clean line
genotypically homogeneous offspring obtained from one self-pollinating (plant) or self-fertilizing (animal) individual through selection and further self-pollination or self-fertilization. It is a group of organisms that are homozygous for most genes. The study of the inheritance of traits in a pure line - important method experimental genetics. Pure lines are sometimes called lines of laboratory animals (e.g. mice) obtained as a result of inbreeding.
Clean line
genotypically homogeneous offspring of constantly self-pollinating plants or self-fertilizing animals, most of whose genes are in the homozygous state. The term was introduced in 1903 by the Danish geneticist W. Johansen, who, in experiments on leguminous plants, proved that in C. l. at same conditions shows a similar phenotype. Ch. l. are derived from a single ancestor and maintained through forced self-pollination and selection. Individuals in Ch. l. reproduce in a number of generations the same hereditarily fixed traits. Ch. l. are important in page - x. production, being the main building blocks plant varieties. Hybridization of two H. l. in some cases leads to the effect of heterosis in the first hybrid generation (this is how some hybrid forms of corn are obtained). Sometimes the term Ch. l. incorrectly applied to the so-called. inbred lines, which are the offspring of animals or plants (cross-pollinated), obtained from one pair of ancestors and maintained in a number of generations through constant inbreeding and selection. Such lines are used in the vast majority genetic research on higher organisms. For example, mechanisms of carcinogenesis and methods of treatment cancer are studied on the so-called. "Ch. l." laboratory mice.
Pure lines in animals with cross-fertilization are obtained by closely related crosses over several generations. As a result, animals that make up a pure line receive identical copies of the chromosomes of each of the homologous pairs.
Clean line
Clean line- a group of organisms that have some characteristics that are completely transmitted to offspring due to the genetic homogeneity of all individuals. In the case of a gene that has multiple alleles, all organisms belonging to the same pure lineage are homozygous for the same allele for that gene.
Pure lines are often called plant varieties that, when self-pollinated, give genetically identical and morphologically similar offspring.
An analogue of a pure line in microorganisms is a strain.
Pure (inbred) lines in animals with cross-fertilization are obtained by closely related crosses over several generations. As a result, animals that make up a pure line receive identical copies of the chromosomes of each of the homologous pairs.
Use of clean lines in scientific research
Pure lines of peas were used for crossing in their experiments by the discoverer of the laws of heredity, Gregor Mendel. In 1903, the geneticist W. Johansen showed the inefficiency of selection in pure lines, which played an important role in the development evolutionary theory and breeding practices.
Currently clean lines animals (primarily rats and mice) and plants play essential role in carrying out biological and medical research. The genetic homogeneity of the organisms used by scientists increases the reproducibility of the results and reduces the likelihood of genetic differences between individuals (for example, in the control and experimental group) affecting the result of the study. Through traditional breeding and methods genetic engineering many pure lines with desired properties (for example, increased propensity to consume alcohol, high incidence of different forms cancer, etc.) used for specific studies.
The use of pure (inbred) lines in breeding
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Genotypically homogeneous offspring obtained from one self-pollinating (plant) or self-fertilizing (animal) individual through selection and further self-pollination or self-fertilization. It is a group of organisms that are homozygous for... Big Encyclopedic Dictionary
Genotypically homogeneous offspring obtained initially from one self-pollinating or self-fertilizing individual through selection and further self-pollination (self-fertilization). The term was introduced in 1903 by W. Johansen. Since self-pollination ... ... Biological encyclopedic dictionary
clean line- Offspring obtained in a series of generations from 1 individual (if there is a possibility of self-fertilization, used in the future, the closest possible inbreeding); also the concept of "Ch.l." used to denote lines obtained originally from ... Technical Translator's Handbook
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Pure line Offspring obtained in a series of generations from 1 individual (if there is a possibility of self-fertilization, used in the future, the closest inbreeding
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clean line- grynoji linija statusas T sritis augalininkystė apibrėžtis Genotipiškai vienodi palikuonys, gauti iš homozigotinio savidulkio individo. atitikmenys: engl. pure line rus. clean line … Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas
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Genotypically homogeneous offspring of constantly self-pollinating plants or self-fertilizing animals, most of whose genes are in the homozygous state. The term was introduced in 1903 by the Danish geneticist V. Johansen, who in ... ... Great Soviet Encyclopedia
Clean line- a group of organisms that have some characteristics that are completely transmitted to offspring due to the genetic homogeneity of all individuals. In the case of a gene that has multiple alleles, all organisms belonging to the same pure lineage are homozygous for the same allele for that gene.
Pure lines are often called plant varieties that, when self-pollinated, give genetically identical and morphologically similar offspring.
