Types of hereditary variability. Hereditary and non-hereditary variability

Variation in biology is the occurrence of individual differences between individuals of the same species. Due to variability, the population becomes heterogeneous, and the species has a better chance of adapting to changing environmental conditions.

In a science like biology, heredity and variation go hand in hand. There are two types of variability:

• Non-hereditary (modification, phenotypic).
• Hereditary (mutational, genotypic).

Non-hereditary variability

Modification variability in biology is the ability of a single living organism (phenotype) to adapt to environmental factors within its genotype. Due to this property, individuals adapt to changes in climate and other conditions of existence. underlies the adaptation processes occurring in any organism. So, in outbred animals, with the improvement of conditions of detention, productivity increases: milk yield, egg production, and so on. And the animals brought to the mountainous regions grow undersized and with a well-developed undercoat. Changes in environmental factors and cause variability. Examples of this process can be easily found in everyday life: human skin becomes dark under the influence of ultraviolet rays, muscles develop as a result of physical exertion, plants grown in shaded places and in the light have different leaf shapes, and hares change coat color in winter and summer.

Non-hereditary variability is characterized by the following properties:

• group character of changes;
• not inherited by offspring;
• change in trait within the genotype;
• the ratio of the degree of change with the intensity of the impact of an external factor.

hereditary variability

In biology, hereditary or genotypic variability is the process by which the genome of an organism changes. Thanks to her, the individual acquires features that were previously unusual for her species. According to Darwin, genotypic variation is the main engine of evolution. There are the following types of hereditary variability:

• mutational;
• combinative.

Occurs as a result of the exchange of genes during sexual reproduction. At the same time, the traits of the parents are combined in different ways in a number of generations, increasing the diversity of organisms in the population. Combinative variability obeys the rules of Mendelian inheritance.

An example of such variability is inbreeding and outbreeding (closely related and unrelated crossing). When the traits of an individual producer want to be fixed in the breed of animals, then inbreeding is used. Thus, the offspring becomes more uniform and reinforces the qualities of the founder of the line. Inbreeding leads to the manifestation of recessive genes and can lead to the degeneration of the line. To increase the viability of the offspring, outbreeding is used - unrelated crossing. At the same time, the heterozygosity of the offspring increases and the diversity within the population increases, and, as a result, the resistance of individuals to the adverse effects of environmental factors increases.

Mutations, in turn, are divided into:

• genomic;
• chromosomal;
• genetic;
• cytoplasmic.

Changes affecting sex cells are inherited. Mutations in can be transmitted to offspring if the individual reproduces vegetatively (plants, fungi). Mutations can be beneficial, neutral or harmful.

Genomic mutations

Variation in biology through genomic mutations can be of two types:

• Polyploidy - a mutation often found in plants. It is caused by a multiple increase in the total number of chromosomes in the nucleus, is formed in the process of violation of their divergence to the poles of the cell during division. Polyploid hybrids are widely used in agriculture- in crop production there are more than 500 polyploids (onion, buckwheat, sugar beet, radish, mint, grapes and others).
• Aneuploidy is an increase or decrease in the number of chromosomes in individual pairs. This type of mutation is characterized by low viability of the individual. A widespread mutation in humans - one in the 21st pair - causes Down's syndrome.

Chromosomal mutations

Variability in biology by way appears when the structure of the chromosomes themselves changes: loss of the terminal section, repetition of a set of genes, rotation of a single fragment, transfer of a chromosome segment to another place or to another chromosome. Such mutations often occur under the influence of radiation and chemical pollution of the environment.

Gene mutations

A significant part of these mutations does not appear externally, as it is a recessive trait. Gene mutations are caused by a change in the sequence of nucleotides - individual genes - and lead to the appearance of protein molecules with new properties.

Gene mutations in humans cause the manifestation of some hereditary diseases - sickle cell anemia, hemophilia.

Cytoplasmic mutations

Cytoplasmic mutations are associated with changes in the structures of the cell cytoplasm containing DNA molecules. These are mitochondria and plastids. Such mutations are transmitted through the maternal line, since the zygote receives all the cytoplasm from the maternal egg. An example of a cytoplasmic mutation that has caused variability in biology is plant pinnateness, which is caused by changes in chloroplasts.

All mutations have the following properties:

• They appear suddenly.
• Passed down by inheritance.
• They don't have any direction. Mutations can be subjected to both an insignificant area and a vital sign.
• Occur in individuals, that is, individual.
• In their manifestation, mutations can be recessive or dominant.
• The same mutation can be repeated.

Each mutation is caused by specific causes. In most cases, it cannot be accurately determined. Under experimental conditions, to obtain mutations, a directed factor of the external environment is used - radiation exposure and the like.

Think!

Questions

1. What chromosomes are called sex chromosomes?

2. What are autosomes?

3. What is homogametic and heterogametic sex?

4. When does genetic sex determination occur in humans and what causes it?

5. What mechanisms of sex determination do you know? Give examples.

6. Explain what sex-linked inheritance is.

7. How is color blindness inherited? What color perception will be in children whose mother is color blind, and whose father has normal vision?

Explain from the standpoint of genetics why there are many more color blind people among men than among women.

Variability- one of the most important properties of living things, the ability of living organisms to exist in various forms, to acquire new features and properties. There are two types of variability: non-hereditary(phenotypic, or modification) and hereditary(genotypic).

■ Non-hereditary (modification) variability. This type of variability is the process of the emergence of new traits under the influence of environmental factors that do not affect the genotype. Consequently, the resulting modifications of signs - modifications - are not inherited. Two identical (monozygous) twins, having exactly the same genotypes, but by the will of fate grown up in different conditions, can be very different from each other. A classic example proving the influence of the external environment on the development of traits is the arrowhead. This plant develops three types of leaves, depending on the growing conditions - in the air, in the water column or on the surface.

Under the influence of ambient temperature, the color of the coat of the Himalayan rabbit changes. The embryo, developing in the womb, is in conditions of elevated temperature, which destroys the enzyme necessary for dyeing wool, so rabbits are born completely white. Shortly after birth, certain protruding parts of the body (nose, tips of the ears and tail) begin to darken, because there the temperature is lower than in other places, and the enzyme is not destroyed. If you pluck an area of ​​white wool and cool the skin, black wool will grow in this place.

Under similar environmental conditions in genetically close organisms, modification variability has a group character, for example, in summer, under the influence of UV rays, a protective pigment, melanin, is deposited in the skin of most people under the influence of UV rays, people sunbathe.

In the same species of organisms, under the influence of environmental conditions, the variability of various traits can be completely different. For example, in a large cattle milk yield, weight, fertility very much depend on the conditions of feeding and keeping, and, for example, the fat content of milk under the influence external conditions very little changes. Manifestations of modification variability for each trait are limited by their reaction rate. reaction rate- these are the limits in which a change in a trait is possible in a given genotype. In contrast to the modification variability itself, the reaction rate is inherited, and its boundaries are different for different signs and in individual individuals. The narrowest reaction rate is typical for traits that provide the vital qualities of the body.

Due to the fact that most modifications have an adaptive value, they contribute to adaptation - the adaptation of the body within the limits of the norm of reaction to existence in changing conditions.

■ Hereditary (genotypic) variability. This type of variability is associated with changes in the genotype, and the traits acquired as a result of this are inherited by the next generations. There are two forms of genotypic variability: combinative and mutational.

Combination variability consists in the appearance of new traits as a result of the formation of other combinations of parental genes in the genotypes of offspring. This type of variability is based on independent divergence of homologous chromosomes in the first meiotic division, random meeting of gametes in the same parental pair during fertilization, and random selection of parental pairs. It also leads to recombination of the genetic material and increases the variability of the exchange of sections of homologous chromosomes, which occurs in the first prophase of meiosis. Thus, in the process of combinative variability, the structure of genes and chromosomes does not change, however, new combinations of alleles lead to the formation of new genotypes and, as a result, to the appearance of offspring with new phenotypes.

Mutational variability It is expressed in the appearance of new qualities of the organism as a result of the formation of mutations. The term "mutation" was first introduced in 1901 by the Dutch botanist Hugo de Vries. According to modern concepts, mutations are sudden natural or artificially induced inherited changes in the genetic material, leading to a change in certain phenotypic characteristics and properties of the organism. Mutations are undirected, that is, random, in nature and are the most important source of hereditary changes, without which the evolution of organisms is impossible. At the end of the XVIII century. in America, a sheep with shortened limbs was born, which gave rise to a new Ancon breed. in Sweden at the beginning of the 20th century. a mink with platinum fur was born on a fur farm. The huge variety of traits in dogs and cats is the result of mutational variation. Mutations arise abruptly, as new qualitative changes: awnless wheat was formed from spinous wheat, short wings and striped eyes appeared in Drosophila, white, brown, black color appeared in rabbits from the natural color of agouti as a result of mutations.

According to the place of origin, somatic and generative mutations are distinguished. Somatic mutations arise in the cells of the body and are not transmitted through sexual reproduction to the next generations. Examples of such mutations are age spots and skin warts. generative mutations appear in germ cells and are inherited.

According to the level of change in the genetic material, gene, chromosomal and genomic mutations are distinguished. Gene mutations cause changes in individual genes, disrupting the order of nucleotides in the DNA chain, which leads to the synthesis of an altered protein.

Chromosomal mutations affect a significant portion of the chromosome, leading to disruption of the functioning of many genes at once. A separate fragment of the chromosome can double or be lost, which causes serious disturbances in the functioning of the body, up to the death of the embryo in the early stages of development.

Genomic mutations lead to a change in the number of chromosomes as a result of violations of the divergence of chromosomes in the divisions of meiosis. The absence of a chromosome or the presence of an extra one leads to adverse consequences. The best-known example of a genomic mutation is Down syndrome, a developmental disorder that occurs when an extra chromosome 21 is added. In such people, the total number of chromosomes is 47.

In protozoa and in plants, an increase in the number of chromosomes, a multiple of the haploid set, is often observed. This change in the chromosome set is called polyploidy. The emergence of polyploids is associated, in particular, with the nondisjunction of homologous chromosomes during meiosis, as a result of which not haploid, but diploid gametes can form in diploid organisms.

Mutagenic factors. The ability to mutate is one of the properties of genes, so mutations can occur in all organisms. Some mutations are incompatible with life, and the embryo that received them dies in the womb, while others cause persistent changes in traits that are significant to varying degrees for the life of the individual. Under normal conditions, the mutation rate of an individual gene is extremely low (10 -5), but there are environmental factors that significantly increase this value, causing irreversible damage to the structure of genes and chromosomes. Factors whose impact on living organisms leads to an increase in the number of mutations are called mutagenic factors or mutagens.

All mutagenic factors can be divided into three groups.

Physical mutagens are all types of ionizing radiation (y-rays, x-rays), ultraviolet radiation, high and low temperatures.

Chemical mutagens- these are analogs of nucleic acids, peroxides, salts of heavy metals (lead, mercury), nitrous acid and some other substances. Many of these compounds cause disturbances in DNA replication. Substances used in agriculture to control pests and weeds (pesticides and herbicides), waste products from industrial enterprises, certain food dyes and preservatives, some drugs, tobacco smoke components have a mutagenic effect.

Special laboratories and institutes have been set up in Russia and other countries of the world to test all newly synthesized chemical compounds for mutagenicity.

