Justify the significance of hereditary variability in the evolution of the organic world. Heredity and variability are fundamental properties of living organisms

In our article we'll talk about the unique property of all living organisms, which ensured the emergence of a huge number of species of living beings. This is hereditary variation. What is it, what are its features and mechanism of implementation? You will now find answers to these and many other questions.

What does genetics study?

The relatively young science of genetics in the 19th century revealed to humanity many secrets of its origin and development. And the subject of its study is only two properties of living organisms: heredity and variability. Thanks to the first, the continuity of generations is ensured and the accurate transmission of genetic information is carried out over a number of generations. But variability ensures the emergence of new characteristics.

Variability value

Why does the body acquire these new characteristics? The answer is quite simple: for the possibility of adaptation. In the photo below you see representatives of several races of the same biological species- Reasonable Man. Their morphological differences at this stage naturally do not have any adaptive significance. But their distant ancestors had new features that helped them survive in difficult conditions. Yes, representatives Mongoloid race They have a narrow eye shape, since there were often dust storms in the steppes. And Negroids have dark skin as protection from the scorching rays of the sun.

Types of variability

Variability is the property of organisms to acquire new characteristics in the process of their historical and individual development. It comes in two types. This is modification and hereditary variability. They are united by a number of characteristics. For example, changes inevitably occur in external structure organisms. But in terms of the duration of existence of the modifications and the degree of action, they are completely different.

Modification variability

This type of variability is non-hereditary. It is not fixed in the genotype, is not permanent and occurs under the influence of changing conditions environment. A striking example modification variability can be served by the well-known experiment with a rabbit. A small section of his gray fur was shaved off. And ice was applied to the bare skin. After some time, wool grew in this place white, which was also shaved. But ice was not applied in this case. As a result, dark hair grew back in this area.

Hereditary variability

This type of variability is permanent, since it affects the structure of the genotype down to the level of DNA nucleotides. In this case, new characteristics are passed on to new generations. Hereditary variability, in turn, also comes in two types: combinative and mutational. The first occurs when a new combination of genetic material appears. Its simplest example is the fusion of gametes during sexual reproduction. As a result, the body, receiving half of the genetic information from the male and female organisms, acquires new characteristics.

The second type is mutational hereditary variability. It consists in the occurrence of sharp undirected changes in the genotype under the influence of various factors. They can be ionizing and ultraviolet radiation, high temperature, nitrogen-containing chemicals and others.

Depending on the level of structure of the genetic apparatus in which changes occur, several types of such hereditary modifications are distinguished. With genomic, the number of chromosomes in the total set changes. This leads to anatomical and morphological changes in the body. Thus, the appearance of the third chromosome in the 21st pair causes Down syndrome. With chromosomal mutations, a restructuring of this structure occurs. They are much less common than genomic ones. Parts of chromosomes may be duplicated or missing, twisted, or change their position. But gene mutations, also called point mutations, disrupt the sequence of monomers in the structure of nucleic acids.

Regardless of the type of mutation, all of them, as a rule, do not carry beneficial characteristics for the body. Therefore, a person learns to control them artificially. Thus, in selection, polyploidy is often used - a multiple increase in the number of chromosomes in a set. As a result, the plant becomes more powerful and produces large fruits in large quantities. You won’t surprise anyone with fig peach and other delicious plant hybrids. But they are the result of artificially carried out hereditary variability.

Hereditary variability in the process of evolution

The development of genetics has helped to make a significant step forward in the development of evolutionary teaching. The fact that humans and apes are distinguished by only one pair of chromosomes became significant evidence of Darwin's theory. In plants and animals in historical development, one can trace the inheritance of progressive traits that were transmitted and fixed in the genotype. For example, algae reached land due to the fact that the presence of mechanical and conductive tissues was fixed in the genotype. Each subsequent generation retained for itself only the necessary, useful traits, which were adjusted depending on living conditions and the environment. This is how the dominant species of plants and animals appeared, possessing the most progressive structural features.

So, hereditary variability is the ability of organisms to acquire new characteristics that are fixed in the genotype. Such changes are long-lasting, do not disappear when environmental conditions change, and are inherited.

There are 2 types of hereditary variability: mutational and combinative.

The basis of combinative variability is the formation of recombinations, i.e. such gene connections that the parents did not have. Phenotypically, this can manifest itself not only in the fact that parental characteristics are found in some offspring in other combinations, but also in the formation of new characteristics in the offspring that are absent in the parents. This happens when two or more non-allelic genes that differ between the parents influence the formation of the same trait.

The main sources of combinative variability are:

Independent segregation of homologous chromosomes in the first meiotic division;

Gene recombination, based on the phenomenon of chromosome crossing (recombination chromosomes, once in the zygote, cause the appearance of characteristics that are not typical for the parents);

Chance meeting of gametes during fertilization.

Mutation variability is based on mutations - persistent changes in the genotype that affect entire chromosomes, their parts or individual genes.

1) Types of mutations, according to the consequences of their influence on the body, are divided into beneficial, harmful and neutral.

2) According to the place of occurrence, mutations can be generative if they arise in germ cells: they can manifest themselves in the generation that develops from germ cells. Somatic mutations occur in somatic (non-reproductive) cells. Such mutations can be transmitted to descendants only through asexual or vegetative reproduction.