An analogue of a pure line in microorganisms is a strain.
Pure (inbred) lines in animals with cross-fertilization are obtained by closely related crosses over several generations. As a result, animals that make up a pure line receive identical copies of the chromosomes of each of the homologous pairs.
Use of clean lines in scientific research
Pure lines of peas were used for crossing in their experiments by the discoverer of the laws of heredity, Gregor Mendel. In 1903, the geneticist W. Johansen showed the inefficiency of selection in pure lines, which played an important role in the development of evolutionary theory and breeding practice.
Currently, pure lines of animals (primarily rats and mice) and plants play an important role in biological and medical research. The genetic homogeneity of the organisms used by scientists increases the reproducibility of the results and reduces the likelihood of genetic differences between individuals (for example, in the control and experimental group) affecting the result of the study. With the help of traditional breeding and genetic engineering methods, many pure lines with desired properties have been obtained (for example, increased propensity to consume alcohol, high levels of
To improve the breeding and productive qualities of animals, it is necessary to know the genotypes of not only individual individuals, but also the genetic structure of the entire herd or even the breed as a whole. Importance for selection, they have knowledge of the laws of heredity and variability in the absence and taking into account artificial selection and selection of animals, the factors that determine them. Studies of genetic processes occurring in the natural conditions of animal reproduction have great importance for further knowledge of evolution in order to control these processes in the breeding of farm animals.
According to N.V. Timofeev-Resovsky, a population is a collection of individuals of a given species, for a long time ( a large number generations) inhabiting a certain space, consisting of individuals that can freely interbreed with each other, and separated from the same neighboring populations by one of the forms of isolation (spatial, seasonal, physiological, genetic). For example, the reindeer of the Kolguev Island are isolated from the reindeer bred on the mainland of the Far North by a wide strip of sea
As a result, a special population of Kolguev deer was formed, which differs from the other part of this species in genotypic and phenotypic traits - they are larger and have better viability.
In animal husbandry, a population is understood as a group of animals of the same species, characterized by a certain number and distribution area. Such a group differs from other populations in its genetic structure, exterior, interior and productive qualities. A livestock population can be a single herd of animals, a breed or offspring. Usually a population is a closed group. The import into or export from it of animals from other populations is limited, therefore, reproduction in the population is carried out by selecting males and females belonging to this population. AT Yaroslavl region for example, a population of cattle of the Yaroslavl breed is bred.
Each population is characterized by a certain gene pool, i.e., a set of alleles that make up its composition.
Along with the population in genetics, there is the concept of "pure line" - this is the offspring obtained from only one parent and having a complete resemblance to it in genotype
Pure lines can be created in crop production in self-pollinating plants. Unlike populations, they are characterized by complete homozygosity. Due to complete homozygosity, selection in a pure line is impossible, since all individuals included in it have an identical set of genes. Highly homozygous linear mice, rats and other laboratory animals are created for the purpose of conducting various experiments, for example, to test for the mutagenicity of certain drugs, evaluate vaccines, etc.
The population consists of animals of different genotypes. The efficiency of selection in it depends on the degree of genetic variability - the ratio of dominant and recessive genes. Hardy and Weinberg held mathematical analysis distribution of genes in large populations, where there is no selection, mutation and mixing of populations.
In accordance with this, the Hardy-Weinberg law or rule was formulated, according to which, in the absence of factors that change gene frequencies, populations at any ratio of alleles from generation to generation keep these allele frequencies constant. Despite the well-known limitations, using the Hardy-Weinberg formula, it is possible to calculate the population structure and determine the frequencies of heterozygotes (for example, by lethal or sublethal genes, knowing the frequencies of homozygotes for recessive traits and the frequencies of individuals with a dominant trait), analyze shifts in gene frequencies for specific traits in the result of selection, mutations and other factors.
A population is in equilibrium only when there is no selection in it. When individual animals are culled in such a population, the ratio of gametes changes, which affects the genetic structure of the next generation. However, K. Pearson showed that as soon as the state of panmixia (free crossing) occurs, the ratio of genotypes and phenotypes in the population in the next generation returns to that which corresponds to the Hard-Weinberg formula, but with a different ratio. Crossing, restoring the ratio of genotypes in the population, in accordance with the Hardy-Weinberg formula, was called stabilizing. From this follows the conclusion: when random, unselected sires or queens are used in a population, stabilization of productivity traits at the same level is observed, and it is impossible to increase the productivity of animals in such a situation. Similarly, in the absence of culling of heterozygous carriers of recessive anomalies, the frequency of manifestation of abnormal animals in the population remains unchanged.
