Patterns of variability. non-hereditary (modification) variability. reaction norm. hereditary variability: mutational, combinative. types of mutations and their causes. the significance of variability in the life of organisms and in evolution

Variability- the ability of organisms to acquire new characteristics. This leads to a variety of properties and characteristics in individuals varying degrees kinship. Changes in phenotype can be associated either with environmental influences on gene expression or with changes in the genetic material itself. Depending on this, a distinction is made between non-hereditary (modification) variability and hereditary (genetic) variability.

Non-hereditary (modification) variability

Non-hereditary variability

• affects only the phenotype (the genotype does not change);
• not inherited;
• is adaptive in nature to environmental conditions.

The basis of modification variability is the fact that it is not the trait itself that is inherited, but only the ability to develop it. Depending on environmental conditions, the trait may manifest itself to varying degrees. The limits of variation (variability) of a characteristic are called reaction norm. The reaction norm depends on genes, and environmental conditions determine which option within this reaction norm is realized in a given case.

Reaction norms various signs are not the same. As a rule, qualitative characteristics have a narrow reaction norm (for example, blood type), while quantitative characteristics have a wide reaction norm (for example, height and body weight).
Give objective assessment a variable characteristic is possible only by analyzing a large number of individuals. To evaluate a characteristic, a variation curve is constructed and the average value of the characteristic is found. The values ​​of the attribute size form a continuous series around average size. The most common are individuals with average development values ​​of the trait, and what more sign deviates from the average value, the fewer individuals possess it.
As noted, a genotype is not a mechanical set of genes, that is, if there is a gene, then the trait must necessarily develop. From the interaction of genes in the genotype and the influence environment the degree of expression and frequency of manifestation of individual genes in the phenotype depend.

Expressiveness- degree of manifestation of a varying trait. Expressiveness characterizes the degree of deviation of a trait from its average value.

Penetrance- the degree of penetration of genes into a trait.

Measured as a percentage of the number of individuals carrying this sign, to the number of individuals carrying a gene that can potentially be realized into a trait. The penetrance of a gene can be complete (100%) if this trait is observed in all individuals, and incomplete if it appears only in part of the population.

Hereditary (genotypic) variability

Hereditary variability

• affects the genotype;
• is inherited;
• is random.

Hereditary variability can be combinative and mutational.
Combinative variability arises as a result of the formation in descendants of new combinations of already existing genes during sexual reproduction.
The sources of combinative variability are

1. independent divergence of homologous chromosomes in the first-meiotic division and their random combination during fertilization;
2. recombination of genes as a result of crossing over.

Thus, in the process of combinative variability, the molecular structure of genes does not change, but new combinations of alleles in genotypes lead to the appearance of organisms with new phenotypes.
Mutational variability occurs as a result of mutations. Mutations - qualitative or quantitative changes in the DNA of organisms, leading to changes in their genotype.

Mutations are characterized by the following properties:

• these are sudden abrupt changes in heredity;
• these are persistent changes in hereditary material (passed on by inheritance);
• these are qualitative (discrete) changes (they do not form a continuous series around the average value);
• these are undirected changes (random in nature);
• can be beneficial (very rare), harmful (most mutations) and neutral (indifferent to the given conditions of existence of the organism);
• can be repeated (similar mutations can occur repeatedly).

There are several principles of classification mutations:

• by change in genotype: a) genetic; b) chromosomal; c) genomic;
• by changes in phenotype: a) morphological; b) biochemical; c) physiological; d) lethal, etc.;
• in relation to the generative path: a) somatic; b) generative;
• according to the manifestation of the mutation in a heterozygote: a) dominant; b) recessive;
• by localization in the cell: a) nuclear, b) cytoplasmic;
• by reasons of occurrence: a) spontaneous, b) induced.

Generative mutations - mutations of germ cells (transmitted during sexual reproduction). Somatic mutations - mutations of somatic cells (transmitted during vegetative propagation).
Gene (point) mutations associated with changes in the nucleotide sequence of the DNA of one gene. There are two mechanisms of gene mutations: the replacement of one nucleotide with another and the loss or insertion of one of them. As a result, a change occurs in RNA transcription and protein synthesis, which causes the appearance of new or changed characteristics. The insertion and deletion of nucleotides lead to more significant consequences than their replacement, since triplets are shifted and not one amino acid is changed, but the entire further sequence of amino acids.