3) Depending on what part of the genotype they affect, mutations can be:

Genomic, leading to a multiple change in the number of chromosomes, for example, polyploidy;

Chromosomal, associated with a change in the structure of chromosomes, the addition of an extra section due to a crossover, a rotation of a certain section of chromosomes by 180°, or a change in the number of individual chromosomes. Thanks to chromosomal rearrangements, the evolution of the karyotype occurs, and individual mutants that arose as a result of such rearrangements may turn out to be more adapted to the conditions of existence, multiply and give rise to a new species;

Gene mutations are associated with changes in the sequence of nucleotides in a DNA molecule. This is the most common type of mutation.

4) According to the method of occurrence, mutations are divided into spontaneous and induced.

Spontaneous mutations occur naturally under the influence of mutagenic environmental factors without human intervention.

Induced mutations occur when mutagenic factors are directed to the body. Physical mutagens include various types of radiation, low and high temperatures; to chemical - various chemical compounds; to biological ones - viruses.

So, mutations are the main source of hereditary variability - a factor in the evolution of organisms. Thanks to mutations, new alleles appear (they are called mutant). However, most mutations are harmful to living beings, since they reduce their fitness and ability to produce offspring. Nature makes many mistakes, creating, thanks to mutations, many modified genotypes, but at the same time it always accurately and automatically selects those genotypes that give the phenotype most adapted to certain environmental conditions.

Thus, the mutation process is the main source of evolutionary change.

2. Give a general description of the class Dicotyledonous plants. What is the importance of dicotyledonous plants in nature and human life?

Class dicotyledons- plants whose seed embryo contains

two cotyledons.

Dicotyledonous class – 325 families.

Consider large families of dicotyledonous plants.

Trees. Herbaceous plants - eggplants, tomatoes, peppers, potatoes, nightshade, datura, henbane and many others. etc. SIGNIFICANCE IN NATURE: - plants of this class are producers in ecosystems, i.e. they photosynthesize organic matter ; - these plants are the beginning of all food chains; - these plants determine the type of biogeocenosis (birch forest, fireweed steppe); - This active participants

cycle of substances and water. SIGNIFICANCE IN HUMAN LIFE: - among plants of the Dicotyledonous class there are many cultivated plants , the organs of which are used for human food (Rosaceae family - cherry, apple, plum, raspberry, Asteraceae family - sunflower, Solanaceae family - tomato, potato, pepper, family Cruciferae - various varieties of cabbage, family Legumes - peas, soybeans , beans) - many plants are used for livestock feed; - in the production of natural threads (linen, cotton); - as cultural and decorative (acacia, roses); - medicinal (mustard, chamomile, nettle, thermopsis). Also among this class there are many spices; they are used to produce tobacco, coffee, tea, cocoa, dyes, ropes, ropes, paper, wooden utensils, furniture, musical instruments

; - the wood of some dicotyledons (oak, hornbeam, linden) is invaluable for construction.

Heredity and variability are properties of organisms. Genetics as a science Heredity
– the ability of organisms to transmit their characteristics and developmental characteristics to their offspring. Variability
– a variety of characteristics among representatives of a given species, as well as the ability of descendants to acquire differences from their parent forms. Genetics

– the science of the laws of heredity and variability.

2. Describe the contribution of scientists you know to the development of genetics as a science by filling out the table.

History of the development of genetics
The main method of genetics is hybridological. This is the crossing of certain organisms and analysis of their offspring. This method was used by G. Mendel.
Genealogical - the study of genealogies. Allows you to determine 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 - study under a microscope of the chromosome set - the number of chromosomes, features of their structure. Allows detection of chromosomal diseases.

4. What is the essence of the hybridological method of studying the inheritance of traits?
The hybridological method is one of the methods of genetics, a way of studying the hereditary properties of an organism by crossing it with a related form and subsequent analysis of the characteristics of the offspring.

5. Why can peas be considered a successful object for genetic research?
Pea species differ from each other in a small number of clearly distinguishable characteristics. Peas are easy to grow; in the Czech Republic they reproduce several times a year. In addition, in nature, peas are self-pollinators, but in experiments, self-pollination is easily prevented, and the researcher can easily pollinate the plant with the same pollen from another plant.

6. Inheritance of which pairs of traits in peas was studied by G. Mendel?
Mendel used 22 pure pea lines. Plants of these lines had very pronounced differences from each other: the shape of the seeds (round - wrinkled); seed color (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 pure line?
A pure line in genetics is a group of organisms that have some characteristics that are completely transmitted to the 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 containing two identical allelic genes.
Heterozygous organism– an organism containing two different allelic genes.

2. What is meant by monohybrid crossing?
Monohybrid crossing is the crossing of forms that differ from each other in one pair of alternative characters.

3. Formulate a rule for the uniformity of first-generation hybrids.
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 for this trait will be uniform.

4. Formulate the splitting rule.
When two descendants (hybrids) of the first generation are crossed with each other, in the second generation a split 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 gamete purity.
When formed, each of them includes only one of the two “elements of heredity” responsible for a given trait.