In populations of farm animals, gene frequencies are constantly changing, which can be observed when analyzing adjacent generations. Such changes are the essence genetic evolution. The main factors of evolution: mutations, natural and artificial selection, migration, genetic drift.
One of the main causes of genetic variation in a population is mutations. Spontaneous mutations of each gene occur at a low frequency, but the overall mutation rate of all genes that contain populations is very high. Mutations that occur in the germ cells of the parental generation lead to a change in the genetic structure of the offspring. In a population of constant size in the absence of selection, most of the resulting mutations are quickly lost, but some of them can be preserved in a number of generations. The disappearance of mutant genes from the population is opposed by the action of the mutation process, which results in the formation of repeated mutations.
The genetic structure of populations is formed and changed under the influence of natural and artificial selection. Action natural selection consists in the fact that individuals with high vitality, precocity, fecundity, etc., i.e., those more adapted to environmental conditions, have predominant reproduction. With artificial selection, the signs of productivity are of decisive importance.
IN AND. Vlasov notes that natural selection occurs at all stages of the ontogenesis of a population - from the formation of gametes to an adult organism. At the same time, it significantly affects the rate of artificial selection due to the opposite effect during selection for high level development of productive traits, unusual for species biological boundaries. Based on this, when selecting animals, it is necessary to take into account not only productive traits, but also signs of adaptability to environmental conditions.
According to S.M. Gershenzon, the criterion for the intensity of natural selection is the difference in the fitness of the compared groups, called the selection coefficient and expressed in fractions of a unit. For example, if the probability of leaving offspring by individuals with the aa genotype is 10% less than by individuals with the AA or Aa genotype, then the fitness of these groups for individuals of AA and Aa is 1, for individuals of aa - 0.9.
From the point of view of veterinary genetics, the effectiveness of selection against harmful mutations, primarily of the recessive type, is important. The analysis shows that the high frequencies of the recessive mutant gene can be quickly reduced to low values by selection. To reduce the frequency of a lethal gene, for example from 0.3 to 0.2, two generations are sufficient.
The frequency of homozygotes (aa) for the mutant gene depends on the frequency of heterozygous animals in the population. The identification of these heterozygotes and their elimination, respectively, will reduce the frequency of genetic anomalies caused by the mutant gene, which is especially important at a high mutation rate.
The genetic structure of a population can change due to random genetic-automatic processes (according to N.P. Dubinin) or genetic drift (according to S. Wright). Observations show that gene drift occurs most intensively in small populations. For example, cases of high concentrations of rare mutations in small isolated populations of cattle and other animal species are known, apparently associated with genetically automatic processes. The spread of mutations in different animal populations can occur as a result of migrations.
Mating of animals in family relations is called inbreeding. Related mating, or inbreeding, is a selection method used in livestock breeding to consolidate valuable hereditary traits of an animal in subsequent generations. In related animals, there is a similarity in certain pairs of alleles that they received from a common ancestor. This similarity is greater, the closer the degree of relationship.
Each animal in the genotype has allelic genes, both in the homozygous and in the heterozygous state. The heterozygote usually contains deleterious mutated recessive genes. Inbreeding increases the probability of fusion of identical gametes carrying mutant genes in the heterozygous state and their transition to the homozygous state. This probability is proportional to the degree of relatedness of mated animals.
Thus, as a result of the use of inbreeding, a change in gene frequencies occurs, the probability of separating recessive homozygotes increases, which is the cause of inbreeding depression, which is expressed in a decrease in the viability, fertility of animals, and the birth of abnormal individuals.
Inbreeding, as a rule, was complex - simultaneously on two (1st digit) or three (2nd digit) ancestors.
Imbreeding depression, in terms of indicators characterizing the productivity and viability of animals, is not a fatal companion of related mating.
There are many examples of when inbreeding different degrees, including relatives, no negative effects were observed.
N.P. Dubinin notes in this regard that “the line is deteriorating while the processes of sequential accumulation of harmful recessive genes passing into the homozygous state are going on in it. When a more or less pronounced completion of this process occurs, the lines become relatively constant in their properties and can remain in such a stable state for a long time. Only new accumulated mutations can change the genotype of such lines.” However, the academician emphasizes, “many lines die during inbreeding, of course, because lethal and semi-lethal genes pass into the homozygous state in them.” Therefore, inbreeding is used as a method of individual selection for transferring valuable genes of outstanding animals into a homozygous state.
In the course of the long evolution of animals, along with beneficial mutations picked up by selection, a certain range of genes and genes has accumulated in populations or breeds. chromosomal mutations. Each generation of the population inherits this load of mutations, and in each of them new mutations arise, some of which are transmitted to subsequent generations.