Chromosomal mutations are associated with the movement of chromosome sections. Changes in the structure of chromosomes may involve sections of one chromosome or different, non-homologous chromosomes. Distinguish different types chromosomal mutations:

The mechanism of chromosomal mutations is the formation of chromosome breaks under the influence of mutagens with the possible loss of some fragments and the reunification of parts of the chromosome in a different order compared to the original chromosome.
Genomic mutations associated with changes in the number of chromosomes. There are polyploidy and heteroploidy. Polyploidy- an increase in the number of chromosomes, a multiple of the haploid set (3n - triploidy, 4n - tetraploidy, etc.). The reasons for polyploidy can be different: the formation of gametes with an unreduced number of chromosomes during meiosis; fusion of somatic cells or their nuclei; duplication of chromosomes without subsequent cell division. Polyploidy is common in plants and rare in animals. Heteroploidy- a change in the number of chromosomes that is not a multiple of the haploid set (2n-1 - monosomy; 2n+1 - trisomy; polysomy, etc. on individual chromosomes). The cause of heteroploidy is the nondisjunction of individual homologous chromosomes during gametogenesis, resulting in the appearance of gametes in which some chromosomes are either absent or present in double numbers. Changes in the number of chromosomes often cause developmental disorders and even lethality. For example, Down's disease is caused by the presence of three chromosomes 21 pairs.

Mutagenic factors

Mutagenic factors can be divided into two groups. On the one hand, mutations can occur spontaneously due to errors during DNA replication, repair and recombination. On the other hand, they can be caused external reasons- mutagens.
Mutagens - external (environmental) factors causing mutation. They are divided into physical (ultraviolet, x-rays and gamma rays, increased or low temperature), chemical (benzopyrene, nitrous acid), biological (some viruses).
Currently, as a result production activities environmental pollution with mutagens increases. As a result, the number of mutations is growing both among people and among other living organisms. The vast majority of mutations are harmful, that is, they increase morbidity and mortality.
Often mutagens are both carcinogens - factors, causing development malignant tumors.

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

Mutations- changes that have occurred in the genetic information of a cell; these changes can have different scales and are divided into types.

Types of mutations

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

Chromosomal mutations- changes affecting areas within one chromosome.

Gene mutations- changes that occur within one gene.

As a result of genomic mutations, the number of chromosomes within the genome changes. This is due to disruption of the spindle function, so homologous chromosomes do not diverge to different poles of the cell.

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

Rice. 1. Genomic mutation

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

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

Rice. 2. Higher plants, fungi, algae

Such organisms are called polyploid; polyploid plants can contain from three to one hundred haploid sets. Unlike most mutations, polyploidy most often benefits the body; polyploid individuals are larger than usual. Many cultivated plant varieties are polyploid (Fig. 3).

Rice. 3. Polyploid crops

Humans can induce polyploidy artificially by exposing plants to colchicine (Fig. 4).

Rice. 4. Colchicine

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

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

Rice. 5. Down syndrome

A type of genomic mutation is also the division of one chromosome into two and the fusion of two chromosomes into one.

Chromosomal mutations are divided into types:

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

Rice. 6. Deletion

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

Rice. 7. Duplication

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

Rice. 8. Inversion

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

Rice. 9. Translocation

Changes with deletions and duplications total genetic material, the degree of phenotypic manifestation of these mutations depends on the size of the altered areas, as well as on how important genes are in these areas.

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

Bibliography

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

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

Homework

1. Where are genomic mutations most common?
2. What are polyploid organisms?
3. What types of chromosomal mutations are divided into?

Mutations

1. What cells are called polyploid
A) containing more than two sets of homologous chromosomes
B) obtained as a result of hybridization
B) containing multiallelic genes
D) obtained from crossing several pure lines

2. Rotating a section of a chromosome by 180 degrees refers to mutations
A) genomic
B) genetic
B) chromosomal
D) point

3. Somatic mutations are passed on to offspring
A) plants during vegetative propagation
B) animals during sexual reproduction
B) animals that reproduce parthenogenetically
D) plants with double fertilization

4. The causes of gene mutations are disorders that occur when
A) DNA reduplication
B) biosynthesis of carbohydrates
B) formation of ATP
D) synthesis of amino acids

5. Polyploid organisms arise as a result
A) genomic mutations
B) modification variability
B) gene mutations
D) combinative variability

6. What type of mutations are changes in the DNA structure in mitochondria?
A) genomic
B) chromosomal
B) cytoplasmic
D) combinative

7. It is possible for breeders to obtain polyploid wheat varieties due to mutation
A) cytoplasmic
B) genetic
B) chromosomal
D) genomic