6. Using generally accepted symbols, draw up a diagram of monohybrid crossing.

Describe on in this example cytological basis of monohybrid crossing.
P is the parent generation, F1 is the first generation of descendants, F2 is the second generation of descendants, A is the gene responsible for the dominant trait, and A is the gene responsible for the recessive trait.
As a result of meiosis, the gametes of the parent individuals will contain one gene each, responsible for the inheritance of a certain trait (A or a). In the first generation, the 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 gene combinations will have the same phenotype (due to the presence of a dominant gene), while those with the fourth will have a different phenotype (recessive).

7. Solve the genetic problem of monohybrid crossing.
Task 1.
In watermelon, the green color of the fruit dominates over the striped color. By crossing a green-fruited variety with a striped-fruited one, first-generation hybrids with green-colored fruits were obtained. The hybrids were cross-pollinated and 172 second-generation hybrids were obtained. 1) How many types of gametes does a green-fruited plant produce? 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 color will there be in F2? 5) How many homozygous plants with green fruit color will there be in F2?
Solution
A – green color, and – striped color.
Since when crossing plants with green and striped fruits, plants with green fruit were obtained, we can conclude that the parent individuals were homozygous (AA and aa) (according to Mendel’s rule of uniformity of first-generation hybrids).
Let's draw up a crossing diagram.

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 long-haired cat crossed with a heterozygous short-haired cat produced 8 kittens. 1) How many types of gametes does a cat produce? 2) How many types of gametes does a cat produce? 3) How many phenotypically different kittens are there in the litter? 4) How many genotypically different kittens are there in the litter? 5) How many kittens in the litter have long hair?
Solution
A – short hair, and – long hair. Since the cat had long hair, she is homozygous, her genotype is aa. The cat has genotype Aa (heterozygous, short hair).
Let's draw up a crossing diagram.

Answers:
1. 2
2. 1
3. 4 with long and 4 with short
4. 4 with genotype Aa, and 4 with genotype aa
5. 4.

Multiple alleles. Analysis cross

1. Give definitions of concepts.
Phenotype– a set of all signs and properties of an organism that are revealed in the process of individual development in given 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?
The gene for any trait may have other “conditions” that cannot be called either dominant or 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 out the table.

Types of interaction of allelic genes

5. What is analytical crossing and what is its practical significance?
Test crossing is 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 crossing.
Task.

The white color of the phlox corolla dominates over the pink one. A plant with a white corolla was crossed with a plant with a pink color. 96 hybrid plants were obtained, of which 51 are white and 45 are pink. 1) What genotypes do the parent plants have? 2) How many types of gametes can a plant with a white corolla produce? 3) How many types of gametes can a plant with a pink corolla produce? 4) What phenotypic ratio can be expected in the F2 generation from crossing F1 hybrid plants with white flowers with each other?
Solution.
A – white color, and – pink color. The genotype of one plant A.. ​​is white, the second aa is pink.
Since in the first generation there is a 1:1 split (51:45), the genotype of the first plant is Aa.
Let's draw up a crossing diagram.

Answers:
1. Aa and aa.
2. 2
3. 1
4. 3 with a white corolla: 1 with a pink corolla.

Dihybrid cross

1. Give definitions of concepts.
Dihybrid cross– crossing of individuals in which differences from each other in two characteristics are taken into account.
Punnett grid is a table proposed by the English geneticist Reginald Punnett as a tool, which is a graphical record for determining 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 shape of seeds.
Yellow smooth (AABB) × Green wrinkled (AABB) =
R: AaBv×AaBv (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 characteristics.
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 coloring in cats dominates over fawn, and short hair dominates over long hair. Purebred Persian cats (black longhaired) were crossed with Siamese cats (fawn shorthaired). The resulting hybrids were crossed with each other. What is the probability of getting a purebred in F2 siamese kitten; a kitten phenotypically similar to a Persian; long-haired fawn kitten (express in parts)?
Solution:
A – black color, and – fawn.
B – short hair, B – long hair.

Let's create a Punnett lattice.

Answer:
1) 1/16
2) 3/16
3) 1/16.

Task 2.

In tomatoes round shape the fruits dominate over the pear-shaped ones, and the red coloring of the fruits dominates over the yellow ones. By crossing a heterozygous plant with a red color and pear-shaped fruits and a yellow-fruited plant with round fruits, 120 plants were obtained. 1) How many types of gametes does a heterozygous plant with red fruit color and pear-shaped form form? 2) How many different phenotypes resulted from such a cross? 3) How many different genotypes resulted from this crossing? 4) How many plants were obtained with a red color and a rounded fruit shape? 5) How many plants were obtained with a yellow color and a rounded fruit shape?
Solution
A – round shape, and – pear shape.
B – red color, c – yellow color.
Let's 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 representations about gene and genome

1. Give definitions of concepts.
Crossing over– the process of exchange of sections of homologous chromosomes during conjugation in prophase I of meiosis.
Chromosome map- this is a diagram of the relative position and relative distances between the genes of certain chromosomes located in the same linkage group.

2. In what case does the law of independent inheritance of characteristics 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 provisions of T. Morgan’s chromosomal theory of heredity.
A gene is a section of a chromosome.
Allelic genes (genes responsible for one trait) are located in strictly defined places (loci) of homologous chromosomes.
Genes are located linearly on chromosomes, that is, one after another.
During the formation of gametes, conjugation occurs between homologous chromosomes, as a result of which they can exchange allelic genes, that is, crossing over can occur.