Obviously, most harmful mutations are swept aside by natural selection or eliminated in the selection process. These are, first of all, dominant gene mutations, phenotypically manifested in the heterozygous state, and quantitative changes in chromosome sets. Recessively acting gene mutations in the heterozygous state and structural rearrangements of chromosomes that do not noticeably affect the viability of their carriers can pass through the selection sieve. They form the genetic load of the population. Thus, the genetic load of a population is understood as the totality of harmful gene and chromosomal mutations. Distinguish between mutational and segregation genetic load. The first is formed as a result of new mutations, the second - as a result of splitting and recombination of alleles when heterozygous carriers of "old" mutations are crossed.
The frequency of lethal, semi-lethal and sub-vital mutant genes transmitted from generation to generation in the form of a mutational genetic cargo, due to the difficulty of identifying carriers, cannot be accurately accounted for. Morton and Crow proposed a form for calculating the level of genetic load in terms of lethal equivalents. One lethal equivalent corresponds to one lethal gene that causes mortality with a 10% probability, two lethal genes with a 50% probability of death, etc. The value of the genetic load according to the Morton formula:
log eS = A + BF,
where S is the surviving part of the offspring;
A - mortality measured by the lethal equivalent in the population under the condition of random mating (F = 0), plus mortality due to external factors;
B - expected increase in mortality when the population becomes completely homozygous (F= 1);
F - coefficient of inbreeding.
The level of genetic load can be determined on the basis of the phenotypic manifestation of mutations (malformations, congenital metabolic anomalies, etc.), analysis of their inheritance type, and frequency in the population.
N.P. Dubinin proposes to determine the genetic load of a population by comparing the frequencies of stillbirths in related and unrelated selections of parental pairs. At the same time, it should be borne in mind that at a high frequency of heterozygotes for recessive lethal and semi-lethal mutant genes, the birth of animals with anomalies should not necessarily be associated with close and moderate inbreeding. common ancestor(the source of the mutation) may also be in the distant ranks of the pedigree. For example, the bull Truvor 2918, a heterozygous carrier of the mutant recessive gene, was in the V, VI, VII ranks of ancestors at the Krasnaya Baltika state farm, but when using his great-great-grandson Avtomat 1597, cows related to him were observed mass cases birth of hairless calves.
These data to a certain extent characterize the levels of genetic load for individual mutant genes in specific cattle populations.
Chromosomal mutations are integral part genetic cargo. They are accounted for directly. cytological method. According to the results of numerous studies, the main component of the load of chromosome aberrations in cattle are Robertsonian translocations, and in pigs - reciprocal ones. The most common mutation in cattle was the translocation of chromosome 1/29. The range of variability in the frequency of this aberration, according to our data, in populations of fawn-motley cattle ranged from 5 to 26%.
Thus, the concept of genetic cargo in the light of modern advances in cytogenetics should be expanded. Now that a wide range of chromosome aberrations is known and the strict inheritance of some of them (translocations and inversions) has been established, it seems appropriate to take them into account, along with harmful gene mutations, as an integral part of the genetic load.
Existence in populations hereditary variability, primarily mutations in the heterozygous state, allows them to quickly adapt to new environmental conditions by changing the genetic structure. The mutation process also leads to the formation in populations genetic polymorphism- diversity of allele frequencies, homozygotes for dominant, heterozygotes or homozygotes for recessive genes. Polymorphism is a mechanism that maintains the existence of populations. If, for example, heterozygosity provides better adaptability to changing environmental conditions, then there is a selection in favor of heterozygotes, which leads to balanced polymorphism - the reproduction in a population from generation to generation of a certain ratio of different genotypes and phenotypes. The processes that ensure the ability of a population to maintain its genetic structure are called genetic homeostasis.
In genetics, two classes of traits are distinguished - qualitative and quantitative. They differ in the nature of variability and features of inheritance. Qualitative features are characterized by discontinuous, and quantitative - continuous variability. The first of them give clear boundaries when splitting into dominant or recessive traits. This is because each of them is usually controlled by one allelic gene. Quantitative features do not give clear boundaries for splitting when different options crosses, although they differ from high-quality more a high degree variability. A feature of quantitative traits is complex nature inheritance. Each of them is determined not by one, but by many loci in the chromosomes. This type of inheritance, when one trait is determined by many genes, is called polygenic. The level of development of a quantitative trait depends on the ratio of dominant and recessive genes, other genetic factors and degree of modifying action of factors external environment. Variability by quantitative attribute in a population is made up of genetic and paralogical (external) variability.
