The word "phenotype" is of Greek origin and is translated (literally) as "discover", "reveal". What is the practical significance of this concept?

What is a phenotype? Definition

A phenotype should be understood as a set of characteristics that are inherent in an individual at a specific stage of development. This set is formed on the basis of the genotype. Diploid organisms are characterized by the manifestation. More precisely, defining what a phenotype is, we should talk about the totality of internal and external characteristics of the organism that were acquired in the process

General information

Despite the fairly accurate phenotype, its concept has a number of uncertainties. Most of the structures and molecules that are encoded by genetic material are not found in the external appearance of the organism. Moreover, they are part of the phenotype. An example is the blood phenotype of humans. In this regard, according to a number of authors, the definition should include those characteristics that can be obtained using diagnostic, medical or technical procedures. A more radical further expansion may include acquired behavior, and, if necessary, the influence of the organism on the environment and other organisms. So, for example, incisors can be taken for their phenotype.

Main characteristics

When defining what a phenotype is, we can talk about some “carrying out” of genetic information towards environmental factors. As a first approximation, two characteristics should be considered:

1. Dimensions of the phenotype. This sign indicates the number of “removal” directions, which characterizes the number of environmental factors.
2. The second sign indicates the level of sensitivity of the phenotype to environmental conditions. This degree is called range.

Taken together, these characteristics indicate the richness and variety of the phenotype. The more multidimensional the set of individual characteristics, the more sensitive the traits and the further they are from the genotype, the richer it is. So, for example, if you compare the phenotype of a bacterium, roundworm, frog, or human, then the “richness” in this chain increases. This means that the human phenotype is richer.

Historical reference

In 1909, Wilhelm Johansen (a Danish scientist) for the first time, in conjunction with the concept of genotype, proposed a definition of phenotype. This made it possible to distinguish heredity from the result of its implementation. The idea of ​​differences can also be traced back to the work of Mendel and Weissmann. At the same time, the latter distinguished somatic and reproductive cells in The chromosome set received from the parents is contained in Chromosomes carry a complex of genes characteristic of a particular species in general and a particular organism in particular. Genes contain information about proteins that can be synthesized, as well as about the mechanisms that, in fact, determine and regulate synthesis. What happens then? During ontogenesis, genes are sequentially turned on and the proteins encoded by them are synthesized. As a result, the formation and development of all the properties and characteristics of the organism that make up its phenotype occurs. In other words, a certain “product” is obtained from the implementation of the genetic program contained in the genotype.

The influence of external conditions on the development of individual characteristics

It should be noted that the genotype is not a clear factor determining the phenotype. To one degree or another, the formation of a set of individual characteristics will also depend on the environment, that is, on external factors. In different conditions, phenotypes have sharp differences. For example, the species of butterflies "Arashnia" produces two offspring per year. Those individuals that emerged from overwintered pupae (spring ones) differ sharply from those that emerged in the summer. The phenotype of the plant may also differ. For example, in open space pine trees are spreading, but in the forest they are slender and tall. In the water buttercup, the shape of the leaf depends on where it is located - in the air or in the water.

Relationships between phenotypes and genotypes

The ability to change, which is provided by the genetic program, is called the reaction norm. As a rule, the more diverse the conditions in which a species lives, the wider this norm. In the case when the environment differs sharply from the one to which the species is adapted, a disruption occurs in the development of organisms and they die. Phenotype traits do not always reflect recessive alleles. But at the same time they are preserved and can be passed on to offspring. This information allows us to better understand the evolutionary process. Only phenotypes are involved, while genotypes are transmitted to the offspring and remain further in the population. The interaction is not limited to the relationship between recessive and dominant alleles - many genes interact with each other.

Genome. Genotype. Phenotype.

1. Phenotype as a result of the implementation of a genotype in a certain environment.
2. Quantitative and qualitative specificity of the manifestation of genes in traits.
3. Interaction of nonallelic genes.

Genome– a set of genes characteristic of the haploid set of chromosomes of a given species. During fertilization, the genomes of the parents combine to form the cell genotype of the zygote.

Genotype– the totality of all the genes of an organism (genetic constitution). From the genotype of the zygote during ontogenesis, many hundreds of different cellular phenotypes arise. Individual cellular phenotypes shape the phenotype of the entire organism. The entire process of life from the formation of the zygote to natural death is controlled by genes. The genotype is constantly exposed to the influence of the external environment, it interacts with the environment, which leads to the formation of all the characteristics and properties of the organism.

Phenotype– all the characteristics of an organism that are formed as a result of the interaction of genotype and environment. (Johansen - 1803) the properties of any organism depend on the genotype and on the environment, therefore the formation of an organism is the result of the interaction of genetic factors and environmental factors.

It was long believed that a zygote contained different chromosomes for different cells, but it is now known that a zygote contains the same genetic information as all cells of a given organism. In specialized cells, genes characteristic of the functions of these cells operate, and all the rest - up to 95% - are blocked. Each embryonic cell has the potential to become any cell in the body, i.e. specialize in any direction - pluripotent cells. Each cell of the body is capable of differentiation in only one way. The direction of specialization is determined by the external environment (the chemical environment of the chromosomes - the cytoplasm). At the earliest stages of embryogenesis, the genotype already interacts with the environment. It is convenient to view the interaction using the example of globin genes. Before and after birth, these genes work differently. In early embryogenesis, the gene responsible for the alpha chain of hemoglobin is turned on (it is active throughout life), and the gene responsible for the synthesis of the beta chain is inactive. But there is a gene responsible for the synthesis of the gamma chain. After birth, the beta chain gene begins to work, and the gamma chain is blocked. These changes are associated with breathing patterns. Fetal hemoglobin easily carries air to the embryo.