4. Formulate Morgan's law.
Genes located on the same chromosome during meiosis end up in one 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 is the basis for compiling genetic maps of organisms?
Calculation of the frequency of crossing over between any two genes on the same chromosome responsible for various signs, makes it possible to accurately determine the distance between these genes, and therefore begin to build a genetic map, which is a diagram of the relative arrangement of genes that make up one chromosome.

7. Why are chromosome maps made?
Using genetic maps, you can find out the location of the genes of animals and plants and the information from them. This will help in the fight against various currently incurable diseases.

Hereditary and non-hereditary variability

1. Give definitions of concepts.

Norm of reaction– the ability of a genotype to form different phenotypes in ontogenesis, depending on environmental conditions. It characterizes the share of participation of the environment in the implementation of the trait and determines the modification variability of the species.
Mutation- a persistent (that is, one that can be inherited by the descendants of a given cell or organism) transformation of the genotype, occurring under the influence of the external or internal environment.
2. Fill out the table.

3. What determines the limits of modification variability?
The limits of modification variability depend on the reaction norm, 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 caused by 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 out the table.

Types of mutations

6. What is meant by mutagenic factors? Give relevant examples.
Mutagenic factors are influences that lead to the occurrence of mutations.
These can be physical influences: ionizing radiation and ultraviolet radiation, which damage DNA molecules; chemicals 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.
Gene diseases– diseases caused by gene or chromosomal mutations.
Chromosomal diseases– diseases caused by changes in the number of chromosomes or their structure.

2. Fill out 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 in humans are inherited in a sex-linked manner?
Hemophilia and color blindness are inherited in humans in a gender-linked manner.

5. Solve genetic problems on 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 does a woman produce? 2) How many types of gametes are produced in men? 3) What is the probability of having a child with long eyelashes in this family (in%)? 4) How many different genotypes and how many phenotypes can there be among the children of a given couple?
Solution
A – long eyelashes
a – short eyelashes.
The female is heterozygous (Aa), since the father had short eyelashes.
The man 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, the free earlobe is dominant over the non-free earlobe, and the smooth chin is recessive to the chin with a triangular fossa. These traits are inherited independently. From the marriage of a man with a loose earlobe and a triangular dimple on the chin and a woman with a loose earlobe and a smooth chin, a son was born with a smooth chin and a loose earlobe. What is the probability of having a child in this family with a smooth chin and a loose earlobe; with a triangular dimple on the chin (%)?
Solution
A – free earlobe
a – non-free earlobe
B – triangular fossa
c – smooth chin.
Since the couple had a child with homozygous characteristics (aabv), the genotype of the mother is Aavv, and the genotype of the father is aaBv.
Let's write down the genotypes of the parents, types of gametes and the crossing scheme.

Let's create a Punnett lattice.

Answer:
1. 25
2. 50.

Task 3.

In humans, the gene causing hemophilia is recessive and is located on the X chromosome, while albinism is caused by an autosomal recessive gene. Parents normal according to these characteristics gave birth to an albino and hemophilic son. 1) What is the probability that their next son will exhibit these two abnormal features? 2) What is the probability of having healthy daughters?
Solution:
X° - presence of hemophilia (recessive), X - absence of hemophilia.
A – normal skin color
a – albino.
Genotypes of parents:
Mother - X°HAa
Father - HUAa.
Let's create a Punnett lattice.

Answer: the probability of showing signs of albinism and hemophilia (genotype X°Uaa) in the next son is 6.25%. The probability of having healthy daughters is (XXAA genotype) – 6.25%.

Task 4.

Hypertension in humans is determined by a dominant autosomal gene, and 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 child (in%)?
Solution.
X° - presence of atrophy (recessive), X - absence of atrophy.
A – hypertension
a – no hypertension.
Genotypes of parents:
Mother - Х°Х°аa (since she is sick with atrophy and without hypertension)
Father - HUAa (since he is not sick with atrophy and his father had 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).

Variability called general property All living organisms acquire differences between individuals of the same species.

Charles Darwin identified the following main types of variability: definite (group, non-hereditary, modification), indefinite (individual, hereditary, mutation) and combined. Hereditary variability includes such changes in the characteristics of living beings that are associated with changes in (i.e. mutations) and are transmitted from generation to generation. The transfer of material from parents to offspring must occur very precisely, otherwise species cannot survive. However, sometimes quantitative or qualitative changes occur in the DNA, and the daughter cells receive distorted genes compared to the parental genes. Such errors in the hereditary material are passed on to the next generation and are called mutations. An organism that has acquired new properties as a result of mutations is called a mutant. Sometimes these changes are clearly visible phenotypically, for example, the absence of pigments in the skin and hair - albinism. But most often mutations are recessive and appear in the phenotype only when they are present in a homozygous state. The existence of hereditary variations was known. All of it follows from the doctrine of hereditary changes. Hereditary variability is a necessary prerequisite for natural and... However, at the time of Darwin there was still no experimental data on heredity and the laws of inheritance were not known. This did not make it possible to strictly distinguish different shapes variability.