The concept of the heritability of traits and the coefficient of heritability. Different quantitative traits have an unequal degree of genetic variability, and environmental conditions have a different effect on the level of phenotypic manifestation of a particular trait. When selecting animals, it is of paramount importance to know to what extent the levels of development of a quantitative trait will coincide in parents and offspring, or to what extent the descendants will inherit quantitative economically useful traits or pathological traits of their parents.
Economically useful traits include milk production, fat and protein content in cows' milk, wool shearing in sheep, egg production in chickens, live weight gain, fertility, etc. An increase in the level of development of economically useful traits is achieved by constant selection of the best individuals for reproduction. The effectiveness of selection for these traits depends on the degree of their heritability, the relationship between them, the difference between the average value of the trait of the selected group and the average for the herd (selection differential) and the interval between generations.
The values of the coefficients of heritability depend on the nature of the trait. So, the average value of A2 for milk yield is 0.25, milk fat content - 0.38, live weight in sheep - 0.35, pure wool yield - 0.55, fertility in cattle - 0.08, etc.
Breeding practice and special studies have accumulated data indicating that in some cases the level of development of one or more traits in the offspring exceeds the degree of expression of these traits in the best of the parents. This phenomenon, called heterosis, does not fit into the usual framework of trait inheritance. Various hypotheses have been proposed to explain it:
1) heterozygous state for many genes;
2) interactions of dominant favorable genes;
3) overdominance, when heterozygotes are superior to homozygotes.
N.V. Turbin proposed the theory of genetic balance, which is based on the complex nature of causal relationships between hereditary factors and traits.
N.G. Dmitriev and I.JI. Galperin note that the main reason for the emergence of heterosis must be sought in the features of the evolution of a species, breed, line. It should be borne in mind that everything in nature is aimed at preserving life. The manifestation of heterosis depends on the genetic nature of the trait. So, with interbreeding or interline crossing, heterosis is more pronounced in relation to traits that have a low degree of heritability
As for traits with medium or high heritability, heterosis for them is most often weak, and hybrids usually occupy an intermediate position.
In the presence of true heterosis, the value of the index or more than 100%. If the value of heterosis is less than 100% or has a minus sign, then it is more correct to speak of the best or worst combinational ability of the lines. Crossing the latter according to a certain scheme ensures in the hybrid offspring the best development of one trait from the father, and the other from the mother, although this trait in the hybrid does not exceed the best parental form in its development.
Heredity and variability are properties of organisms. Genetics as a science
Heredity- the ability of organisms to transmit their characteristics and features of development to offspring.
Variability- a variety of characters among representatives of this species, as well as the property of offspring to acquire differences from parental forms.
Genetics- the science of the laws of heredity and variability.
2. Describe the contribution of scientists known to you to the development of genetics as a science by filling out the table.
History of the development of genetics
3. What methods of genetics as a science do you know?
The main method of genetics is hybridological. This is the crossing of certain organisms and the analysis of their offspring. This method was used by G. Mendel.
Genealogical - the study of pedigrees. Allows you to determine the patterns of inheritance of traits.
Twin - comparison of identical twins, allows you to study modification variability (determine the impact of the genotype and environment on the development of the child).
Cytogenetic - the study under a microscope of the chromosome set - the number of chromosomes, the features of their structure. Allows detection of chromosomal diseases.
4. What is the essence hybridological method studying the inheritance of traits?
The hybridological method is one of the methods of genetics, a method of studying the hereditary properties of an organism by crossing it with a related form and then analyzing the characteristics of the offspring.
5. Why Peas Can Be Counted successful object genetic research?
Pea species differ from each other in a small number of well-distinguishable characters. Peas are easy to grow, in the Czech Republic it breeds several times a year. In addition, in nature, peas are self-pollinators, but in the experiment, self-pollination is easily prevented, and the researcher can easily pollinate a plant with one pollen from another plant.
6. Inheritance of what pairs of traits in peas was studied by G. Mendel?
Mendel used 22 pure pea lines. The plants of these lines had strongly pronounced differences from each other: the shape of the seeds (round - wrinkled); color of seeds (yellow - green); bean shape (smooth - wrinkled); arrangement of flowers on the stem (axillary - apical); plant height (normal - dwarf).
7. What is meant in genetics by a clean line?
A pure line in genetics is a group of organisms that have some characteristics that are completely transmitted to offspring due to the genetic homogeneity of all individuals.
Patterns of inheritance. monohybrid cross
1. Give definitions of concepts.
allelic genes- genes responsible for the manifestation of one trait.
Homozygous organism An organism that contains two identical allelic genes.
heterozygous organism An organism that contains two different allelic genes.