4. THE ROLE OF HEREDITARY VARIABILITY IN THE EVOLUTION OF SPECIES AND ITS FORMS

In Darwin's evolutionary theory, the prerequisite for evolution is hereditary variability, and the driving forces of evolution are the struggle for existence and natural selection. When creating the evolutionary theory, Ch. Darwin repeatedly refers to the results of breeding practice. He showed that the diversity of varieties and breeds is based on variability. Variability is the process of the emergence of differences in descendants compared to ancestors, which determine the diversity of individuals within a variety or breed. Darwin believes that the causes of variability are the impact on organisms of environmental factors (direct and indirect), as well as the nature of the organisms themselves (since each of them reacts specifically to the impact of the external environment). Variability serves as the basis for the formation of new features in the structure and functions of organisms, and heredity reinforces these features. Darwin, analyzing the forms of variability, singled out three among them: definite, indefinite and correlative.

A certain, or group, variability is a variability that occurs under the influence of some environmental factor that acts equally on all individuals of a variety or breed and changes in a certain direction. Examples of such variability are an increase in body weight in animal individuals with good feeding, a change in the hairline under the influence of climate, etc. A certain variability is massive, covers the entire generation and is expressed in each individual in a similar way. It is not hereditary, that is, in the descendants of the modified group, under other conditions, the traits acquired by the parents are not inherited.

Indefinite, or individual, variability manifests itself specifically in each individual, i.e. unique, individual in nature. It is associated with differences in individuals of the same variety or breed under similar conditions. This form of variability is indefinite, i.e., a trait under the same conditions can change in different directions. For example, in one variety of plants, specimens appear with different colors of flowers, different intensity of color of petals, etc. The reason for this phenomenon was unknown to Darwin. Indefinite variability is hereditary, that is, it is stably transmitted to offspring. This is its importance for evolution.

With correlative, or correlative, variability, a change in any one organ causes changes in other organs. For example, dogs with poorly developed coats usually have underdeveloped teeth, pigeons with feathered legs have webbing between their toes, pigeons with a long beak usually have long legs, white cats with blue eyes usually deaf, etc. From the factors of correlative variability, Darwin draws an important conclusion: a person, selecting any feature of the structure, will almost "probably unintentionally change other parts of the body on the basis of the mysterious laws of correlation."

Having determined the forms of variability, Darwin came to the conclusion that only heritable changes are important for the evolutionary process, since only they can accumulate from generation to generation. According to Darwin, the main factors in the evolution of cultural forms are hereditary variability and human selection (Darwin called such selection artificial). Variability is a necessary prerequisite for artificial selection, but it does not determine the formation of new breeds and varieties.

CONCLUSION

Thus, Darwin for the first time in the history of biology built the theory of evolution. This was of great methodological significance and made it possible not only to substantiate the idea of ​​organic evolution clearly and convincingly for contemporaries, but also to test the validity of the theory of evolution itself. This was the decisive phase of one of the greatest conceptual revolutions in natural science. The most important thing in this revolution was the replacement of the theological idea of ​​evolution as a concept of primordial expediency by the model of natural selection. Despite fierce criticism, Darwin's theory quickly won recognition due to the fact that the concept of the historical development of wildlife is better than the idea of ​​the immutability of species, explained the observed facts. To substantiate his theory, Darwin, unlike his predecessors, drew on a huge amount of facts available to him from various fields. The prominence of biotic relations and their population-evolutionary interpretation was the most important innovation of Darwin's concept of evolution and gives the right to conclude that Darwin created his own concept of the struggle for existence, fundamentally different from the ideas of his predecessors. Darwin's doctrine of the evolution of the organic world was the first theory of development created by "naturally historical materialism in the depths of natural science, the first application of the principle of development to an independent field of natural sciences." This is the general scientific significance of Darwinism.

The merit of Darwin and that he opened driving forces organic evolution. The further development of biology deepened and supplemented his ideas, which served as the basis of modern Darwinism. In all biological disciplines, the leading place is now occupied by the historical method of research, which makes it possible to study the specific paths of evolution of organisms and penetrate deeply into the essence of biological phenomena. The evolutionary theory of Ch. Darwin has found wide application in the modern synthetic theory, where the only guiding factor of evolution is natural selection, the material for which is mutation. The historical analysis of Darwin's theory inevitably gives rise to new methodological problems of science, which can become the subject of a special study. The solution of these problems entails an expansion of the field of knowledge, and, consequently, scientific progress in many areas: both in biology, medicine, and in psychology, on which the evolutionary theory of Charles Darwin had no less influence than on the natural sciences.

List of used literature

1. Alekseev V.A. Fundamentals of Darwinism (historical and theoretical introduction). - M., 1964.

2. Velisov E.A. Charles Darwin. Life, activity and works of the founder of the evolutionary doctrine. - M., 1959.

3. Danilova V.S., Kozhevnikov N.N. Basic concepts of natural science. – M.: Aspect Press, 2000. – 256 p.

4. Dvoryansky F.A. Darwinism. - M.: MGU, 1964. - 234 p.

5. Lemeza N.A., Kamlyuk L.V., Lisov N.D. Handbook for applicants to universities. – M.: Rolf, Iris-press, 1998. – 496 p.

6. Mamontov S.G. Biology: a guide for applicants to universities. –M.: graduate School, 1992. - 245 p.

7. Ruzavin G.I. Concepts of modern natural science: a course of lectures. - M.: Project, 2002. - 336 p.

8. Sadokhin A.P. Concepts of modern natural science. - M., 2005.

9. Slopov E.F. Concepts of modern natural science. – M.: Vlados, 1999. – 232 p.

10. Smygina S.I. Concepts of modern natural science. - Rostov n / D., 1997.

Some particles passed from parents to offspring. Now we call these particles genes. The idea of ​​corpuscular heredity is of great importance for understanding how natural selection operates in populations. Evolution can be thought of as changes in any property of a given population over time. In a certain general philosophical sense, this is the essence of evolution. ...

They would strive to be preserved in changing conditions, and natural selection would have full scope for its improving action. 1. NATURAL SELECTION AS AN ELEMENTARY EVOLUTIONARY FACTOR I called the preservation of favorable individual differences and changes and the destruction of harmful ones natural selection or the survival of the fittest Ch. Darwin In the modern sense ...

Preservation and accumulation of small hereditary changes, each of which is beneficial to the creature being saved. Circumstances favoring the formation of new forms by natural selection. Much variability, of course, and individual differences will obviously be a favorable circumstance. A large number of individuals, increasing the chances of appearing in...

And so they play a more important role in evolution. Of fundamental importance is the fact that these mutations are random, in other words, they are not directed. 3. The central dogma and the Weismann principle are accepted. 4. Evolution is carried out by changing the frequencies of genes. 5. These changes can occur as a result of mutations, the entry of genes into the population and their outflow from it, random drift and ...

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

Heredity- the ability of organisms to transmit their characteristics and features of development to offspring.
Variability- a variety of characters among representatives of this species, as well as the property of offspring to acquire differences from parental forms.
Genetics- the science of the laws of heredity and variability.

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

History of the development of genetics

3. What methods of genetics as a science do you know?
The main method of genetics is hybridological. This is the crossing of certain organisms and the analysis of their offspring. This method was used by G. Mendel.
Genealogical - the study of pedigrees. Allows you to determine the patterns of inheritance of traits.
Twin - comparison of identical twins, allows you to study modification variability (determine the impact of the genotype and environment on the development of the child).
Cytogenetic - the study under a microscope of the chromosome set - the number of chromosomes, the features of their structure. Allows detection of chromosomal diseases.

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

5. Why can peas be considered a successful object of genetic research?
Pea species differ from each other in a small number of well-distinguishable characters. Peas are easy to grow, in the Czech Republic it breeds several times a year. In addition, in nature, peas are self-pollinators, but in the experiment, self-pollination is easily prevented, and the researcher can easily pollinate a plant with one pollen from another plant.

6. Inheritance of what pairs of traits in peas was studied by G. Mendel?
Mendel used 22 pure pea lines. The plants of these lines had strongly pronounced differences from each other: the shape of the seeds (round - wrinkled); color of seeds (yellow - green); bean shape (smooth - wrinkled); arrangement of flowers on the stem (axillary - apical); plant height (normal - dwarf).

7. What is meant in genetics by a clean line?
A pure line in genetics is a group of organisms that have some characteristics that are completely transmitted to offspring due to the genetic homogeneity of all individuals.

Patterns of inheritance. monohybrid cross

1. Give definitions of concepts.
allelic genes- genes responsible for the manifestation of one trait.
Homozygous organism An organism that contains two identical allelic genes.
heterozygous organism An organism that contains two different allelic genes.

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

3. Formulate the uniformity rule for hybrids of the first generation.
When crossing two homozygous organisms that differ from each other in one trait, all hybrids of the first generation will have the trait of one of the parents, and the generation for this trait will be uniform.

4. Formulate a splitting rule.
When two descendants (hybrids) of the first generation are crossed with each other in the second generation, splitting is observed and individuals with recessive traits appear again; these individuals make up ¼ of the total number of descendants of the first generation.

5. Formulate the law of purity of gametes.
When formed, only one of the two “elements of heredity” responsible for this trait falls into each of them.

6. Using generally accepted conventions, draw up a monohybrid crossing scheme.

Describe the cytological foundations of monohybrid crossing using this example.
P is the parental generation, F1 is the first generation of offspring, F2 is the second generation of offspring, A is the gene responsible for the dominant trait, and the gene responsible for the recessive trait.
As a result of meiosis, in the gametes of the parental individuals, there will be one gene responsible for the inheritance of a certain trait (A or a). In the first generation, somatic cells will be heterozygous (Aa), so half of the gametes of the first generation will contain the A gene, and the other half will contain the a gene. As a result of random combinations of gametes in the second generation, the following combinations will arise: AA, Aa, aA, aa. Individuals with the first three combinations of genes will have the same phenotype (due to the presence of a dominant gene), and with the fourth - a different (recessive).

7. Solve the genetic problem for monohybrid crossing.
Task 1.
In watermelon, the green color of the fruit dominates over the striped. From the crossing of a green-fruited variety with a striped-fruited one, hybrids of the first generation were obtained, having fruits of a green color. The hybrids were pollinated and received 172 hybrids of the second generation. 1) How many types of gametes does a green-fruited plant form? 2) How many F2 plants will be heterozygous? 3) How many different genotypes will there be in F2? 4) How many plants with striped fruit will be in F2? 5) How many homozygous plants with green fruits will be in F2?
Solution
A - green color, a - striped color.
Since when plants with green and striped fruits were crossed, plants with a green fruit were obtained, it can be concluded that the parental individuals were homozygous (AA and aa) (according to Mendel's rule of uniformity of hybrids of the first generation of Mendel).
Let's make a crossover scheme.

Answers:
1. 1 or 2 (in case of heterozygote)
2. 86
3. 3
4. 43
5. 43.

Task 2.
Long hair in cats is recessive to short hair. A longhair cat crossed with a heterozygous shorthair cat produced 8 kittens. 1) How many types of gametes does a cat have? 2) How many types of gametes are formed in a cat? 3) How many phenotypically different kittens are in the litter? 4) How many genotypically different kittens are in the litter? 5) How many kittens are in the litter with long hair?
Solution
A is short hair and a is long hair. Since the cat had long hair, it is homozygous, its genotype is aa. The cat has the Aa genotype (heterozygous, short hair).
Let's make a crossover scheme.