8. Loss of a chromosome section, in contrast to the crossing of chromatids in meiosis, is
A) conjugation
B) mutation
B) replication
D) crossing over

9. Variegation of night beauty and snapdragon is determined by variability
A) combinative
B) chromosomal
B) cytoplasmic
D) genetic

10. Polyploid wheat varieties are the result of variability
A) chromosomal
B) modification
B) genetic
D) genomic

12. An animal in whose offspring a trait due to a somatic mutation may appear
A) hydra
B) wolf
B) hedgehog
D) otter

13. A change in the sequence of nucleotides in a DNA molecule is a mutation
A) genetic
B) genomic
B) chromosomal
D) autosomal

14. The loss of four nucleotides in DNA is
A) modification change
B) gene mutation
B) chromosomal mutation
D) genomic mutation

15. Polyploidy is one of the forms of variability
A) modification
B) mutational
B) combinative
D) correlative

16. Which human disease is the result of a gene mutation?
A) acquired immunodeficiency syndrome
B) flu
B) sickle cell anemia
D) hepatitis

17. Down's disease is associated with the appearance of an extra 21st pair of chromosomes in the human genotype, therefore such a change is called
A) somatic mutation
B) genomic mutation
B) polyploidy
D) heterosis

18. Mutations associated with the exchange of sections of non-homologous chromosomes are classified as
A) chromosomal
B) genomic
B) point
D) genetic

19. Variability of organisms caused by a multiple increase in sets of chromosomes in cells is
A) gene mutation
B) polyploidy
B) heterosis
D) point mutation

20. You can increase the frequency of mutations in a population
A) action x-rays per individual
B) interspecific crosses
B) by crossing pure lines
D) crossing heterozygous organisms

21. Recessive gene mutations change
A) sequence of stages of individual development
B) composition of triplets in a DNA section
B) set of chromosomes in somatic cells
D) structure of autosomes

22. Somatic mutations
A) are caused by changes in autosomes in germ cells
B) associated with sex-linked inheritance
C) transmitted to offspring in plants during vegetative propagation
D) arise in gametes in animals

23. Down syndrome is the result of a mutation
1) genomic
2) cytoplasmic
3) chromosomal
4) recessive

24. The birth of a child with Down syndrome is an example of variability
A) modification
B) combinative
B) cytoplasmic
D) genomic

25. What cells are called polyploid?
A) having a multiple increased number of chromosomes
B) containing dominant genes
B) obtained as a result of hybridization
D) obtained from crossing pure lines

26. Somatic mutations in humans
A) are not inherited by offspring
B) increase metabolic rate
C) serve as the basis for adaptation
D) arise in gametes

27. Somatic mutations in vertebrates
A) are formed in gametes
B) are passed on to the next generation
C) arise in the cells of body organs
D) caused by metabolic disorders

28. Mutational variability is due to
A) recombination of genes in homologous chromosomes
B) a change in the sequence of nucleotides in DNA
C) a change in the characteristic within the normal range of reaction
D) the formation of hybrid offspring

Hereditary (genotypic) variability manifests itself in a change in the genotype of an individual, therefore it is transmitted through sexual reproduction to descendants.

Hereditary variability is due to the occurrence of different types of mutations and their combinations in subsequent crosses. In each sufficiently long-existing population of individuals, various mutations arise spontaneously and undirectedly, which are subsequently combined more or less randomly with existing gene variants.

Types of hereditary variability:

• combinative: caused by the recombination of genes as a result of meiosis and fertilization;
• mutational: caused by the occurrence of mutations.

Combinative variability

Combinative called variability, which is based on education recombinations, i.e., such combinations of genes that the parents did not have.

The basis of combinative variability is the sexual reproduction of organisms, as a result of which a huge variety of genotypes arises. Three processes serve as virtually unlimited sources of genetic variation during sexual reproduction in eukaryotes:

1. Independent segregation of homologous chromosomes in anaphase of the first meiotic division. It is the independent combination of chromosomes during meiosis that is the basis of Mendel's third law. The appearance of green smooth and yellow wrinkled pea seeds in the second generation from crossing plants with yellow smooth and green wrinkled seeds is an example of combinative variability.
2. Mutual exchange of sections of homologous chromosomes, or crossing over, in the prophase of the first division of meiosis. It creates new linkage groups, i.e. it serves as an important source of genetic recombination of alleles. Recombinant chromosomes, once in the zygote, contribute to the appearance of characteristics that are atypical for each of the parents.
3. Random combination of gametes during fertilization.