2. What is meant by monohybrid crossing?
Monohybrid crossing - crossing forms that differ from each other in one pair of alternative traits.
3. Formulate the uniformity rule for hybrids of the first generation.
When crossing two homozygous organisms that differ from each other in one trait, all hybrids of the first generation will have the trait of one of the parents, and the generation will given feature will be uniform.
4. Formulate a splitting rule.
When two descendants (hybrids) of the first generation are crossed with each other in the second generation, splitting is observed and individuals with recessive traits appear again; these individuals make up ¼ of the total number of descendants of the first generation.
5. Formulate the law of purity of gametes.
When formed, only one of the two “elements of heredity” responsible for this trait falls into each of them.
6. Using generally accepted conventions, make a scheme of monohybrid crossing.
Describe on this example cytological basis of monohybrid crossing.
P is the parental generation, F1 is the first generation of offspring, F2 is the second generation of offspring, A is the gene responsible for the dominant trait, and the gene responsible for the recessive trait.
As a result of meiosis, in the gametes of the parent individuals, there will be one gene responsible for the inheritance of a certain trait (A or a). In the first generation, somatic cells will be heterozygous (Aa), so half of the gametes of the first generation will contain the A gene, and the other half will contain the a gene. As a result of random combinations of gametes in the second generation, the following combinations will arise: AA, Aa, aA, aa. Individuals with the first three combinations of genes will have the same phenotype (due to the presence of a dominant gene), and with the fourth - a different (recessive).
7. Solve the genetic problem for monohybrid crossing.
Task 1.
In watermelon, the green color of the fruit dominates over the striped. From the crossing of a green-fruited variety with a striped-fruited one, hybrids of the first generation were obtained, having fruits of a green color. The hybrids were pollinated and received 172 hybrids of the second generation. 1) How many types of gametes does a green-fruited plant form? 2) How many F2 plants will be heterozygous? 3) How many different genotypes will there be in F2? 4) How many plants with striped fruit will be in F2? 5) How many homozygous plants with green fruits will be in F2?
Decision
A - green color, a - striped color.
Since when plants with green and striped fruits were crossed, plants with a green fruit were obtained, it can be concluded that the parental individuals were homozygous (AA and aa) (according to Mendel's rule of uniformity of hybrids of the first generation of Mendel).
Let's make a crossover scheme.
Answers:
1. 1 or 2 (in case of heterozygote)
2. 86
3. 3
4. 43
5. 43.
Task 2.
Long hair in cats is recessive to short hair. A longhair cat crossed with a heterozygous shorthair cat produced 8 kittens. 1) How many types of gametes does a cat have? 2) How many types of gametes are formed in a cat? 3) How many phenotypically different kittens are in the litter? 4) How many genotypically different kittens are in the litter? 5) How many kittens are in the litter with long hair?
Decision
A is short hair and a is long hair. Since the cat had long hair, it is homozygous, its genotype is aa. The cat has the Aa genotype (heterozygous, short hair).
Let's make a crossover scheme.
Answers:
1. 2
2. 1
3. 4 long and 4 short
4. 4 with the Aa genotype, and 4 with the aa genotype
5. 4.
multiple alleles. Analyzing cross
1. Give definitions of concepts.
Phenotype- the totality of all the signs and properties of the body that are revealed in the process individual development under these conditions and are the result of the interaction of the genotype with a complex of factors of the internal and external environment.
Genotype- This is the totality of all the genes of an organism, which are its hereditary basis.
2. Why are the concepts of dominant and recessive genes relative?
A gene for a trait may have other "conditions" that are neither dominant nor recessive. This phenomenon can occur as a result of mutations and is called "multiple allelism".
3. What is meant by multiple allelism?
Multiple allelism is the existence of more than two alleles of a given gene in a population.
4. Fill in the table.
Types of interaction of allelic genes
5. What is analyzing cross and what is its practical significance?
Analyzing crosses are used to establish the genotype of individuals that do not differ in phenotype. In this case, the individual whose genotype needs to be established is crossed with an individual homozygous for the recessive gene (aa).
6. Solve the problem of analyzing crossover.
Task.
The white color of the corolla in phlox dominates over pink. A plant with a white corolla is crossed with a plant with a pink color. 96 hybrid plants were obtained, of which 51 are white and 45 are pink. 1) What are the genotypes of the parent plants? 2) How many types of gametes can a plant with a white corolla color form? 3) How many types of gametes can a plant with a pink corolla color form? 4) What phenotype ratio can be expected in the F2 generation from crossing F1 hybrid plants with white flowers?
Decision.
A - white color, a - pink color. The genotype of one plant A .. is white, the second aa is pink.