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

multiple alleles. Analyzing cross

1. Give definitions of concepts.
Phenotype- the totality of all signs and properties of the organism, which are revealed in the process of individual development under 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?
A gene for a trait may have other "conditions" that are neither dominant nor recessive. This phenomenon can occur as a result of mutations and is called "multiple allelism".

3. What is meant by multiple allelism?

Multiple allelism is the existence of more than two alleles of a given gene in a population.

4. Fill in the table.

Types of interaction of allelic genes

5. What is analyzing cross and what is its practical significance?
Analyzing crosses are used to establish the genotype of individuals that do not differ in phenotype. In this case, the individual whose genotype needs to be established is crossed with an individual homozygous for the recessive gene (aa).

6. Solve the problem of analyzing crossover.
A task.

The white color of the corolla in phlox dominates over pink. A plant with a white corolla is crossed with a plant with a pink color. 96 hybrid plants were obtained, of which 51 are white and 45 are pink. 1) What are the genotypes of the parent plants? 2) How many types of gametes can a plant with a white corolla color form? 3) How many types of gametes can a plant with a pink corolla color form? 4) What phenotype ratio can be expected in the F2 generation from crossing F1 hybrid plants with white flowers?
Solution.
A - white color, a - pink color. The genotype of one plant A .. is white, the second aa is pink.
Since splitting 1:1 (51:45) is observed in the first generation, the genotype of the first plant is Aa.
Let's make a crossover scheme.

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

Dihybrid cross

1. Give definitions of concepts.
Dihybrid cross- crossing individuals, which take into account differences from each other in two ways.
Punnett lattice is a table proposed by the English geneticist Reginald Punnett as a tool that 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 form of seeds.
Yellow smooth (AABB) × Green wrinkled (AABB) =
P: AaBv×AaBb (diheterozygotes)
Gametes: AB, Av, aB, av.
F1 in the table:

Answer: 9 (yellow smooth): 3 (green smooth): 3 (yellow wrinkled): 1 (green wrinkled).

3. Formulate the law of independent inheritance of traits.
In a dihybrid cross, the genes and traits for which these genes are responsible are inherited independently of each other.

4. Solve genetic problems for dihybrid crossing.
Task 1.

Black color in cats dominates over fawn, and short hair dominates over long. Crossed purebred Persian cats (black longhair) with Siamese (fawn shorthair). The resulting hybrids were crossed with each other. What is the probability of getting a purebred Siamese kitten in F2; a kitten phenotypically similar to a Persian; long-haired fawn kitten (express in parts)?
Solution:
A - black color, and - fawn.
B - short hair, c - long.

Let's create a Punnett lattice.

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

Task 2.

In tomatoes, the round shape of the fruit dominates over the pear-shaped, and the red color of the fruit dominates over the yellow. 120 plants were obtained from crossing a heterozygous plant with a red color and a pear-shaped fruit and a yellow-fruited plant with rounded fruits. 1) How many types of gametes does a heterozygous plant with a red color of fruits and a pear-shaped form form? 2) How many different phenotypes are obtained from such crossing? 3) How many different genotypes were obtained from such a crossing? 4) How many plants turned out with a red color and a rounded shape of the fruit? 5) How many plants turned out with a yellow color and a rounded shape of the fruit?
Solution
A - rounded shape, a - pear-shaped.
B - red color, c - yellow color.
We determine the genotypes of the parents, the types of gametes and write down the crossing scheme.

Let's create a Punnett lattice.

Answer:
1. 2
2. 4
3. 4
4. 30
5. 30.

Chromosomal theory of heredity. Modern ideas about the gene and genome

1. Give definitions of concepts.
Crossing over- the process of exchanging sections of homologous chromosomes during conjugation in prophase I of meiosis.
Chromosomal map- this is a diagram of the mutual arrangement and relative distances between the genes of certain chromosomes that are in the same linkage group.

2. In what case does the violation of the law of independent inheritance of traits occur?
When crossing over, Morgan's law is violated, and the genes of one chromosome are not inherited linked, since some of them are replaced by allelic genes of the homologous chromosome.

3. Write the main provisions of T. Morgan's chromosome 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 arranged linearly on chromosomes, that is, one after another.
In the process of gamete formation, 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 fall into the same gamete, that is, they are inherited linked.

5. What determines the probability of divergence of two non-allelic genes during crossing over?
The probability of divergence of two non-allelic genes during crossing over depends on the distance between them in the chromosome.

6. What underlies the compilation of genetic maps of organisms?
Calculating the frequency of crossing over between any two genes of the same chromosome responsible for different traits makes it possible to accurately determine the distance between these genes, and hence start building a genetic map, which is a diagram of the mutual arrangement of genes that make up one chromosome.

7. What are chromosome maps for?
With the help of genetic maps, you can find out the location of animal and plant genes and information from them. This will help in the fight against various incurable diseases.

Hereditary and non-hereditary variability

1. Give definitions of concepts.

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

3. What determines the limits of modification variability?
The limits of modification variability depend on the rate of reaction, which is genetically determined and inherited.

4. What do combinative and mutational variability have in common and how do they differ?
General: both types of variability are due to changes in the genetic material.
Differences: combinative variability occurs due to the recombination of genes during the fusion of gametes, and mutational variability is caused by the action of mutagens on the body.

5. Fill in the table.

Types of mutations

6. What is meant by mutagenic factors? Give relevant examples.
Mutagenic factors - influences leading to the occurrence of mutations.
These can be physical effects: ionizing radiation and ultraviolet radiation that damages 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.
Genetic diseases- diseases caused by gene or chromosomal mutations.
Chromosomal diseases- diseases caused by a change in the number of chromosomes or their structure.

2. Fill in the table.

Inheritance of traits in humans

3. What is meant by sex-linked inheritance?
Sex-linked inheritance is the inheritance of traits whose genes are located on the sex chromosomes.

4. What traits are sex-linked in humans?
Sex-linked hemophilia and color blindness are inherited in humans.

5. Solve genetic problems for the inheritance of traits in humans, including sex-linked inheritance.
Task 1.

In humans, the gene for long eyelashes is dominant over the gene for short eyelashes. A woman with long eyelashes, whose father had short eyelashes, married men with short eyelashes. 1) How many types of gametes are formed in a woman? 2) How many types of gametes are formed in men? 3) What is the probability of the birth of a child with long eyelashes in this family (in %)? 4) How many different genotypes and how many phenotypes can be among the children of this married couple?
Solution
A - long eyelashes
a - short eyelashes.
The female is heterozygous (Aa) because her father had short eyelashes.
The male is homozygous (aa).

Answer:
1. 2
2. 1
3. 50
4. 2 genotypes (Aa) and 2 phenotypes (long and short eyelashes).

Task 2.

In humans, a free earlobe dominates over a closed one, and a smooth chin is recessive to a chin with a triangular fossa. These traits are inherited independently. From the marriage of a man with a closed earlobe and a triangular fossa on his chin and a woman with a free earlobe and a smooth chin, a son was born with a smooth chin and a closed earlobe. What is the probability of the birth in this family of a child with a smooth chin and free earlobe; with a triangular fossa on the chin (in %)?
Solution
A - free earlobe
a - not free earlobe
B - triangular fossa
c - smooth chin.
Since the couple had a child with homozygous traits (aavb), the genotype of the mother is Aavb, and the father is aaBv.
Let's write down the genotypes of the parents, the types of gametes and the crossing scheme.

Let's create a Punnett lattice.

Answer:
1. 25
2. 50.

Task 3.

In humans, the gene that causes hemophilia is recessive and is located on the X chromosome, while albinism is caused by an autosomal recessive gene. Parents, normal in these characteristics, had a son with an albino and a hemophiliac. 1) What is the probability that their next son will show these two abnormal features? 2) What is the probability of having healthy daughters?
Solution:
X° - the presence of hemophilia (recessive), X - the absence of hemophilia.
A - normal skin color
a is an albino.
Parents' genotypes:
Mother - Х°ХАа
Father - HUAA.
Let's create a Punnett lattice.

Answer: the probability of manifestation of signs of albinism and hemophilia (genotype X ° Uaa) - in the next son - 6.25%. The probability of the birth of healthy daughters - (XXAA genotype) - 6.25%.

Task 4.

Hypertension in humans is determined by a dominant autosomal gene, while optic atrophy is caused by a sex-linked recessive gene. A woman with optic atrophy married a man with hypertension whose father also had hypertension and whose mother was healthy. 1) What is the probability that a child in this family will suffer from both anomalies (in %)? 2) What is the probability of having a healthy baby (in %)?
Solution.
X° - the presence of atrophy (recessive), X - the absence of atrophy.
A - hypertension
a - no hypertension.
Parents' genotypes:
Mother - X ° X ° aa (as she is ill with atrophy and without hypertension)
Father - XUAa (since he is not sick with atrophy and his father was with hypertension, and his mother is healthy).
Let's create a Punnett lattice.

Answer:
1. 25
2. 0 (only 25% of daughters will not have these deficiencies, but they will be carriers of atrophy and without hypertension).

Heredity - this is the property of living organisms to preserve and transmit signs in a number of generations. Due to heredity from generation to generation, the characteristics of the species, breed are preserved.

Hereditary variability (mutational or genotypic) associated with a change in the genotype of an individual, so the resulting changes are inherited. It is the material for natural selection. Darwin called this heredity indeterminate. Mutations are the basis of hereditary variability - sudden abrupt and non-directional changes in the original form. They lead to the appearance in living organisms of qualitatively new hereditary traits and properties that did not previously exist in nature. The source of hereditary variability is the mutational process. There are several types of mutations: genomic, chromosomal and gene.

Genomic mutations (polyploidy and aneuploidy) are changes in the number of chromosomes. Polyploidy is a multiple increase in the haploid set of chromosomes (Zn, 4n, etc.). Most often, polyploidy is formed when the divergence of chromosomes to the poles of the cell is disturbed during meiosis or mitosis under the influence of mutagenic factors. It is widely distributed in plants and extremely rare in animals.

Aneuploidy - increase or decrease in the number of chromosomes for individual pairs. 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.

Chromosomal mutations are changes in the structure of chromosomes. There are the following types of chromosomal mutations:

Deficiency - Loss of end segments of chromosomes.

Deletions - Loss of a portion of a chromosome arm.

duplication - repetition of a set of genes in a certain region of the chromosome.

Inversion - rotation of a segment of chromosomes by 180°.

Translocation - transfer of a site to the other end of the same chromosome or to another, non-homologous chromosome.

Gene mutations - changes in the nucleotide sequence of a DNA molecule (gene). Their result is a change in the sequence of amino acids in the polypeptide chain, and the appearance of a protein with new properties. Most gene mutations do not appear phenotypically because they are recessive.

Cytoplasmic mutations - associated with changes in cytoplasmic organelles containing DNA (mitochondria and plastids). These mutations are inherited through the maternal line, as the zygote receives the entire cytoplasm from the ovum during opsn-addition. Example: Plant variegation is associated with mutations in chlorolllasts.