Mutation theory was developed at the beginning of the twentieth century by the Dutch cytologist Hugo de Vries.

have a number of properties:
Mutations occur suddenly, and any part of the genotype can mutate.
Mutations are more often recessive and less often dominant.
Mutations can be harmful, neutral or beneficial for the body.
Mutations are passed on from generation to generation.

Mutations can occur under the influence of both external and internal influences.

Mutations are divided into several types: Point (gene) mutations
represent changes in individual genes. This can occur when one or more nucleotide pairs are replaced, dropped, or inserted in a DNA molecule. Chromosomal mutations
are changes in parts of a chromosome or entire chromosomes. Such mutations can occur as a result of deletion - the loss of part of a chromosome, duplication - doubling of any part of a chromosome, inversion - turning a part of a chromosome by 1800, translocation - tearing off a part of a chromosome and moving it to a new position, for example, joining to another chromosome. consist in changing the number of chromosomes in the haploid set. This can occur due to the loss of a chromosome from the genotype, or, conversely, an increase in the number of copies of any chromosome in the haploid set from one to two or more. A special case of genomic mutations is polyploidy - a multiple increase in the number of chromosomes. The concept of mutations was introduced into science by the Dutch botanist de Vries. In the plant primrose (evening primrose), he observed the appearance of sharp, abrupt deviations from the typical form, and these deviations turned out to be hereditary. Further studies on various objects - plants, animals, microorganisms - showed that the phenomenon of mutational variability is characteristic of all organisms.
The material basis of the genotype is chromosomes. Mutations are changes that occur in chromosomes under the influence of external or external factors. Mutational variability is newly emerging changes in the genotype, while combinations are new combinations of parental genes in the zygote. Mutations affect various aspects of the structure and functions of the body. For example, in Drosophila there are known mutational changes in the shape of the wings (up to their complete disappearance), body color, development of bristles on the body, eye shape, their color (red, yellow, white, cherry), as well as many physiological characteristics (life expectancy, fertility ).

They occur in different directions and in themselves are not adaptive, beneficial changes for the body.

Many mutations that occur are unfavorable for the body and can even cause its death. Most of these mutations are recessive.

Most mutants have reduced viability and are eliminated in the process natural selection. For the evolution of new breeds and varieties, those rare individuals that have favorable or neutral mutations are needed. The significance of mutations is that they create hereditary changes, which are the material for natural selection in nature. Mutations are also necessary for individuals with new properties that are valuable to humans. Artificial mutagenic factors are widely used to obtain new breeds of animals, plant varieties and strains of microorganisms.

Combinative variability also refers to hereditary forms of variability. It is caused by the rearrangement of genes during the process of gamete fusion and the formation of a zygote, i.e. during sexual intercourse.

LECTURE

SUBJECT:Heredity and variability

LECTURE PLAN:

Heredity and variability are properties of organisms. Genetics as a science

Variability

1. Hereditary variability

   Non-hereditary variability

1. Heredity

Development organic world, largely depends on factors such as heredity and variability.Heredity call the general property of all organisms to store and transmit their characteristics to offspring. Thanks to heredity, the specific qualities of each biological species are preserved from generation to generation.

The connection between parents and offspring in organisms occurs mainly through reproduction. Although the offspring are like parents and ancestors, they are not theirs. an exact copy. The mechanism of heredity has long interested humanity. In 1866 G. Mendel expressed the opinion that the characteristics of organisms are determined by heritable units, which he called “elements”. Later they began to be calledhereditary factors and finallygenes . Genes are located on chromosomes and they are passed on from one generation to the next.

Despite the fact that much is now known about chromosomes and the structure of DNA, give precise definition gene is still difficult. As a result of studying the nature of a gene, it can be defined as a unit of recombination, mutation and function.Gene is a factor of heredity, a functionally indivisible unit of genetic material in the form of a section of a nucleic acid molecule (DNA or RNA).It encodes a specific protein structure, t-RNA or r-RNA molecules, or interacts with biologically active substances (for example, enzymes). A gene is an integral functional unit, and any violation of its structure changes the information encoded in it or leads to its loss.

As a result of heredity, the body receives a set of genes from its parents, which is commonly calledgenotype . The genome of eukaryotes is more complex than that of prokaryotes because it has large quantity nuclear DNA, structural and regulatory genes. In addition to the hereditary material located in the nucleus, there is alsocytoplasmic inheritance , orextranuclear . It lies in the ability of certain cytoplasmic structures to store and transmit to descendants part of the hereditary information of the parents. Although the leading role in the inheritance of most traits of an organism belongs to nuclear genes, the role of cytoplasmic inheritance is also significant. It is associated with two types of geneticphenomena:

Inheritance of traits that are encodedextranuclear genes located in certain organelles (mitochondria, plastids);

The manifestation in descendants of traits predetermined by nuclear genes, the formation of which is influenced byegg cytoplasm .

The existence of genes in organelles (mitochondria, plastids) capable of self-duplication became known at the beginning of the twentieth century. while studying green and colorless plastids in some flowering plants with mosaic leaf colors. Extranuclear genes, interacting with nuclear ones, influence the formation of the trait. For example, cytoplasmic heredity associated with plastid genes affects such a trait as variegation in plants (begonia, snapdragon, etc.). And this trait is transmitted through the maternal line.