Since splitting 1:1 (51:45) is observed in the first generation, the genotype of the first plant is Aa.
Let's make a crossover scheme.
Answers:
1. Aa and aa.
2. 2
3. 1
4. 3 with white corolla: 1 with pink corolla.
Dihybrid cross
1. Give definitions of concepts.
Dihybrid cross- crossing individuals, which take into account differences from each other in two ways.
Punnett lattice is a table proposed by the English geneticist Reginald Punnett as a tool that represents graphic recording to determine the compatibility of alleles from parental genotypes.
2. What ratio of phenotypes is obtained by dihybrid crossing of diheterozygotes? Illustrate your answer by drawing a Punnett lattice.
A - Yellow color of seeds
a - Green color of seeds
B - Smooth seed shape
c - Wrinkled form of seeds.
Yellow smooth (AABB) × Green wrinkled (AABB) =
P: AaBv×AaBb (diheterozygotes)
Gametes: AB, Av, aB, av.
F1 in the table:
Answer: 9 (yellow smooth): 3 (green smooth): 3 (yellow wrinkled): 1 (green wrinkled).
3. Formulate the law of independent inheritance of traits.
In a dihybrid cross, the genes and traits for which these genes are responsible are inherited independently of each other.
4. Solve genetic problems for dihybrid crossing.
Task 1.
Black color in cats dominates over fawn, and short hair dominates over long. Crossed purebred Persian cats (black longhair) with Siamese (fawn shorthair). The resulting hybrids were crossed with each other. What is the probability of getting a purebred Siamese kitten in F2; a kitten phenotypically similar to a Persian; long-haired fawn kitten (express in parts)?
Decision:
A - black color, and - fawn.
B - short hair, c - long.
Let's create a Punnett lattice.
Answer:
1) 1/16
2) 3/16
3) 1/16.
Task 2.
In tomatoes, the round shape of the fruit dominates over the pear-shaped, and the red color of the fruit dominates over the yellow. 120 plants were obtained from crossing a heterozygous plant with a red color and a pear-shaped fruit and a yellow-fruited plant with rounded fruits. 1) How many types of gametes does a heterozygous plant with a red color of fruits and a pear-shaped form form? 2) How many different phenotypes are obtained from such crossing? 3) How many different genotypes were obtained from such a crossing? 4) How many plants turned out with a red color and a rounded shape of the fruit? 5) How many plants turned out with a yellow color and a rounded shape of the fruit?
Decision
A - rounded shape, a - pear-shaped.
B - red color, c - yellow color.
We determine the genotypes of the parents, the types of gametes and write down the crossing scheme.
Let's create a Punnett lattice.
Answer:
1. 2
2. 4
3. 4
4. 30
5. 30.
Chromosomal theory of heredity. Modern views about the gene and the genome
1. Give definitions of concepts.
Crossing over- the process of exchanging sections of homologous chromosomes during conjugation in prophase I of meiosis.
Chromosomal map- this is a diagram relative position and relative distances between the genes of certain chromosomes that are in the same linkage group.
2. In what case does the violation of the law of independent inheritance of traits occur?
When crossing over, Morgan's law is violated, and the genes of one chromosome are not inherited linked, since some of them are replaced by allelic genes of the homologous chromosome.
3. Write the main points chromosome theory T. Morgan's heredity.
A gene is a section of a chromosome.
Allelic genes (genes responsible for one trait) are located in strictly certain places(loci) of homologous chromosomes.
Genes are arranged linearly on chromosomes, that is, one after another.
During the formation of gametes between homologous chromosomes conjugation occurs, as a result of which they can exchange allelic genes, that is, crossover can occur.
4. Formulate Morgan's law.
Genes located on the same chromosome during meiosis fall into the same gamete, that is, they are inherited linked.
5. What determines the probability of divergence of two non-allelic genes during crossing over?
The probability of divergence of two non-allelic genes during crossing over depends on the distance between them in the chromosome.
6. What underlies the compilation of genetic maps of organisms?
Calculation of the frequency of crossing over between any two genes of the same chromosome responsible for various signs, makes it possible to accurately determine the distance between these genes, and, therefore, to start building a genetic map, which is a diagram of the relative position of the genes that make up one chromosome.
7. What are chromosome maps for?
With the help of genetic maps, you can find out the location of animal and plant genes and information from them. This will help in the fight against various incurable diseases.
Hereditary and non-hereditary variability
1. Give definitions of concepts.
reaction rate- the ability of the genotype to form in ontogenesis, depending on environmental conditions, different phenotypes. It characterizes the share of participation of the environment in the implementation of the trait and determines the modification variability of the species.