Significance in evolution and ontogenesis Mutations that affect germ cells (generative mutations) appear in the next generation. Mutations in somatic cells are manifested in those organs that include altered cells. In animals, somatic mutations are not inherited, since a new organism does not arise from somatic cells. In vegetatively propagated plants, somatic mutations may persist. Mutational variability plays the role of the main supplier of hereditary changes in evolution. It is she who is the primary material of all evolutionary transformations.

Genotypic variability and its types. Significance in ontogeny and evolution.

Genotypic, or hereditary variability, represents changes in the phenotype due to changes in the genotype.

It is caused by mutations and their combinations during sexual reproduction (for example, inherited polledness in cattle).

Depending on the nature of the variation of the genetic material, combinative and mutational hereditary variability are distinguished. Combinative variability is due to the formation in the offspring of new combinations of genes in genotypes, which are formed as a result of the recombination of genes and chromosomes in the process of sexual reproduction. The infinite variety of genotypes of living organisms, the uniqueness of each genotype are due to combinative variability. With this type of variability, the combinations of genes and the nature of their interaction in the genotype change, while the genes themselves remain unchanged.

Combination variability , resulting from the recombination of parental genes in the genotypes of offspring, is based on three main mechanisms.

1. Independent divergence into daughter cells (spermatocytes II, oocyte II and the first reduction body) of homologous chromosomes from each pair (takes place during the first division of meiosis during gametogenesis). For example, even for 2 pairs of chromosomes, 2 variants of chromosome divergence into daughter cells and 4 types of spermatozoa are possible (Fig. 76).

2. Random combination of gametes, and therefore, homologous (paternal and maternal) chromosomes during fertilization. For the 4 types of sperm noted above, the participation of one of them in the fertilization of the egg will be purely random, and the results of a specific combination of one of the variants of male chromosomes with one (also from 4 possible ones) will be different, since three variants were carried away by reduction bodies and ceased to exist ) from variants of female chromosomes homologous to them.

3. Exchange of individual alleles between homologous chromosomes in the process of meiotic crossing over. After it, the combinations of alleles in the sperm chromosomes are characterized by new variants that differ from those of the body's somatic cells (Fig. 77).

Crossing over occurs at the beginning of meiosis, when homologous chromosomes line up opposite each other. In this case, sections of homologous chromosomes cross, break off, and then reattach, but to another chromosome. Ultimately, four chromosomes are formed with different combinations of genes. Chromosomes, called "recombinant", carry new combinations of genes (Ab and aB) that were absent in the original chromosomes (AB and ab)

Combinative variability explains why new combinations of signs of relatives on the maternal and paternal lines are found in children, and in such specific variants that were not characteristic of either the father, or the mother, or grandfather, or grandmother, etc.

Thanks to combinative variability, a variety of genotypes is created in the offspring, which is of great importance for the evolutionary process due to the fact that: 1) the diversity of material for the evolutionary process increases without reducing the viability of individuals; 2) the possibilities of adaptation of organisms to changing environmental conditions are expanded and thereby the survival of a group of organisms (population, species) as a whole is ensured.

Combinative variability is used in breeding in order to obtain a more economically valuable combination of hereditary traits. In particular, the phenomenon of heterosis, increased viability, growth intensity and other indicators is used during hybridization between representatives of different subspecies or varieties. The opposite effect is produced by the phenomenoninbreeding or inbreeding - crossing organisms that have common ancestors. The common origin of crossed organisms increases their probability of having the same alleles of any genes, and, consequently, the probability of the appearance of homozygous organisms. The highest degree of inbreeding is achieved during self-pollination in plants and self-fertilization in animals. Homozygosity increases the possibility of manifestation of recessive allelic genes, mutagenic changes in which lead to the appearance of organisms with hereditary anomalies.

The results of studying the phenomenon of combinative variability are used in medical genetic counseling, especially at its second and third stages: prognosis of offspring, formation of a conclusion and explanation of the meaning of genetic risk.

Along with marriage systems, there are two types of formation of marriage couples:

1) positive assortative (selective) formation of marriage pairs, or more frequent marriage of individuals similar in certain phenotypic characteristics (marriages between deaf-mutes, or similar in height, mental development, etc.);

2) negative assortative mating, or the rarer marriage of individuals with similar certain traits (for example, red-haired individuals avoid marrying each other).

Both inbreeding and positive assortative mating increase (the latter, though to a lesser extent) the level of homozygosity of the offspring, including the loci of deleterious recessive alleles. Outbreeding, on the contrary, increases the degree of heterozygosity and in many cases increases the level of viability. The possible consequences of inbreeding and positive assortative formation of marriage pairs are used in medical genetic counseling of potential marriage partners.

Mutations - these are inherited changes in the genetic material, leading to a change in the characteristics of the organism. The foundations of the doctrine of mutations were laid by G. de Vries already in 1901, who described mutations in elotera, but their molecular mechanisms were studied much later. According to G. de Vries, a mutation is an abrupt, intermittent change in a hereditary trait.

The essence of the mutational theory of G. de Vries is reduced to the following provisions:

1) mutation occurs discretely, without transitions;

2) new forms are constant;

3) mutations are multidirectional (beneficial and harmful);

4) the detection of mutations depends on the sample size of the studied organisms;

5) the same mutations can occur repeatedly.

Mutational changes are extremely diverse. They can affect almost all morphological, physiological and biochemical characteristics of the body, can cause sharp or, conversely, barely noticeable phenotypic deviations from the norm.

Mutational variability is based on structural changes in genes and chromosomes. Depending on the nature of the changes in the genetic material, there are:

1) gene (point) mutations, which are insertion, loss, replacement or change in a pair of nucleotides;

2) insertions - insertions (“insertions”) of DNA molecules or their fragments into a gene, most often leading to its inactivation or to a strong polar effect in operons;

3) chromosomal rearrangements, or aberrations - transformations of the structure of chromosomes based on their break;

4) genomic (genotypic) mutations, consisting in a change in the number of chromosomes in a cell.

Phenotypic variability and its types. Adaptive nature of modifications. The reaction rate of the sign. Expressivity and penetrance of the trait.

Modification (phenotypic) variability due to the influence of only external conditions and is not associated with a change in the genotype. Specific variants of the state of the phenotype with modification variability are called modifications. Of greatest interest areadaptive modifications - non-inherited changes that are beneficial to the body, contributing to its survival in changed conditions. Unlike mutations (rare, single and random events), adaptive modifications are directed and at the same time often reversible, predictable and often characteristic of large groups of organisms. The basis for the existence of modifications is that the phenotype is the result of the interaction of the genotype and external conditions. Therefore, a change in external conditions can cause changes in the phenotype, not accompanied by changes in the genotype. The mechanism of the occurrence of modifications is that environmental conditions affect the enzymatic reactions (metabolic processes) occurring in the developing organism, and to a certain extent change their course, and, consequently, the result - the state of the trait formed on their basis.

Modifications have the following properties:

1) the degree of severity of the modification is proportional to the strength and duration of the effect on the body of the factor causing the modification (this pattern fundamentally distinguishes modifications from mutations, especially gene ones);

2) in the vast majority of cases, modification is a useful adaptive reaction of the body in response to the action of one or another external factor

3) only those modifications are adaptive , which are caused by ordinary changes in natural conditions, which the ancestors of individuals of a given species repeatedly "faced" during its past evolutionary history;

4) modifications caused by experimental influences, especially chemical and physical factors that the organism does not encounter in nature, as a rule, do not have an adaptive value, and often represent malformations and deformities. The modifications induced in this way are often referred to as morphoses.

5) in contrast to mutations, which are characterized by high constancy, modifications have varying degrees of stability. Many of them are reversible, i.e. the changes that have arisen gradually disappear if the action of the factor that caused them ceases. So, a person’s tan disappears when the skin ceases to be exposed to insolation, muscle volume decreases after the end of training, etc.

6) modifications, unlike mutations, are not inherited, i.e. are non-hereditary. This is consistent with the “central dogma of molecular biology” by F. Crick, according to which the transfer of information is possible only from genetic material to gene products-proteins, but not in the opposite direction.

External conditions have a huge impact on all the signs and properties of a developing organism.

reaction rate. With modification variability, a trait can change within certain limits (range) characteristic of each state of the genotype. The range within which the same genotype is capable of causing the development of different phenotypes is called the reaction norm. In other words, the normreactions - this is the amplitude of the possible variability of the ontogeny of an organism with a specific unchanged genotype. The rate of reaction is best observed in organisms with the same genotypes, such as vegetatively propagating plants and identical twins. In this case, it is possible to identify the norm of the reaction of the genotype in the most "pure" form. The reaction rate controlled by the genotype is the result of an evolutionary process.

The main factors that can ensure the variation of signs within the norm of the reaction are:

1) polygenic determination of the trait and the reaction of the body;

2) pleiotropic action of the gene;

3) the dependence of the manifestation of the mutation on environmental conditions;

4) heterozygosity of the organism;

5) interaction of genes at the level of gene products (subunits of protein molecules);

6) alternative ways of development in the body system and implementation of biosynthesis in the cell (blocking of one way is compensated by another).

Penetrance is characterized by the frequency or probability of manifestation of an allele of a certain gene and is determined by the percentage of individuals in a population in which it is phenotypically manifested. Distinguish between complete (manifestation of a trait in all individuals) and incomplete (in a part) penetrance. Quantitatively, penetrance is expressed as a percentage of individuals in which a given allele is manifested. So, for example, the penetrance of congenital hip dislocation in humans is 25%, which indicates that only 1/4 of the genotypes carrying a certain gene show its phenotypic effect.

At the heart of incomplete penetrance lies the interaction of genetic and environmental causes. Knowledge of the penetrance of certain alleles is necessary in medical genetic counseling to determine the possible genotype of "healthy" people in whose family there were hereditary diseases. Cases of incomplete penetrance include manifestations of genes that control sex-limited and sex-dependent traits.

Expressivity - the degree of phenotypic manifestation of a gene, as a measure of the strength of its action, determined by the degree of development of the trait. Expressivity in both sexes can be the same or different, constant or variable, if the severity of the trait with the same genotype varies from individual to individual. In the absence of variability of the trait controlled by this allele, one speaks of constant expressivity (an unambiguous reaction norm). For example, alleles of ABO blood groups in humans have almost constant expressivity. Another type of expressiveness is changeable or variable. Various reasons lie at the basis: the influence of the conditions of the external environment (modifications), the genotypic environment (during the interaction of genes).

The degree of expressiveness is quantified using statistical indicators. In cases of extreme variants of changes in expressivity (complete absence of a sign), an additional characteristic is used - penetrance. Huntington's chorea can serve as an example of incomplete penetrance and variable expression of the expression of a dominant gene. The age of the first appearance of Huntington's chorea is varied. It is known that in some carriers it will never manifest itself (incomplete penetrance), in addition, this gene has varying expressivity, since carriers become ill at different ages.

Modification variability provides a relatively rapid formation during ontogenesis of the organism's adaptations to changing environmental conditions, thereby contributing to the survival of the organism. Consequently, modifications are the most important factor in the normal course and completion of the ontogeny of a living organism.