The reason for variegation is the loss of the ability of some plastids to form the pigment chlorophyll. After cell division with colorless plastids, white spots appear in the leaves, which alternate with green areas. The transmission of this trait through the maternal line is explained by the fact that during the formation of gametes, plastids reach the eggs, and not the sperm. When new plastids are formed, green plastids give rise to green ones, and colorless plastids give rise to colorless ones. During cell division, plastids are randomly distributed, resulting in cells with colorless, green, or both plastids..

The phenomenon of cytoplasmic inheritance associated with mitochondrial genes can be observed in yeast. In these microorganisms, genes were found in the mitochondria that determine the absence or presence of respiratory enzymes, as well as resistance to certain antibiotics. The influence of the nuclear genes of the mother's body through the cytoplasm of the egg on the formation of characteristics can be traced using the example of the pond snail. This freshwater mollusk has forms with in different directions twisting the shell - left or right. The allele that determines the twisting of the shell to the right dominates the left-handed allele, but this trait is determined by the genes of the maternal individual. For example, individuals homozygous for a recessive gene (left-handed) may have a right-handed shell if the maternal organism had a dominant allele.

2. Variability

Variabilityname the entire set of differences in one or another characteristic between organisms that belong to the same population or species. There are two main forms of variability:hereditaryAndnon-hereditary.

2.1. Hereditary variability

Hereditary variability is the variability that is transmitted from parents to offspring, i.e. inherited. This variability is associated with changes in genetic material caused by mutations. That is why hereditary variability is also calledgenotypic , genetic ormutational .

Mutation is a change in chromosomes that occurs under the influence of environmental factors. The concept of mutations was introduced into science by the Dutch botanist Hugo Frieze. He also formulatedmutation theory , a number of provisions of which belong to the famous Russian botanist S.I. Korzhinsky.

Basic provisions of modern mutation theory :

Mutations occur suddenly, spasmodically and appear in the form of discrete symptoms;

Mutations are not lost and are passed on from generation to generation;

Mutations manifest themselves in different ways and can be dominant or recessive, beneficial or harmful, differ in the strength of their effect on the body, cause minor changes in the functioning of the body or affect vital signs and be lethal;

The probability of detecting mutations depends on the number of individuals examined;

Mutations can occur repeatedly;

Mutations can be caused by the influence of potent physical or chemical agents on the body, but the appearance of a particular mutation is not related to the type of agent;

Mutations are always spontaneous, independent of one another, and do not have a group orientation. Any part of a chromosome can mutate.

Mutational variability, in contrast to modification, is an important source of evolutionary transformations. Thanks to genetic variability, organisms with new properties and characteristics are formed, and a high level of phenotypic variability is also maintained.

Depending on the nature of the influence on the viability of organisms, they are distinguishedlethal , sublethal Andneutral mutations. Lethal, as a rule, entail the death of organisms even before birth or before the onset of sexual maturity. Sublethal - reduce viability, leading to the death of some (from 10 to 50%). Neutral mutations under normal living conditions for organisms do not affect their viability. And in some cases, such mutations can even become useful, especially when the living conditions of the organism change.

Based on the nature of hereditary changes in genetic material, three types of mutations are distinguished: gene, chromosomal, and genomic.

Genetic ( point ) mutations – are qualitative changes in individual genes. These mutations occur at the level of the primary DNA strand and lead to disruption of the amino acid sequence in proteins. Such changes can have negative consequences for the body. After all, the amino acid sequence in each protein is strictly specific, and replacing even one of them can lead to disruption of the spatial structure of the protein and, accordingly, functions.

The most common case of a point mutation is the replacement of a nucleotide pair from GA to GC or vice versa. If these changes occur within structural genes, then as a result, instead of the AGA triplet, the AHC triplet may appear in the polypeptide chain, respectively, instead of a negatively charged amino acidarginine will be an uncharged amino acidserine. Such a mutation can lead to a change in the charge of the protein, disruption of its conformation, and if it is an enzyme, then to a decrease in the rate of the chemical reaction that it catalyzes. As a result, disruptions in the metabolism of the entire body may begin.

Substitutions can also be neutral, for example, substitutions of amino acids with the same properties. Stop codon mutations or mutations of loss or insertion of one of the nucleotides lead to extremely negative consequences. As a result, part or all of the sequence of triplets is changed, which contributes to a serious violation of the amino acid structure of the protein and this is almost always incompatible with the normal functioning of the body.

represent changes in individual genes. This can occur when one or more nucleotide pairs are replaced, dropped, or inserted in a DNA molecule. – mutations associated with visible transformations of chromosomes. This can be a movement of one part of a chromosome to another, a rotation of a section of a chromosome by 180°, the insertion of extra parts of a chromosome, or, conversely, the loss of some sections. In most cases, chromosomal rearrangements do not occur without consequences for the body. Most often they lead to fatal outcome even at very early stages of embryonic development. If chromosomal changes do not affect genes that are responsible for important functions of the body, then they usually lead to meiotic disorders, and therefore to infertility of the individual. However, there are also completely neutral chromosomal mutations(chromosomal polymorphisms).