These sources of combinative variation act independently and simultaneously, ensuring constant “shuffling” of genes, which leads to the emergence of organisms with a different genotype and phenotype (the genes themselves do not change). However, new gene combinations break down quite easily when passed on from generation to generation. Combinative variability is the most important source of all the colossal hereditary diversity characteristic of living organisms. However, as a rule, it does not generate stable changes in the genotype, which, according to evolutionary theory, are necessary for the emergence of new species. Stable, long-lived changes arise as a result of mutations.

Mutational variability

Mutation is a stable and non-directional change in the genome.

The mutation persists indefinitely over a number of generations.

The significance of mutations in evolution is enormous - thanks to them, new gene variants arise. They say that mutations are the raw material of evolution. Mutations are individual (each mutation in a single DNA molecule occurs randomly) and non-directional.

Mutations may or may not lead to changes in the characteristics and properties of the organism.

Mutations occur constantly throughout human ontogenesis. The earlier in the development of an organism a specific mutation occurs, the greater the impact it can have on the development of the organism (Fig. 1).

Rice. 1. Impact of mutations in different periods ontogeny

Mutations are divided into:

• neutral;
• harmful;
• useful.

Modern geneticists believe that most newly emerging mutations neutral, that is, they do not affect the fitness of the organism in any way. Neutral mutations occur in intergenic regions - introns (sections of DNA that do not code for proteins); either this synonymous mutations in the coding part of the gene - mutations that lead to the appearance of a codon designating the same amino acid (this is possible due to the degeneracy of the genetic code).

The next most common are harmful mutations. The harmful effect of mutations is explained by the fact that the changes concern hereditary traits that most often have adaptive significance, that is, traits that are useful in given environmental conditions.

Only a small part of mutations increases the fitness of the organism, that is, it is useful(“breaking does not build”).

However, the harmfulness and usefulness of mutations are relative concepts, since what is useful (harmful) under given conditions may have the opposite effect when environmental conditions change. That is why mutations are the material for evolution.

Mutagenesis- the process of mutation occurrence.

Mutations can appear in both somatic and germ cells (Fig. 2).

Rice. 2. Result of mutations

Despite the fact that mutations occur constantly, there are a number of factors, the so-called mutagens, increasing the likelihood of mutations occurring.

Mutagens are factors that increase the likelihood of mutations.

Mutagens can be:

• chemicals (acids, alkalis, etc.);
• temperature effects;
• UV radiation;
• radiation;
• viruses.

Carcinogens- factors that increase the likelihood of occurrence malignant neoplasms(tumors) in animals and humans.

According to the nature of the genome change, mutations are distinguished:

• gene (point)
• chromosomal
• genomic

GENE MUTATIONS

Genetic, or point mutations --the result of a change in the nucleotide sequence in a DNA molecule within one gene.

If such a mutation occurs in a gene, it results in a change in the mRNA sequence. And a change in the sequence of mRNA can lead to a change in the sequence of amino acids in the polypeptide chain. As a result, another protein is synthesized, and some characteristic changes in the body.

This is the most common type of mutation and the most important source of hereditary variability in organisms.

Exist different types gene mutations associated with the addition, deletion or rearrangement of nucleotides in a gene:

• duplications- repetition of a gene section,
• inserts- the appearance of an extra pair of nucleotides in the sequence,
• deletions--loss of one or more nucleotide pairs,
• nucleotide pair substitutions- AT -><- ГЦ; AT -> <- ЦГ; или AT -> <- ТА,
• inversions- flipping a gene section by 180°.

The effects of gene mutations are extremely varied.

Most of them are neutral mutations.

CHROMOSOMAL MUTATIONS

Chromosomal mutations- These are changes in the structure of chromosomes. Typically, they can be identified and studied under a light microscope.
Different types of chromosomal rearrangements are known:

• deletion- loss of a chromosome section in its middle part;
• duplication- double or multiple repetition of genes localized in a certain region of the chromosome;
• inversion- rotation of a chromosome section by 180°, as a result of which genes in this section are located in the reverse sequence compared to the usual one;
• translocation- change in the position of any part of a chromosome in the chromosome set. The most common type of translocation is the exchange of sections between two non-homologous chromosomes. A section of a chromosome can change its position without exchange, remaining in the same chromosome or being included in some other one.

GENOMIC MUTATIONS

TO genomic mutationsrefers to a change in the number of chromosomes:

• aneuploidy;
• polyploidy.