Despite the fact that modifications are not inherited by offspring, modification variability in general is important for the evolution of the organic world. Modifications can serve in the course of natural selection as a "cover" for mutations, the phenotypic manifestation of which duplicates non-hereditary changes. Favoring the survival of organisms, modification variability contributes to the preservation and participation in reproduction of specific individuals with diverse genotypes. Along with this, modifications contribute to the development of new habitats by the species (population), which leads to the expansion of the range of this group of organisms. All of these modification effects favor the evolutionary success of a species or population.

Man as a specific object of genetic research. Methods for studying human genetics. Medico-genetic aspect of marriage. Medical genetic counseling. The value of genetics for medicine.

Man as a specific object of genetic research. The study of human genetics is associated with great difficulties: a complex karyotype - many chromosomes and linkage groups, late puberty and a rare change of generations, a small number of offspring, the impossibility of experimentation, the impossibility of creating the same living conditions. Despite all this, human genetics is currently better understood than the genetics of many other organisms (for example, mammals) due to the needs of medicine and a variety of modern research methods.

Study Methods :

genealogical method consists in the study of pedigrees based on the Mendelian laws of inheritance and helps to establish the nature of the inheritance of a trait (dominant or recessive). This is how the inheritance of individual characteristics of a person is established: facial features, height, blood type, mental and mental make-up, as well as some diseases. This method revealed the harmful effects of closely related marriages, which are especially evident when homozygous for the same unfavorable recessive allele. In related marriages, the probability of having children with hereditary diseases and early infant mortality is tens and even hundreds of times higher than the average.

twin method is to study the differences between identical twins. This method is provided by nature itself. It helps to identify the influence of environmental conditions on the phenotype with the same genotypes. Growing up in the same conditions, identical twins have a striking similarity not only in morphological features, but also in mental and intellectual characteristics. Using the twin method, the role of heredity in a number of diseases was revealed.

Population-statistical method. Population genetics studies the genetic differences between individual groups of people (populations), explores the patterns of geographical distribution of genes.

Cytogenetic method . is based on the study of variability and heredity at the level of cells and subcellular structures. A connection has been established for a number of serious diseases with chromosomal abnormalities. Chromosomal disorders occur in 7 out of every thousand newborns, and they also lead to the death of the embryo (miscarriage) in the first third of pregnancy in half of all cases. If a child with chromosomal disorders is born alive, it usually suffers from severe ailments, lags behind in mental and physical development.

Biochemical methods . The content allows you to identify many hereditary human diseases associated with metabolic disorders. Anomalies of carbohydrate, amino acid, lipid and other types of metabolism are known. So, for example, diabetes mellitus is caused by a violation of the normal activity of the pancreas - it does not release the necessary amount of the hormone insulin into the blood, resulting in an increase in blood sugar. This disorder is not caused by a single gross error in genetic information, but by a collection of small errors that collectively lead to or predispose to disease.

Methods of genetics of somatic cells - studies the heredity and variability of somatic cells, i.e. body cells, not sex cells. Somatic cells have a whole set of genetic information; they can be used to study the genetic characteristics of an entire organism. Human somatic cells are obtained for genetic research from biopsy material (vital excision of tissues or organs), when a small piece of tissue is taken for research.

Immunogenetic methods . The immunogenetic method includes serological methods, immunoelectrophoresis, etc., which are used to study blood groups, proteins and enzymes in the blood serum of tissues. It can be used to establish immunological incompatibility, identify immunodeficiency, twin mosaicism, etc.

Molecular genetic methods . Universality of methods. Characterization of the main methodological approaches (DNA isolation, restriction, electrophoresis, blotting, hybridization). Polymerase chain reaction, sequencing. Possibilities and scope of molecular genetic methods in the diagnosis of hereditary pathology.

Methods for studying gene linkage . Fundamentals and conditions for the application of the method in human genetics and medical genetics.

Biological modeling of hereditary diseases studies human diseases on animals that can suffer from these diseases. It is based on Vavilov's law of homologous series of hereditary variability, for example, sex-linked hemophilia can be studied in dogs, epilepsy in rabbits, diabetes mellitus, muscular dystrophy in rats, cleft lip and palate in mice.

Medical genetic counseling - specialized medical care - the most common form of prevention of hereditary diseases. Genetic counseling - consists of informing a person about the risk of developing a hereditary disease, passing it on to offspring, as well as about diagnostic and therapeutic actions.

Stage 1 counseling - clarifying the diagnosis of the disease.

Stage 2 counseling - determination of the risk of having a sick child.

Stage 3 counseling - a geneticist should draw a conclusion about the risk of disease in the examined children and give them appropriate recommendations.

4 (final) stage counseling - the correct answer and the likely complications or outcome of the expected pregnancy in a language accessible to them.

task medical genetics is detection, study, prevention and treatment of hereditary diseases, as well as the development of ways to prevent the harmful effects of environmental factors on human heredity.There are practically no diseases that have absolutely nothing to do with heredity. Conditionally hereditary diseases can be divided into three large groups: metabolic diseases, molecular diseases, which are usually caused by gene mutations, and chromosomal diseases.

Gene mutations can be expressed in an increase or decrease in the activity of certain enzymes, up to their absence. Phenotypically, such mutations manifest themselves as hereditary metabolic diseases, which are determined by the absence or excess of the product of the corresponding biochemical reaction. Gene mutations are classified according to their phenotypic manifestation, i.e., as diseases associated with impaired amino acid, carbohydrate, lipid, mineral metabolism, and nucleic acid metabolism.

Chromosomal diseases. This type of hereditary disease is associated with a change in the number or structure of chromosomes. The frequency of chromosomal abnormalities in newborns is from 0.6 to 1%, and at the stage of 8-12 weeks, about 3% of embryos have them. Among spontaneous miscarriages, the frequency of chromosomal abnormalities is approximately 30%, and in the early stages (up to two months) - 50% and above. In humans, all types of chromosomal and genomic mutations have been described, including aneuploidy, which can be of two types -myosomy and polysomy. Monosomes are especially heavy

Shereshevsky's syndrome - Turner (44+X), manifested in women who are characterized by pathological changes in physique (short stature, short neck), disorders in the development of the reproductive system (absence of most female secondary sexual characteristics), mental limitation. The frequency of occurrence of this anomaly is 1:4000-5000.

Trisomic women (44 + XXX), as a rule, they are distinguished by violations of sexual, physical and mental development, although in some patients these signs may not appear. Cases of fertility of such women are known. The frequency of the syndrome is 1:1000.

Klinefelter syndrome (44+XXY) characterized by impaired development and activity of the gonads, eunuchoid body type (narrower than the pelvis, shoulders, body hair and fat deposition on the body according to the female type, arms and legs elongated compared to the body). Hence the higher growth. These signs, combined with some mental retardation, appear in a relatively normal boy from the time of puberty. Klinefelter's syndrome is observed with polysomy not only on the X chromosome (XXX XXXY, XXXXY), but also on the Y chromosome (XYY.XXYY.XXYYY). The frequency of the syndrome is 1:1000.

Down syndrome ( trisomy on the 21st chromosome) . According to various authors, the birth rate of children with Down syndrome is 1:500-700 newborns, and over the past decades, the frequency of trisomy-21 has increased.

In the case of the birth of a sick child, sometimes its medication, dietary and hormonal treatment is possible. Poliomyelitis can serve as a clear example confirming the possibilities of medicine in the fight against hereditary diseases. This disease is characterized by hereditary predisposition, but the direct cause of the disease is a viral infection. Carrying out mass immunization against the causative agent of the disease made it possible to save all children who are hereditarily predisposed to it from the severe consequences of the disease. Dietary and hormonal treatment has been successfully used in the treatment of phenylketonuria, diabetes mellitus and other diseases.

Ontogeny as a process of realization of hereditary information in certain environmental conditions. The main stages of ontogenesis. Types of ontogenetic development. Periodization of ontogeny.

Ontogenesis, or individual development , is carried out on the basis of a hereditary program obtained through the germ cells of the parents that have entered into fertilization (with asexual reproduction, this program is contained in the non-specialized cells of the only parent that gives offspring). In the course of the implementation of hereditary information in the process of ontogenesis, the organism forms specific and individual morphological, physiological and biochemical properties, in other words - phenotype. In the process of development, the organism naturally changes its characteristics, remaining nonetheless complete system. Therefore, the phenotype should be understood as a set of properties throughout the entire course of individual development, at each stage of which there are its own characteristics.

The leading role in the formation of the phenotype belongs to hereditary information contained in the organism's genotype. At the same time, simple traits develop as a result of a certain type of interaction of the corresponding allelic genes. At the same time, the entire genotype system exerts a significant influence on their formation. The formation of complex traits is carried out as a result of various interactions of non-allelic genes directly in the genotype or products controlled by them. The starting program for the individual development of the zygote also contains the so-called spatial information that determines the anterior-posterior and dorsal-abdominal (dorsoventral) coordinates for the development of structures.

Along with this, the result of the implementation of the hereditary program contained in the genotype of an individual depends to a large extent on the conditions under which this process is carried out. Factors external to the genotype of the environment can promote or hinder the phenotypic manifestation of genetic information, enhance or weaken the degree of such manifestation. Already at the stage of transcription, the expression of individual genes is controlled by the interaction of genetic and non-genetic factors. Consequently, even in the formation of the elementary characteristics of an organism - polypeptides - the genotype as a system of interacting genes and the environment in which it is realized take part.

In the genetics of individual development Wednesday is a complex concept. On the one hand, this is the immediate environment in which individual genes and the genotype as a whole perform their functions. It is formed by the whole set of factors of the internal environment of the body: cellular contents (excluding DNA), the nature of direct intercellular interactions, biologically active substances (hormones). The totality of intraorganismal factors affecting the implementation of the hereditary program is denoted as environment of the 1st order. The factors of this environment have a particularly great influence on the function of the genotype during the period of active shaping processes, primarily in embryogenesis. On the other hand, they single out the concept of the environment, or environments of the 2nd order, as a combination of factors external to the body.

Periodization of ontogeny Individual development is a holistic continuous process in which individual events are interconnected in space and time. There are several schemes of periodization of ontogeny, each of which is the most suitable for solving specific scientific or practical problems.

FROM general biological points of view: pre-reproductive, reproductiveand nsharply productive.

AT pre-reproductive period individual is incapable of reproduction. Its main content lies in the development of a sexually mature phenotype.

Embryonic or embryonic, the period of ontogenesis begins from the moment of fertilization and continues until the embryo exits the egg membranes.

Larval the period in a typical variant is observed in the development of those vertebrates, the embryos of which emerge from the egg membranes and begin to lead an independent lifestyle without reaching the definitive (mature) features of the organization.

metamorphosis consists in the transformation of the larva into a juvenile form.

Juvenile the period begins with the completion of metamorphosis and ends with puberty and the beginning of reproduction.

AT reproductive period the individual performs the function of sexual reproduction.

post-reproductive period associated with the aging of the body and is characterized by a weakening or complete cessation of participation in reproduction.

• Human ontogeny

Antenatal ontogeny:

Germinal or embryonic period. First week after conception.

Embryonic period. The second - the fifth week of pregnancy.

Fetal period. 32 weeks.

Postnatal ontogeny:

Neonatal or neonatal period. 1-10 days.

Breast age. 10 days - 1 year.

Early childhood. 1-3 years.

First childhood. 4-7 years old.

Second childhood. 8-12 years for boys, 8-11 years for girls.

