPI website on 101 pages.
31
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In addition to plants,
1) saprotrophic mushrooms
2) bacteria of decay
3) chemosynthetic bacteria
4) cap mushrooms
The decrease in the effect of heterosis in subsequent generations is due to
1) manifestation of dominant mutations
2) an increase in the number of heterozygotes
3) a decrease in the number of homozygotes
4) manifestation of recessive mutations
Using the drawing, determine which features of the tomato fruit (dark or light color, pear-shaped or spherical shape) dominate; what are the genotypes of the parents, genotypes and phenotypes of F1 and F2 hybrids. Make a diagram for solving the problem. The genes for both traits are not linked.
An organism with a genotype heterozygous for two pairs of alleles -
1) AaBb
2) AaBB
3) aaBB
4) AABb
What properties characterize modification variability?
1) is widespread
2) has an individual character
3) not inherited
4) inherited
5) limited by the reaction norm
6) the range of variability has no limits
Animal selection methods used in domestication include
1) hybridization
2) individual selection
3) natural selection
4) interbreeding