Genomic mutations associated with changes in the number of chromosomes. They are caused by gross violations of meiosis. One type of chromosomal mutation isaneuploidy- an increase in homologous chromosomes by one or more or, on the contrary, a deficiency, most often of one chromosome. Typically in animals, such disorders are incompatible with the normal functioning of the body and lead either to death in the early stages or to numerous developmental disorders. The hereditary human disease, the so-called Down syndrome, is caused by the appearance of a third additional chromosome in the 21st pair. And the appearance of the third chromosome in the 15th pair causes another hereditary human anomaly - polydactyly - the appearance of a sixth finger on the limbs.

Genomic mutations associated with a multiple increase in the number of chromosomes are calledpolyploidy (from Greekpolyploethia many, large number). If the number of chromosome sets increases by one, then it is a triploid, if by two, it is a tetraploid, etc. The greatest increase in the number of chromosome sets found in organisms is those with a tenfold chromosome set.

Polyploidy helps to increase the size of the body, accelerates vital processes, and can cause disturbances in the process of reproduction. This is especially true for polyploid forms with an unpaired set of chromosomes, which can reproduce only by parthenogenesis or vegetatively.

Polyploidy is very common in nature. For the most part, it is represented by paroploid (tetra- or octoploid) forms in which meiosis occurs normally. There are a lot of polyploid species among plants and much fewer among animals. Quite often they are found among invertebrates (crustaceans, mollusks, worms). There are polyploids among vertebrates. In fish, for example, there are even entire families (sturgeons) and orders (salmonids), the species of which are exclusively polyploid. Polypoids occur less frequently in amphibians and reptiles, and in birds and mammals such individuals die on early stages development.

Somatic mutations – mutations that occur only in individual somatic cells. In organisms that reproduce sexually (most animals), such mutations are not inherited. It’s a different matter in plants - vegetative propagation allows you to preserve the change that has arisen and make it hereditary.

Most mutations that occur in the body, as a rule, are recessive, and the wild type (the so-called common phenotype characteristic of individuals living in natural conditions) is dominant. For example,albinism(from lat.albus– white) is a recessive trait that manifests itself in the homozygous (aa) state as the absence of pigment in the skin, hair, and iris of the eyes. As it turned out, the enzyme tyrosinase, which catalyzes the formation of the melanin pigment, does not function in albino individuals. Heterozygous individuals (Aa) have a wild color.

Dominant mutations also appear in the heterozygous state, but they occur much less frequently than recessive ones. The consequence of such mutations is, for example, the majority of cases of the appearance of melanistic animals, in which, unlike non-mutated individuals, a lot of melanin is synthesized. Usually such organisms have a darker color.

One more important factor genetic variability isrecombination (from lat.re– a prefix that indicates a repeated action andcombinare,– connection) – redistribution of genetic material in the offspring. The main reasons for gene recombination are:

The combination of gametes from different parents in the case of random crossing in animals and cross-pollination in plants;

Independent distribution of chromosomes after the first meiotic division;

Crossing over is the exchange of sections of homologous chromosomes during conjugation in metaphaseMeiosis I.

As a result of sexual reproduction, recombination leads to the formation of offspring with a wide variety of genotypic combinations. As a result, it is impossible to find two genetically identical individuals in one population. Recombination plays an important role in the evolution of organisms. Its properties are used in the process of breeding new varieties of plants and animal breeds.

2.2. Non-hereditary variability

The development of an organism's phenotype occurs through the interaction of its hereditary basis - genotype - with environmental conditions. Signs of an organism vary to varying degrees under the influence of various environmental factors. Some of them are very plastic and changeable, others are less changeable, and others practically do not change under the influence of environmental conditions. For example, the milk yield of cattle largely depends on housing conditions (feeding, care). While milk fat content is largely breed dependent and difficult to change, although some results can be achieved by changing the diet. An even more permanent feature is the suit. Under all possible conditions, it remains almost unchanged.

Modification (from lat.modulus– measure, type andfacies- shape, appearance)variability – These are changes in the characteristics of an organism (its phenotype) caused by changes in environmental conditions and not associated with changes in the genotype.Due to the fact that modification variability is not associated with changes in the genotype, it is not inherited.

Actually modificationchanges (modifications)– these are the reactions of organisms to changes in the intensity of the action of certain environmental factors. They are the same for all genotypes of closely related organisms. For example, all arrowhead plants immersed in water develop long and thin leaves, while those growing on dry land have arrow-shaped leaves. Arrowhead plants that are partially submerged in water produce both types of leaves.

In the diurnal butterfly, the variable wing color depends on the temperature at which the pupae developed. From those pupae that overwintered, butterflies emerge with a brick-red color, and from those that developed in the summer in conditions of elevated temperatures, butterflies emerge with a black background of wings. The degree of severity of modifications directly depends on the intensity and duration of action of a certain factor on the body. Thus, in the small brine shrimp, the degree of hairiness of the rear part of the abdomen depends on the salinity of the water: the lower the salt concentration, the greater it is.