Adolescence. 13-16 years for boys, 12-15 years for girls.

Youthful age. 17-21 years old for boys, 16-20 years old girls.

Mature age:

Iperiod: 22-35 years old men, 21-35 years old women.

IIperiod: 36-60 years old men, 36-55 years old women.

Elderly age. Men 61-74 years old, women 56-74 years old.

old age. 75-90 years old.

Longevity period. Over 90 years.

The germinal period is the time from the beginning of conception to the formation of the embryo. The embryonic period is divided into 2 phases: the phase of histotrophic nutrition and the phase of yolk circulation. In the fetal period, there is a transition from yolk to hemo-amniotrophic nutrition. In the neonatal period, the baby feeds on colostrum milk. During the period of breastfeeding mature, and then complementary foods are connected to mother's milk and the sensorimotor scheme of standing is realized. During the period early childhood learning to walk and speak. Increases in early childhood vocabulary and the first phase of the formation of thinking proceeds. In the second childhood, the analytical and synthetic activity of the brain becomes more complicated and the 2nd phase of thinking is formed. In adolescence, the maturation of visceral systems is basically completed and the 3rd phase of the organization of thinking proceeds. The period of adolescence or adolescent is a turning point, when the formation of personality and puberty is completed. The period of maturity or stability is the most productive in social terms and the organization of physiological functions. In the period of old age, involutional changes begin, which are the result of physiological rearrangements of homeostasis.In subsequent periods, they are activated

Correlation of onto- and phylogenesis. The law of germinal similarity of K. Baer. Biogenetic law of E. Haeckel and F. Müller

1st Law of germinal resemblance "Early stages of development of organisms belonging to different classes more similar to each other than the later stages.

2nd Law of Development Specialization “In the process of ontogenesis, each organism develops more and more specific features”

F. Müller: "Evolutionary changes in the structureadultsanimals come fromchange in the course of ontogenesis of descendantscompared to those of their ancestors.

E. Haeckel Created a triple parallelism method:

comparative morphology

comparative embryology data

paleontological data

sources for constructing a phylogenetic series

biogenetic law"Ontogeny is a quick and short repetition of phylogeny"

Recapitulation -this is a repetition in the ontogeny of the descendants of the stages of evolution of their ancestors.

• The ratio of onto- and phylogenesis . According to modern concepts, most phylogenetic innovations are associated with ontogenetic heterochronies, that is, with shifts in the relative rates of various ontogenetic processes. One of the evolutionarily most significant heterochronies is the shift in the period of puberty in evolutionary descendants to stages corresponding to the larvae of their ancestors. This shift is called neoteny, or paedomorphosis. In this case, the life cycle of evolutionary descendants is usually shortened (for example, due to the loss of the phase of metamorphosis inherent in the ancestors). Neoteny is considered one of the ways to achieve rapid evolutionary progress.

  Further development of the problems of ontogenesis is of paramount importance both for fundamental natural science and for a number of medical, biotechnological and environmental problems.

Characteristics and significance of the main stages of embryonic development: prezygotic period, fertilization, zygote, crushing. Their regulatory mechanisms at the gene and cellular levels.

• Fertilization - it is the process of fusion of sex cells. The diploid cell resulting from fertilizationzygote -represents First stage development of a new organism. The fertilization process consists of three successive phases:

  a) convergence of gametes (gamons(hormones of gametes), on the one hand, activate the movement of spermatozoa, and on the other hand, their gluing.) At the moment of contact of the spermatozoon with the egg membrane,acrosome reaction,during which, under the action of proteolytic enzymes, the acrosomes dissolve the egg membranes. Further, the plasma membranes of the egg and sperm merge and through the resulting cytoplasmic bridge of the cytoplasm of both gametes are combined. Then the nucleus and centriole of the spermatozoon pass into the cytoplasm of the egg, and the spermatozoon membrane is embedded in the membrane of the egg cell. The tail part of the sperm in most animals also enters the egg, but then separates and dissolves, without playing any role in further development;

  b) activation of the egg Due to the fact that the section of the spermatozoon membrane is permeable to sodium ions, the latter begin to enter the egg, changing the membrane potential of the cell. Then, in the form of a wave propagating from the point of contact of the gametes, an increase in the content of calcium ions occurs, followed by the dissolution of cortical granules as a wave. The specific enzymes released at the same time contribute to the detachment of the yolk membrane; she hardens itfertilization shell.All the described processes are the so-calledcortical reaction.;

  c) fusion of gametes, or syngamy The egg at the time of the meeting with the sperm is usually at one of the stages of meiosis, blocked by a specific factor. In most vertebrates, this block occurs at the stage of metaphase II; in many invertebrates, as well as in three species of mammals (horses, dogs and foxes), the block occurs at the stage of diakinesis. In most cases, the meiotic block is removed after the activation of the egg due to fertilization. While meiosis is completed in the egg, the nucleus of the sperm that has penetrated into it is modified. It takes the form of an interphase and then a prophase nucleus. During this time, DNA doubles andmale pronucleusreceives the amount of hereditary material corresponding toP2 With,those. contains a haploid set of reduplicated chromosomes. The nucleus of the ovum that has completed meiosis becomesfemale pronucleus,also acquiringP2 With.Both pronuclei make complex movements, then approach and merge (syncarion) , forming a common metaphase plate. This, in fact, is the moment of the final fusion of gametes -syngamy.The first mitotic division of the zygote leads to the formation of two embryonic cells (blastomeres) with a set of chromosomes 2n2 cin everyone.

  Zygote - diploid(containing a complete double setchromosomes) a cell resulting fromfertilization(mergerseggsandsperm). The zygote istotipotent(that is, capable of generating any other)cell.

  Man's firstmitoticdivision of the zygote occurs approximately 30 hours after fertilization, which is due to the complex processes of preparation for the first act of crushing. Cells formed as a result of crushing the zygote are called

  blastomeres. The first divisions of a zygote are called "crushing" because the cell is crushed: after each division, the daughter cells become smaller and smaller, and there is no stage of cell growth between divisions.

  Splitting up - this is a series of successive mitotic divisions of the zygote and further blastomeres, ending in the formation of a multicellular embryo -blastula. Between successive divisions, cell growth does not occur, but DNA is necessarily synthesized. All DNA precursors and necessary enzymes are accumulated during oogenesis. First, blastomeres are adjacent to each other, forming a cluster of cells calledmorula . Then a cavity is formed between the cells -blastocoel, filled with liquid. Cells are pushed to the periphery, forming the wall of the blastula -blastoderm. The total size of the embryo by the end of cleavage at the blastula stage does not exceed the size of the zygote. The main result of the crushing period is the transformation of the zygote intomulticellular unilamellar embryo .

  Morphology of crushing. As a rule, blastomeres are arranged in a strict order relative to each other and the polar axis of the egg. The order, or method, of crushing depends on the amount, density and distribution of the yolk in the egg. According to the rules of Sachs-Hertwig, the cell nucleus tends to be located in the center of the cytoplasm free from yolk, and the spindle of cell division - in the direction of the greatest extent of this zone.

  In oligo- and mesolecithal eggs crushingcomplete,orholoblastic.This type of crushing is found in lampreys, some fish, all amphibians, as well as in marsupials and placental mammals. With complete crushing, the plane of the first division corresponds to the plane of bilateral symmetry. The plane of the second division runs perpendicular to the plane of the first. Both furrows of the first two divisions are meridian, i.e. start at the animal pole and spread to the vegetative pole. The egg cell is divided into four more or less equal in size blastomeres. The plane of the third division runs perpendicular to the first two in the latitudinal direction. After that, in mesolecithal eggs at the stage of eight blastomeres, uneven crushing is manifested. At the animal pole there are four smaller blastomeres -micrometers,on the vegetative - four larger ones -macromers.Then the division again goes in the meridian planes, and then again in the latitudinal.

  In polylecithal oocytes of bony fish, reptiles, birds, as well as monotreme mammals, crushingpartial,ormeroblastic,those. covers only the cytoplasm free from yolk. It is located in the form of a thin disk at the animal pole, therefore this type of crushing is calleddiscoidal.When characterizing the type of crushing, the relative position and rate of division of blastomeres are also taken into account. If blastomeres are arranged in rows one above the other along the radii, crushing is calledradial.It is typical of chordates and echinoderms. In nature, there are other variants of the spatial arrangement of blastomeres during crushing, which determines such types of it as spiral in mollusks, bilateral in ascaris, anarchic in jellyfish.

  A relationship was noted between the distribution of the yolk and the degree of synchronism in the division of animal and vegetative blastomeres. In oligolecithal eggs of echinoderms, cleavage is almost synchronous; in mesolecithal egg cells, synchrony is disturbed after the third division, since vegetative blastomeres due to a large number yolks divide more slowly. For forms with partial fragmentation, divisions are asynchronous from the very beginning andblastomeres occupying a central position divide faster.

  By the end of crushing, a blastula is formed. The type of blastula depends on the type of crushing, and therefore on the type of egg.

  Features of molecular-genetic and biochemical processes during crushing. As noted above, mitotic cycles during the cleavage period are greatly shortened, especially at the very beginning.

  For example, the entire fission cycle in sea urchin eggs lasts 30-40 minutes, while the duration of the S-phase is only 15 minutes. GI- andG2-periods are practically absent, since the necessary supply of all substances has been created in the cytoplasm of the egg cell, and the greater, the larger it is. Before each division, the synthesis of DNA and histones occurs.

  The rate at which the replication fork moves along the DNA during cleavage is normal. At the same time, there are more points of initiation in the DNA of blastomeres than in somatic cells. DNA synthesis occurs in all replicons simultaneously, synchronously. Therefore, the time of DNA replication in the nucleus coincides with the doubling time of one, moreover, shortened, replicon. It was shown that when the nucleus is removed from the zygote, cleavage occurs and the embryo in its development reaches almost the blastula stage. Further development stops.

  At the beginning of cleavage, other types of nuclear activity, such as transcription, are practically absent. In different types of eggs, gene transcription and RNA synthesis begin at different stages. In cases where there are many different substances in the cytoplasm, as, for example, in amphibians, transcription is not activated immediately. RNA synthesis in them begins at the stage of early blastula. On the contrary, in mammals, RNA synthesis already begins at the stage of two blastomeres.

  During the cleavage period, RNA and proteins are formed, similar to those synthesized during oogenesis. These are mainly histones, cell membrane proteins and enzymes necessary for cell division. These proteins are used immediately along with the proteins stored earlier in the cytoplasm of the oocytes. Along with this, during the period of crushing, the synthesis of proteins is possible, which was not there before. This is supported by data on the presence of regional differences in the synthesis of RNA and proteins between blastomeres. Sometimes these RNAs and proteins come into action at a later stage.

  An important role in crushing is played by the division of the cytoplasm -cytotomy.It has a special morphogenetic significance, since it determines the type of crushing. In the process of cytotomy, a constriction is first formed with the help of a contractile ring of microfilaments. The assembly of this ring takes place under the direct influence of the poles of the mitotic spindle. After cytotomy, the blastomeres of oligolecithal eggs remain connected to each other only by thin bridges. It is at this time that they are easiest to separate. This is because cytotomy leads to a decrease in the contact zone between cells due to the limited surface area of ​​the membranes. Immediately after cytotomy, the synthesis of new sections of the cell surface begins, the contact zone increases, and blastomeres begin to tightly touch. Cleavage furrows run along the boundaries between individual sections of the ovoplasm, reflecting the phenomenon of ovoplasmic segregation.Therefore, the cytoplasm of different blastomeres differs in chemical composition.