Aneuploidy- increase or decrease in the number of chromosomes in the genotype.

It occurs when chromosomes do not separate in meiosis or chromatids in mitosis.

Aneuploids are found in plants and animals and are characterized by low viability.

Due to the nondisjunction of any pair of homologous chromosomes in meiosis, one of the resulting gametes contains one chromosome less, and the other contains one chromosome more, than in the normal haploid set. When merging with another gamete, a zygote appears with a smaller or larger number of chromosomes compared to the diploid set characteristic of the species. An example is trisomy 21 (extra 21st chromosome), leading to Down syndrome (Fig. 3).

Rice. 3. Down syndrome

Polyploidy- this is a multiple increase in the haploid set of chromosomes (Зn, 4n, etc.).

Most often it appears when there is a violation of the divergence of chromosomes to the poles of the cell in meiosis or mitosis under the influence of mutagenic factors.

It is widespread in plants and protozoa and extremely rare in animals.

With an increase in the number of chromosome sets in the karyotype, the reliability of the genetic system increases and the likelihood of decreased viability in the event of mutations decreases. Therefore, polyploidy often entails an increase in viability, fertility and other life properties (Fig. 4).

Rice. 4. Common and polyploid evening primrose plant

In plant growing, this property is used to artificially obtain polyploid varieties of cultivated plants that are characterized by high productivity.

In higher animals, polyploidy, as a rule, does not occur (exceptions are known among amphibians and rock lizards).

Hereditary diseases

In a diploid organism, most new mutations do not manifest themselves phenotypically because they are recessive. This is very important for the existence of the species, since most newly occurring mutations are harmful. However, their recessive nature allows them to persist for a long time in individuals of the species in a heterozygous state without harm to the body and appear in the future upon transition to a homozygous state.

Hereditary diseases:

• interlocked with the floor(genes on sex chromosomes - color blindness, hemophilia);
  
  Klinefelter syndrome is a pathology characterized by the presence of an extra X chromosome (at least one) in boys, as a result of which their puberty is disrupted. The disease was first described by Klinefelter in 1942. Some boys may have 3, 4 or 5 X chromosomes with one Y chromosome. As the number of X chromosomes increases, the severity of developmental defects and mental retardation also increases. For example, the variant of chromosome set 43 XXXXXV has so many characteristic features that it can be diagnosed in childhood (Fig. 5).
  

  

• Rice. 5. Klinefelter syndrome

  • autosomal dominant(in autosomes, Aa and AA): appear more often → are more subject to natural selection;
  • autosomal recessive(in autosomes, aa only): manifest less frequently → are less subject to natural selection → persist in populations longer; more often manifested in closely related crossings (isolated populations, ethnic and religious groups, ruling dynasties, etc.).

  Many autosomal recessive diseases are associated with metabolic disorders.

  For example, phenylketonuria- 1 in 1000 cases. There is no enzyme that converts the amino acid phenylalanine into tyrosine → accumulation of phenylalanine → damage to the nervous system → dementia (Fig. 6).

  

  Rice. 6. Patient with phenylketonuria

  Leucinosis- a severe hereditary disease, which is associated with a violation of amino acid metabolism, has an autosomal recessive type of inheritance. The disease is better known as maple syrup disease. The disease got its name because of the specific smell of urine, which is similar to the smell of maple syrup. With this pathology, the child’s body is unable to absorb amino acids: leucine, isoleucine, valine. Urine acquires a specific odor due to the presence of a substance formed from leucine.

  At the same time, there are a number of cases where a change in only one base in a certain gene has a noticeable effect on the phenotype (gene mutation).

  One example of a gene mutation is sickle cell anemia. The recessive allele, which causes this hereditary disease in the homozygous state, is expressed in the replacement of just one amino acid residue in the β-chain of the hemoglobin molecule (glutamic acid → valine). This leads to the fact that in the blood red blood cells with such hemoglobin are deformed (from round to sickle-shaped) and quickly destroyed (Fig. 7). In this case, acute anemia develops and a decrease in the amount of oxygen carried by the blood is observed. Anemia causes physical weakness, problems with the heart and kidneys, and can lead to early death in people homozygous for the mutant allele.

  

  Rice. 7. Normal red blood cell and red blood cell in sickle cell anemia
  

  Cytoplasmic variability

  Cytoplasmic mutations- associated with mutations of genes located in mitochondrial DNA and plastid DNA.

  During sexual reproduction cytoplasmic mutationsinherited through the mother's line, since during fertilization the zygote receives all the cytoplasm from the egg.