Mutation- persistent (that is, one that can be inherited by the descendants of a given cell or organism) transformation of the genotype that occurs under the influence of the external or internal environment.
2. Fill in the table.
3. What limits depend on modification variability?
The limits of modification variability depend on the rate of reaction, which is genetically determined and inherited.
4. What do combinative and mutational variability have in common and how do they differ?
General: both types of variability are due to changes in the genetic material.
Differences: combinative variability occurs due to the recombination of genes during the fusion of gametes, and mutational variability is caused by the action of mutagens on the body.
5. Fill in the table.
Types of mutations
6. What is meant by mutagenic factors? Give relevant examples.
Mutagenic factors - influences leading to the occurrence of mutations.
It can be physical influences: ionizing radiation and ultraviolet radiation that damages DNA molecules; chemical substances that disrupt DNA structures and replication processes; viruses that insert their genes into the DNA of the host cell.
Inheritance of traits in humans. hereditary diseases in humans
1. Give definitions of concepts.
Genetic diseases- diseases caused by gene or chromosomal mutations.
Chromosomal diseases- diseases caused by a change in the number of chromosomes or their structure.
2. Fill in the table.
Inheritance of traits in humans
3. What is meant by sex-linked inheritance?
Sex-linked inheritance is the inheritance of traits whose genes are located on the sex chromosomes.
4. What traits are sex-linked in humans?
Sex-linked hemophilia and color blindness are inherited in humans.
5. Solve genetic problems for the inheritance of traits in humans, including sex-linked inheritance.
Task 1.
In humans, the gene for long eyelashes is dominant over the gene for short eyelashes. A woman with long eyelashes, whose father had short eyelashes, married men with short eyelashes. 1) How many types of gametes are formed in a woman? 2) How many types of gametes are formed in men? 3) What is the probability of the birth of a child with long eyelashes in this family (in %)? 4) How many different genotypes and how many phenotypes can be among the children of this married couple?
Decision
A - long eyelashes
a - short eyelashes.
The female is heterozygous (Aa) because her father had short eyelashes.
The male is homozygous (aa).
Answer:
1. 2
2. 1
3. 50
4. 2 genotypes (Aa) and 2 phenotypes (long and short eyelashes).
Task 2.
In humans, a free earlobe dominates over a closed one, and a smooth chin is recessive to a chin with a triangular fossa. These traits are inherited independently. From the marriage of a man with a closed earlobe and a triangular fossa on his chin and a woman with a free earlobe and a smooth chin, a son was born with a smooth chin and a closed earlobe. What is the probability of the birth in this family of a child with a smooth chin and free earlobe; with a triangular fossa on the chin (in %)?
Decision
A - free earlobe
a - not free earlobe
B - triangular fossa
c - smooth chin.
Since the couple had a child with homozygous traits (aavb), the genotype of the mother is Aavb, and the father is aaBv.
Let's write down the genotypes of the parents, the types of gametes and the crossing scheme.
Let's create a Punnett lattice.
Answer:
1. 25
2. 50.
Task 3.
In humans, the gene that causes hemophilia is recessive and is located on the X chromosome, and albinism is caused by autosomal recessive gene. Parents, normal in these characteristics, had a son with an albino and a hemophiliac. 1) What is the probability that their next son will show these two abnormal features? 2) What is the probability of having healthy daughters?
Decision:
X° - the presence of hemophilia (recessive), X - the absence of hemophilia.
A - normal skin color
a is an albino.
Parents' genotypes:
Mother - Х°ХАа
Father - HUAA.
Let's create a Punnett lattice.
Answer: the probability of manifestation of signs of albinism and hemophilia (genotype X ° Uaa) - in the next son - 6.25%. The probability of the birth of healthy daughters - (XXAA genotype) - 6.25%.
Task 4.
Hypertension in humans is determined by a dominant autosomal gene, while optic atrophy is caused by a sex-linked recessive gene. A woman with optic atrophy married a man with hypertension whose father also had hypertension and whose mother was healthy. 1) What is the probability that a child in this family will suffer from both anomalies (in %)? 2) What is the probability of having a healthy baby (in %)?
Decision.
X° - the presence of atrophy (recessive), X - the absence of atrophy.
A - hypertension
a - no hypertension.
Parents' genotypes:
Mother - X ° X ° aa (as she is ill with atrophy and without hypertension)
Father - XUAa (since he is not sick with atrophy and his father was with hypertension, and his mother is healthy).
Let's create a Punnett lattice.
Answer:
1. 25
2. 0 (only 25% of daughters will not have these deficiencies, but they will be carriers of atrophy and without hypertension).