Characteristics and significance of the main stages of embryonic development: gastrulation, histo- and organogenesis. Formation of 2 and 3 layer embryos. Methods of formation of the mesoderm. Derivatives of the germ layers. Regulatory mechanisms of these processes at the gene and cellular levels.

• Histogenesis - (from the Greek. histos - tissue it ... genesis), a set of processes that has developed in phylogenesis, ensuring the formation, existence and restoration of tissues with their inherent organ-specific features in the ontogenesis of multicellular organisms. features. In the body, tissues develop from certain embryonic rudiments (derivative germ layers) formed as a result of proliferation, movement (morphogenetic movements) and adhesion of embryonic cells at the early stages of its development in the process of organogenesis. Beings, G.'s factor - the differentiation of the determined cells leading to emergence of various morfol. and physiol. types of cells that are regularly distributed in the body. Sometimes G. is followed by formation of intercellular substance. An important role in determining the direction of G. belongs to intercellular contact interactions and hormonal influences. The set of cells that perform a certain G., is subdivided into a number of groups: ancestral (stem) cells capable of differentiation and replenishment of the loss of their own kind by division; progenitor cells (the so-called semi-stem cells) - differentiate, but retain the ability to divide; mature diff. cells. Reparative G. in the postnatal period underlies the restoration of damaged or partially lost tissues. Qualities, G.'s changes can lead to emergence and growth of a tumor.

  Organogenesis (from Greek.organon- organ,genesis- development, education) - the process of development, or formation, of organs in the embryo of humans and animals. Organogenesis follows the earlier periods of embryonic development (see Embryo) - egg crushing, gastrulation, and occurs after the main rudiments (anlages) of organs and tissues are isolated. Organogenesis proceeds in parallel with histogenesis (see), or tissue development. Unlike tissues, each of which has one of the embryonic rudiments as its source, organs, as a rule, arise with the participation of several (from two to four) different rudiments (see Germ layers), giving rise to different tissue components of the organ. For example, as part of the intestinal wall, the epithelium lining the organ cavity and the glands develop from the inner germ layer - the endoderm (see), the connective tissue with vessels and smooth muscle tissue - from the mesenchyme (see), the mesothelium covering the serous membrane of the intestine, - from the visceral leaf of the splanchnotome, i.e., the middle germinal leaf - the mesoderm, and the nerves and ganglia of the organ - from the neural rudiment. The skin is formed with the participation of the outer germ layer - ectoderm (see), from which the epidermis and its derivatives develop (hair, sebaceous and sweat glands, nails, etc.), and dermatomes, from which mesenchyme arises, differentiating into the connective tissue basis of the skin (dermis ). Nerves and nerve endings in the skin, as elsewhere, are derivatives of the neural germ. Some organs are formed from one germ, for example, bone, blood vessels, lymph nodes - from mesenchyme; however, here, too, derivatives of the rudiment of the nervous system - nerve fibers - grow into the anlage, and nerve endings are formed.

  If histogenesis consists mainly in the reproduction and specialization of cells, as well as in the formation of intercellular substances and other non-cellular structures, then the main processes underlying organogenesis are the formation of germ layers of folds, protrusions, protrusions, thickenings, uneven growth, fusion or division (separation), as well as the mutual germination of various bookmarks. In humans, organogenesis begins at the end of the 3rd week and ends in general terms by the 4th month of intrauterine development. However, the development of a number of provisional (temporary) organs of the embryo - chorion, amnion, yolk sac - begins already at the end of the 1st week, and some definitive (final) organs form later than others (for example, lymph nodes - starting from the last months of intrauterine development and up to the onset of puberty).

  Gastrulation - single-layer embryo - blastula - turns intomultilayer -two- or three-layer, calledgastrula(from Greek.gaster -stomach in a diminutive sense).

  In primitive chordates, for example, in the lancelet, a homogeneous single-layer blastoderm during gastrulation is transformed into an outer germ layer - ectoderm - and an inner germ layer -endoderm.The endoderm forms the primary intestine with a cavity insidegastrocoel.The hole leading to the gastrocoel is calledblastoporeor primary mouth.Two germ layersare defining morphological signs of gastrulation. Their existence at a certain stage of development in all multicellular animals, from the coelenterates to the higher vertebrates, allows us to think about the homology of the germ layers and the unity of the origin of all these animals. In vertebrates, in addition to the two mentioned, during gastrulation, a third germ layer is formed -mesoderm,located between the ecto- and endoderm. The development of the middle germ layer, which is a chordomesoderm, is an evolutionary complication of the gastrulation phase in vertebrates and is associated with an acceleration of their development at the early stages of embryogenesis. In more primitive chordates, such as the lancelet, chordomesoderm usually forms at the beginning of the phase following gastrulation -organogenesis.The shift in the time of development of some organs relative to others in descendants compared with ancestral groups is a manifestation ofheterochrony.Changes in the timing of the formation of the most important organs in the course of evolution are not uncommon.

  The process of gastrulation is characterizedimportant cellular transformations,such as directed movements of groups and individual cells, selective propagation and sorting of cells, the beginning of cytodifferentiation and induction interactions.

  Gastrulation methods different. Four types of spatially directed cell movements are distinguished, leading to the transformation of the embryo from a single layer to a multilayer one.

  Intussusception - invagination of one of the sections of the blastoderm inward as a whole layer. In the lancelet, cells of the vegetative pole invaginate; in amphibians, intussusception occurs on the border between the animal and vegetative poles in the region of the gray crescent. The process of invagination is possible only in eggs with a small or medium amount of yolk.

  epiboly - fouling with small cells of the animal pole of larger, lagging in the rate of division and less mobile cells of the vegetative pole. This process is clearly expressed in amphibians.

  Denomination - stratification of blastoderm cells into two layers lying one above the other. Delamination can be observed in the discoblastula of embryos with a partial type of crushing, such as reptiles, birds, and oviparous mammals. Delamination manifests itself in the embryoblast of placental mammals, leading to the formation of hypoblast and epiblast.

  Immigration - movement of groups or individual cells that are not united into a single layer. Immigration occurs in all embryos, but is most characteristic of the second phase of gastrulation in higher vertebrates. In each specific case of embryogenesis, as a rule, several methods of gastrulation are combined.

  Morphology of gastrulation. In the region of the blastula, from the cellular material of which, during gastrulation and early organogenesis (neurulation), completely defined germ layers and organs are usually formed. Invagination begins at the vegetative pole. Due to faster division, the cells of the animal pole grow and push the cells of the vegetative pole into the blastula. This is facilitated by a change in the state of the cytoplasm in the cells that form the lips of the blastopore and adjacent to them. Due to invagination, the blastocoel decreases and the gastrocoel increases. Simultaneously with the disappearance of the blastocoel, the ectoderm and endoderm come into close contact. In the lancelet, as in all deuterostomes (they include the echinoderm type, the chordate type, and some other small types of animals), the blastopore region turns into the tail part of the organism, in contrast to protostomes, in which the blastopore corresponds to the head part. The mouth opening in deuterostomes is formed at the end of the embryo opposite the blastopore. Gastrulation in amphibians has much in common with the gastrulation of the lancelet, but since the yolk in their eggs is much larger and it is located mainly at the vegetative pole, large amphiblastula blastomeres are not able to bulge inward.Intussusception goes a little differently. On the border between the animal and vegetative poles in the region of the gray sickle, the cells first strongly stretch inward, taking the form≪ flask-shaped≫ , and then pull the cells of the surface layer of the blastula along with them. A crescent groove and a dorsal blastopore lip appear. At the same time, smaller cells of the animal pole, dividing faster, begin to move towards the vegetative pole. In the region of the dorsal lip, they turn up and invaginate, and larger cells grow on the sides and on the side opposite the sickle-shaped groove. Then the processepiboly leads to the formation of the lateral and ventral lips of the blastopore. The blastopore closes into a ring, inside which large light cells of the vegetative pole are visible for some time in the form of the so-called yolk plug. Later, they are completely immersed inward, and the blastopore narrows. Using the method of marking with vital (vital) dyes in amphibians, the movements of blastula cells during gastrulation have been studied in detail. It has been established that specific areas of the blastoderm, calledpresumptive(from lat. praesumptio - assumption), with normal development, they first appear in the composition of certain rudiments of organs, and then in the composition of the organs themselves. It is known that in tailless amphibians the material of the presumptive notochord and mesoderm at the blastula stage lies not on its surface, but in the inner layers of the amphiblastula wall, however, at approximately the same levels as shown in the figure. An analysis of the early stages of amphibian development allows us to conclude thatovoplasmic segregation,which is clearly manifested in the egg and zygote is of great importance in determining the fate of cells that have inherited one or another section of the cytoplasm. Gastrulation in embryos with a meroblastic type of cleavage and development has its own characteristics. Atbirdsit begins after the cleavage and formation of the blastula during the passage of the embryo through the oviduct. By the time the egg is laid, the embryo already consists of several layers: the top layer is calledepiblast,lower -primary hypoblast.Between them is a narrow gap - the blastocoel. Then formedsecondary hypoblast,the mode of formation of which is not entirely clear. There is evidence that the primary germ cells originate in the primary hypoblast of birds, while the secondary forms the extraembryonic endoderm. The formation of primary and secondary hypoblast is considered as a phenomenon preceding gastrulation. The main events of gastrulation and the final formation of the three germ layers begin after oviposition with the onset of incubation. There is an accumulation of cells in the posterior part of the epiblast as a result of the uneven speed of cell division and their movement from the lateral parts of the epiblast to the center, towards each other. The so-calledprimary line,which extends towards the head end. In the center of the primary streak is formedprimary furrow,and along the edges - primary rollers. A thickening appears at the head end of the primary strip -Hensen knot,and in it - the primary fossa. When epiblast cells enter the primary groove, their shape changes. They resemble in shape≪ flask-shaped≫ amphibian gastrula cells. These cells then become stellate and sink under the epiblast to form the mesoderm. The endoderm is formed on the basis of the primary and secondary hypoblast with the addition of a new generation of endodermal cells migrating from the upper layers, the blastoderm. The presence of several generations of endodermal cells indicates the prolongation of the gastrulation period in time. Part of the cells migrating from the epiblast through the Hensen's knot forms the future notochord. Simultaneously with the initiation and elongation of the chord, the Hensen's node and the primary streak gradually disappear in the direction from the anterior to the caudal end. This corresponds to the narrowing and closure of the blastopore. As the primary streak contracts, it leaves behind the formed sections of the axial organs of the embryo in the direction from the head to the tail sections. It seems reasonable to consider the movements of cells in the chick embryo as homologous epiboly, and the primary streak and Hensen's knot as homologous to the blastopore in the dorsal lip of the amphibian gastrula. It is interesting to note that the cells of mammalian embryos, despite the fact that in these animals the eggs have a small amount of yolk, and fragmentation is complete, in the gastrulation phase they retain the movements characteristic of the embryos of reptiles and birds. This confirms the idea of ​​the origin of mammals from an ancestral group whose eggs were rich in yolk.