  In higher plants, variegated mutants in some cases are an example of the occurrence plastid mutations. For example: the variegation of night beauty (Fig. 8) and snapdragon (Fig. 9) is associated with mutations in chloroplasts.

  

  Rice. 8. Variegation of night beauty Fig. 9. Variegation of snapdragons

  Spontaneous cytoplasmic mutations are detected less frequently than mutations of chromosomal genes. This can be explained by a number of reasons. Obviously, one of the reasons lies in the multiplicity of cytoplasmic structures and organelles. Any cytoplasmic mutation that arises in one of many identical organelles cannot manifest itself until it multiplies in the cytoplasm of the cell.

  A cytoplasmic mutation can manifest itself in two cases: if a given organelle in a cell is single or represented by a small and constant number, or if the mutagen has a specific effect on the cell organelles, causing a massive change in them.

  Chlamydomonas turned out to be a very convenient object for studying cytoplasmic mutations. Streptomycin causes a large number of mutations of non-chromosomal genes in her. When strains sensitive to this antibiotic were treated with streptomycin solution, mutants resistant to streptomycin were isolated.

What are mutations? How do they arise?

Mutations are stable changes in the structure of hereditary material at any level of its organization. The result of mutations is changes in characteristics.

The term was introduced into scientific circulation by the Dutch botanist Hugo De Vries, who is also the creator of the mutation theory - despite the passage of almost a century and a half since then, his research is still relevant.

Are mutations passed on through generations?

Mutations are inherited - in other words, they can be transmitted from previous generations to the next.

What is the direction of mutations?

Mutations are not directed. Any locus can mutate, and this leads to changes in both insignificant traits and those that are vital. Mutations are called qualitative changes. They are individual, that is, they appear in individual organisms. Identical mutations may appear more than once. Mutagenesis is the process of forming mutations. Environmental factors that promote mutagenesis are called mutagens.

How do mutations differ depending on the type of body cell in which they occurred?

Based on the cell type, it is customary to distinguish between generative and somatic mutations. The first type occurs in germ cells and is in no way capable of influencing the characteristics of a particular organism. They will appear only in representatives of the new generation. Mutations of the second type, somatic, occur in somatic cells and can manifest themselves in this organism.

Are somatic mutations passed on to offspring? Why?

This type of mutation cannot be passed on to offspring during sexual reproduction. This phenomenon is due to the fact that somatic cells themselves are very rarely transmitted to offspring.

What mutations can be transmitted in plants - somatic or generative? Why?

But in plants, somatic mutations can be transmitted to descendants - however, only through asexual vegetative propagation: with the help of leaves, roots, shoot cuttings, etc.

What three groups of mutations are distinguished according to their adaptive value?

The following groups are distinguished: beneficial, harmful (or lethal, or semi-lethal) and neutral mutations. Science believes that most mutations are harmful. However, useful ones increase the vitality of the body. It was they who ensured the acquisition of new and diverse characters during evolution. Lethal mutations lead to death, semi-lethal mutations reduce viability, while neutral mutations have no effect on overall viability.

Can the adaptive value of mutations change under the influence of environmental conditions?

The same mutations under different conditions can cause both harm and benefit. There is a well-known example of the heterozygous sickle cell mutation in Africans (Aa) - this malfunction in the body, leading to hemoglobin abnormalities, simultaneously protects the carrier from malaria.

What two types of mutations are distinguished based on the nature of their manifestation?

There are dominant and recessive mutations. In the case where a dominant mutation is dangerous, the organism may die at one of the first stages of ontogenesis. Recessive mutations cannot appear in heterozygotes, as a result of which they remain in the population for a long time in a latent state.

What is the significance of beneficial mutations for organisms?

Beneficial recessive mutations create a reserve of hereditary variability. If the environment changes, carriers of these mutations are able to gain superiority in the struggle for survival.

What types of mutations are distinguished depending on whether the mutagen that led to the mutation has been identified?

Based on whether detection of the mutagen has become possible or not, two types of mutations are distinguished: induced and spontaneous. As a rule, spontaneous mutations occur naturally, while induced mutations are artificially caused.

What types of mutations are distinguished according to the criterion of location in the cell?

Based on their location in the cell, nuclear and cytoplasmic mutations are distinguished. Examples of cytoplasmic mutations are variegation of violet, mirabilis or night beauty, snapdragon (genes in chloroplasts), synthesis of respiratory enzymes in the cell (genes in mitochondria).