As numerous studies have shown, modifications can disappear during the life of one individual if the action of the factor that caused them ceases. For example, a tan acquired by a person in the summer gradually disappears during the autumn-winter period. If an arrowhead plant is transplanted from water to dry land, the new leaves will not have an elongated, but an arrow-shaped shape. The resulting modifications can persist throughout the life of the individual, especially those that arose in the early stages of individual development. But they are not passed on to descendants. For example, curvature of the bones of the lower extremities as a result of rickets persists throughout life. But to parents who suffered from rickets in childhood, children are born normal if during their development they receive the required amount of vitamin D. Another example of modifications that persist throughout life is the differentiation of honey bee larvae into queens and workers. The larvae, which develop in special large cells of honeycombs and feed only on “royal jelly”, which is produced by the special glands of worker bees, develop into queens. And those who are fed with beebread (a mixture of honey and pollen) subsequently become workers - underdeveloped females, incapable of reproduction. Therefore, differentiation of female honey bee larvae depends on the food they receive during their development. If at the early stages of development the larvae are swapped, from which the queen and worker bee should subsequently develop, then the nature of their nutrition and subsequent differentiation will change accordingly. However, at later stages of development this becomes impossible.

Modification variability plays an exceptional role in the life of organisms, ensuring their adaptability to changes in environmental conditions. Thus, changing the shape of arrowhead leaves from arrow-shaped to ribbon-shaped (linear) when this plant is immersed in water protects it from damage by the current. The change to a thicker coat of mammals during autumn molting provides protection from low temperatures, and a human tan provides protection from the harmful effects of solar radiation. All this gives reason to believe that such modifications arose in the process historical development species as certain adaptive reactions to changing environmental conditions that organisms constantly encounter. However, not all modifications are adaptive. For example, if you shade the lower part of a potato stem, above-ground tubers will begin to form on it. Modifications devoid of adaptive significance arise when organisms find themselves in unusual conditions that their ancestors did not have to encounter.

Modification variability is subject to certainstatistical patterns . In particular, any characteristic can vary only within certain limits. Such limits of modification variability (from min to max) of traits are predetermined by the genotype of the organism and are calledreaction norm . Consequently, a specific allelic gene does not predetermine the development of a specific state of the trait it encodes, but only the limits within which it can vary depending on the intensity of the action of certain environmental factors. Among the characters there are those whose different states are almost entirely determined by the genotype (for example, the location of the eyes, the number of fingers on the limbs, blood type, the pattern of leaf venation, etc.). But the degree of manifestation of the states of other characteristics (height and weight of organisms, the size of the puff plate, etc.) is significantly influenced by environmental conditions. For example, the development of fur colors of some animals (for example, ermine rabbits, Siamese cats) depends on temperature. If you shave an area of ​​the body covered with white hair in such animals and apply ice to it, then in low temperature conditions black hair will grow in this area.

The reaction norm for different characteristics has its own limits. Signs that determine the viability of organisms (for example, the relative position of internal organs), and for signs that do not carry important life significance, it can be much wider (body weight, height, hair color).

Usually a single manifestation of a trait is calledoption . To study the variability of a particular trait, i.e. option, make upvariational (from lat.variatio –change)row – a sequence of quantitative indicators of manifestations of states of a certain characteristic (variant), arranged in ascending or descending order.

The length of the variation series indicates the scope of the modification variability (reaction norm). It is predetermined by the genotype of the organism, but depends on environmental conditions: the more stable they are, the shorter the variation series will be, and vice versa. If you trace the distribution of individual options within the variation series, you will notice that the largest number of them are located in its middle part, i.e. they have the average value of this characteristic.

This distribution is explained by the fact that the minimum and maximum values ​​of trait development are formed when the majority of environmental factors act in one direction: the most or least favorable. But the body, as a rule, feels their different influences: some factors contribute to the development of the trait, while others, on the contrary, inhibit it. That is why the degree of development of a certain trait in most individuals of the same species is averaged. Yes, most people have average height, and only a small part of them are giants or dwarfs. The distribution of variants within a variation series can be graphically depicted in the form of a variation curve.Variation curve – this is a graphical representation of the dependence of possible variants of a trait on the frequency of occurrence.Using a variation curve, you can establish the average indicators and reaction norm of a certain trait.

GENERALIZATION

The manifestation of the phenotype of each organism depends on heredity and variability. Thanks to heredity, an individual receives a genetic set from its parental forms, thus preserving the specific characteristics of each species, and variability violates this pattern - thanks to variability, it is impossible to meet two genetically identical individuals in the world.

There are two types of variability: non-hereditary (phenotypic, modification) and hereditary (genotypic, genetic). Factors of genetic variability are mutations and recombinations of genetic material. Therefore, hereditary variability is also called mutational. Modifying variability is caused by the body's reactions to environmental factors. And since the conditions for the formation of each organism are largely different, individuals, even if they are representatives of the same species, have their own unique phenotype.

Heredity and variability play an important role in the evolution of organisms. Their properties are also used in the process of breeding new varieties of plants and animal breeds.

QUESTIONS FOR CONTROL

1. What is a gene from a biochemical and genetic point of view?

2. Why are heredity and variability called alternative phenomena? Define heredity and variability.

3. What is cytoplasmic inheritance and what causes it?

4. What are mutations? What types of mutations do you know?

5. What are aneuploidy and polyploidy?

6. Why do mutations associated with a multiple decrease in the chromosome set negatively affect the viability of organisms compared to those caused by a multiple increase in the genome?

7. Are most mutations recessive or dominant?

8. What is the difference between modification and mutational variability?

9. What is called the reaction norm of modification variability?

10. What is included in the statistical processing of modification variability data?