  Features of the stage of gastrulation. Gastrulation is characterized by a variety of cellular processes. Mitotic continuescell reproduction,moreover, it has different intensity in different parts of the embryo. However, the most feature gastrulation consists ofmovement of cell masses.This leads to a change in the structure of the embryo and its transformation from blastula to gastrula. going onsortingcells according to their belonging to different germ layers, inside which they≪ get to know≫ each other. The gastrulation phase beginscytodifferentiation,which means the transition to the active use of the biological information of one's own genome. One of the regulators of genetic activity is the different chemical composition of the cytoplasm of embryonic cells, which is established as a result of ovoplasmic segregation. So, the ectodermal cells of amphibians have a dark color due to the pigment that got into them from the animal pole of the egg, and the endoderm cells are light, since they come from the vegetative pole of the egg. During gastrulation, the role is very largeembryonic induction.It has been shown that the appearance of the primary streak in birds is the result of an inductive interaction between the hypoblast and the epiblast. The hypoblast has polarity. A change in the position of the hypoblast relative to the epiblast causes a change in the orientation of the primitive streak. All of these processes are described in detail in the chapter. It should be noted that these manifestationsintegritygerm likedetermination, embryonic regulationandintegrationinherent in him during gastrulation to the same extent as during crushing.

  The formation of the mesodermIn all animals, with the exception of coelenterates, in connection with gastrulation (in parallel with it or at the next stage, due to gastrulation) occurs and third germ layer - mesoderm. This is a collection of cellular elements that lie between the ectoderm and endoderm, i.e., in the blastocele. Like this. Thus, the embryo becomes not two-layered, but three-layered. In higher vertebrates, the three-layer structure of the embryos arises already in the process of gastrulation, while in the lower chordates and in all other types, as a result of gastrulation itself, a two-layer embryo is formed.

  Two fundamentally different ways of the appearance of mesoderm can be established: teloblastic, characteristic protostomia, and enterocoelous, characteristic ofDeute rosiomia. in protostomes during gastrulation, on the border between the ectoderm and endoderm, on the sides of the blastopore, there are already two large cells that separate small cells from themselves (due to divisions). Thus, the middle layer is formed - mesoderm. Teloblasts, giving new and new generations of mesoderm cells, remain at the posterior end of the embryo. For this reason, this method of mesoderm formation is called teloblastic (from Greek telos - end).

  With the enterocoel method, the totality of cells of the emerging mesoderm appears in the form of pocket-like protrusions of the primary intestine (protrusion of its walls into the blastocoel). These protrusions, inside which parts of the primary intestinal cavity enter, are isolated from the intestine and separated from it in the form of sacs. The cavity of the sacs turns into in general, i.e., into the secondary body cavity, the coelomic sacs can be subdivided into segments of the middle germ layer, which does not reflect the whole variety of variations and deviations that are strictly regular for individual groups of animals. Similar to teloblastic, but only outwardly, the method of mesoderm formation is not by dividing teloblasts, but by the appearance of an unpaired dense primordium (group of cells) at the edges of the blastopore, which subsequently divides into two symmetrical stripes of cells. With the enterocele method, the mesoderm primordium can be paired or unpaired; in some cases, two symmetrical coelomic sacs are formed, while in others, one common coelomic sac is first formed, which subsequently divides into two symmetrical halves.

  Derivatives of the germ layers. The further fate of the three germ layers is different.

  From the ectoderm develop: all nervous tissue; the outer layers of the skin and its derivatives (hair, nails, tooth enamel) and partially the mucous membrane of the oral cavity, nasal cavities and anus.

  Endoderm gives rise to the lining of the entire digestive tract - from the oral cavity to the anus - and all its derivatives, i.e. thymus, thyroid, parathyroid glands, trachea, lungs, liver and pancreas.

  From the mesoderm are formed: all types connective tissue, bone and cartilage tissue, blood and vascular system; all types muscle tissue; excretory and reproductive systems, dermal layer of the skin.

  In an adult animal, there are very few organs of endodermal origin that do not contain nerve cells derived from the ectoderm. Each important organ also contains derivatives of the mesoderm - blood vessels, blood, and often muscles, so that the structural isolation of the germ layers is preserved only at the stage of their formation. Already at the very beginning of their development, all organs acquire a complex structure, and they include derivatives of all germ layers

Postembryonic period of ontogeny. Main processes: growth, formation of definitive structures, puberty, reproduction, aging.

• Postnatal ontogeny - the period of development of the body from birth to death. It combines two stages: a) the stage of early postnatal ontogenesis; b) the stage of late postnatal ontogenesis. Early postnatal ontogenesis begins with the birth of the organism and ends with the onset of the structural and functional maturity of all organ systems, including reproductive system. Its duration in humans is 13-16 years. Early postnatal ontogenesis may include the main processes of organogenesis, differentiation, and growth (for example, in kangaroos) or only growth, as well as differentiation of later maturing organs (sex glands, secondary sexual characteristics). In many animals in postembryonic development, metamorphosis takes place. Late postnatal ontogeny includes adulthood, aging, and death. Postembryonic development is characterized by: 1) intensive growth; 2) the establishment of definitive (final) proportions of the body; 3) the gradual transition of organ systems to functioning in a mode characteristic of a mature organism.

  Growth - this is an increase in the mass and linear dimensions of an individual (organism) due to an increase in mass, but mainly the number of cells, as well as non-cellular formations. To describe growth, growth curves are used (changes in body weight or length during ontogenesis), indicators of absolute and relative growth over a certain period of time, and specific growth rate.

  The growth of an individual is characterized by eitherisometry - uniform growth of parts and organs of the body, orallometry - uneven growth of body parts.allometry it can be negative (for example, slow growth of the head in relation to the body in a child) and positive (for example, accelerated growth of horns in ruminants). Growth rate usually decreases with age. Animals with indefinite growth grow throughout their lives (mollusks, crustaceans, fish, amphibians). In animals with a certain height, growth stops at a certain age (insects, birds, mammals). However, there is no sharp line between definite and indefinite growth. Man, mammals, birds after the cessation of growth can still increase somewhat in size. Growth processes are controlled by the genotype, while simultaneously depending on environmental conditions. Human growth, determined by a combination of hereditary and environmental factors, reveals variability (age, sex, group, intragroup or individual and epochal). On the growth and development of the organism, its genotype can also have an indirect effect through the synthesis of biologically active substances - hormones. These are neurosecrets produced by nerve cells, hormones of the endocrine glands. Hormones can influence both metabolic processes (biosynthesis) and the expression of other genes, which in turn affect growth. Between all endocrine glands there is a relationship regulated by the principle of feedback. So, pituitary hormones affect the endocrine function of the sex glands, thyroid gland and adrenal glands. The pituitary gland produces somatotropic hormone, the lack of which leads to dwarfism - dwarfism, and the excess - to gigantism.

  4th stage of embryogenesis - the stage of definitive (final) organogenesis where permanent organs are formed. Very complex processes occurring at this final stage of embryogenesis are the object of study of private embryology. In this section, we confine ourselves to considering the "fate" of the primary organs of the embryo.

  From the ectoderm develop: the epidermis of the skin and its derivatives - feathers, hair, nails, skin and mammary glands, the nervous system. The anterior (expanded) section of the neural tube is converted into the brain, the rest of it (anterior and middle sections) - into the spinal cord. The endoderm gives rise to the inner lining of the digestive and respiratory systems, the secreting cells of the digestive glands. Somites undergo the following transformations: dermatome forms the dermis (deep layer of the skin); sclerotome is involved in the formation of the skeleton (cartilaginous, then bone); The myotome gives rise to skeletal muscles. Urinary organs develop from the nephrotome.

  Non-segmented mesoderm (splanchnotome) gives rise to the pleura, peritoneum, pericardium, participates in the development of the cardiovascular and lymphatic systems.

  Puberty - the process of formation of the reproductive function of the human body, manifested by the gradual development of secondary sexual characteristics and culminating in the onset of puberty. In humans, the period of puberty is called transitional, or puberty, its duration is on average about 5 years. The age limits of puberty are subject to individual fluctuations (for girls from 8 - 10 to 16 - 17 years, for boys from 10 - 12 to 19 - 20 years). The appearance of secondary sexual characteristics in girls from 8 to 10 years old, in boys from 10 to 12 years old is called early puberty (it is usually associated with constitutional factors).

  An important sign of pubertal development - the establishment of regular activity of the gonads, which is manifested in girls by menstruation, and in boys - by ejaculations. The intrasecretory activity of the gonads in both sexes is also manifested by phase changes in the growth rates of individual segments of the skeleton, resulting indefinitive (structures) proportions of the body are established and secondary sexual characteristics are formed. Secondary sexual characteristics include mainly changes in the skin (in particular, the scrotum) and its derivatives (it is during the period of maturation that the mane grows in a lion, the development of the so-called genital skin in monkeys, and horns in a deer). The first signs of pubertal development in boys, along with an increase in the size of the testicles and an acceleration of total growth, are the intensification of hair growth and changes in the scrotum. The average age period for the appearance of individual signs in 50% of the examined was: voice mutation - 12 years 3.5 months, pubic hair growth - 12 years 9.5 months, enlargement of the thyroid cartilage of the larynx - 13 years 3.5 months, axillary hair growth - 13 years 9.5 months and facial hair - 14 years 2 months. Studying the duration and rate of formation of secondary sexual characteristics, V. G. Sidamon Eristavi found that the rate of development of individual signs of puberty has its “peaks”.

  Human reproductive function - reproduction of their own kind. The ability of a person as a species to transfer one half of the genetic information of the future generation from father to mother is provided by the physiological characteristics of the reproductive function of the male body. The reproductive function of the female body ensures the process of fertilization, intrauterine development of the fetus, the birth of a child and breastfeeding. Distinctive feature The reproductive function of a person from other physiological functions of the body is that its normal functioning leads to the fusion of germ cells of male and female organisms in the process of sexual reproduction. Oocytes and spermatozoa are called female and male reproductive cells, or gametes. Male and female gametes in the mature form contain a haploid number of chromosomes, that is, half the normal number. The haploid number of chromosomes in gametes is formed in the process of spermatogenesis and oogenesis (Fig. 16.1). In the male body, meiotic division of spermatogenic cells occurs continuously throughout life after the onset of puberty (puberty). On the contrary, in the oocyte, the haploid number of chromosomes is formed immediately before ovulation of the egg from the follicle. As a result of the ability of the oocyte and sperm to combine with each other during fertilization, a zygote is formed in the female genital tract. This process is called fertilization. The zygote contains a diploid number of chromosomes, as in any somatic cell of the human and animal body. Two chromosomes from the diploid number in the zygote, namely the sex X and Y chromosomes, determine the male or female sex of the future individual in the new generation. The female germ cell contains only X chromosomes, while the male sex cell contains X and Y chromosomes. Chromosomes contain genes that pass on the genetic characteristics of one generation to the next.

  Aging - this is an irreversible process of gradual inhibition of the main functions of the body (regenerative, reproductive, etc.), as a result of which the body loses the ability to maintain homeostasis, withstand stress, illness and injury, which makes death inevitable.

Basic concepts in developmental biology (preformism and epigenesis hypotheses). Modern ideas about the mechanisms of embryonic development.