The phenotypic manifestation of the genotype, depending on the environment, varies within the normal range of the reaction. From their parents, their offspring receive specific types of chemical reactions to different environmental conditions. The totality of all chemical reactions determines metabolism - metabolism. The metabolic rate varies widely. Each person has his own metabolic characteristics, which are passed on from generation to generation and are subject to Mendelian laws. Differences in metabolism are realized under specific environmental conditions at the level of protein synthesis.

Differential response of primrose plants under different environmental conditions. At normal temperatures of 20-25 degrees and normal pressure - red flowers, at elevated temperatures or pressure - white flowers. The seeds have the same properties.

The Drosophila fly has a gene that causes the wings to close on the back. If flies with mutant genes are hatched at a temperature of 22-25 degrees, the wings are bent. At lower temperatures, the wings are normal and only some have bent wings. The gene determines the synthesis of a thermosensitive protein. Therefore, drying out after emerging from the pupa, deformation of the wings occurs at elevated temperatures.

No traits are inherited. Traits develop based on the interaction of genotype and environment. Only the genotype is inherited, i.e. a complex of genes that determines the norm of the biological reaction of the body, changing the manifestation and severity of symptoms in different environmental conditions. Thus, the body reacts to the properties of the external environment. Sometimes the same gene, depending on the genotype and environmental conditions, manifests a trait differently or changes the completeness of expression.

The degree of manifestation of the phenotype – expressiveness b. Figuratively, it can be compared with the severity of the disease in clinical practice. Expressiveness obeys Gaussian distribution laws (some in small or medium amounts). Variation in expressiveness is based on both genetic and environmental factors. Expressivity is a very important indicator of the phenotypic manifestation of a gene. Its degree is quantified using a statistical indicator.

The genetic trait may not even appear in some cases. If a gene is in the genotype, but it does not appear at all, it is penetrated. (Russian scientist Timofeev-Risovsky 1927). Penetrance– the number of individuals (%) exhibiting a given gene in the phenotype, in relation to the number of individuals in which this trait could manifest itself. Penetrance is characteristic of the expression of many genes. The important principle is “all or nothing” - either it manifests itself or it doesn’t.

Hereditary pancreatitis – 80%

Hip dislocation – 25%

Eye malformations

Retinoblastoma – 80%

Otosclerosis – 40%

Kolotokoma – 10%

Huntington's chorea manifests itself as involuntary jerking of the head. Limbs, gradually progresses and leads to death. It may appear in the early postembryonic period, in adulthood, or not appear at all. Both expressivity and penetrance are maintained by natural selection, i.e. genes that control pathological signs may have different expressivity and penetrance: not all carriers of the gene become ill, and in those who are sick, the degree of manifestation will be different. The manifestation or incomplete manifestation of a trait, as well as its absence, depends on the environment and on the modifying effect of other genes.

1919 Bridges coined the term modifier gene. Theoretically, any gene can interact with other genes, and therefore exhibit a modifying effect, but some genes are more modifiers. They often do not have their own trait, but are able to enhance or weaken the manifestation of a trait controlled by another gene. In the formation of a trait, in addition to the main genes, modifying genes also exert their effect.

Brachydactyly - can be severe or minor. In addition to the main gene, there is also a modifier that enhances the effect.

Coloring of mammals – white, black + modifiers.

The gene can act pleiotropic(plural), i.e. indirectly influence the course of various reactions and the development of many signs. Genes can influence other traits at different stages of ontogenesis. If the gene is turned on in late ontogenesis, then there is an insignificant effect. If in the early stages, the changes are more significant.

Phenylketanuria. Patients have a mutation that turns off the enzyme phenylalanine hydrolase. Therefore, phenylalanine is not converted to tyrosine. As a result, the amount of phenylalanine in the blood increases. If this pathology is detected early (before 1 month) and the child is switched to a different diet, development proceeds normally; if later, the brain size is reduced, mental retardation, does not develop normally, there is no pigmentation, mental abilities are minimal.

Pleiotropy reflects the integration of genes and traits.

A person has a pathological gene that leads to Fanconi syndrome (malformation or absence of the thumb, defect or absence of the radius, underdevelopment of the kidney, brown pigment spots, lack of blood cells).

There is a gene associated with the X chromosome. Immunity to infections and lack of blood cells.

A dominant gene linked to the X chromosome is pilonephritis, labyrinthine hearing loss.

Marfani syndrome – spider fingers, dislocation of the eye lens, heart defects.

Polymerism. If genes are located, each in its own separate locus, but their interaction manifests itself in the same direction - these are polygenes. One gene exhibits the trait slightly. Polygenes complement each other and have a powerful effect - a polygenic system arises - i.e. the system is the result of the action of identically directed genes. Genes are significantly influenced by the main genes, of which more than 50 polygenic systems are known.

Mental retardation is observed in diabetes mellitus.

Height and level of intelligence are determined by polygenic systems

Complementarity– a phenomenon in which there are 2 non-allelic genes. Being in the genotype, they simultaneously lead to the formation of a new trait. If one of the pair is present, it manifests itself.

An example is human blood groups.

Complementarity can be dominant or recessive.

In order for a person to have normal hearing, many genes, both dominant and recessive, must work in concert. If he is homozygous recessive for at least one gene, his hearing will be weakened.

Epistasis– such an interaction of genes when the gene of one allelic pair is masked by the action of another allelic pair. This is due to the fact that enzymes catalyze different cellular processes when several genes act on one metabolic pathway. Their action must be coordinated in time.

Mechanism: if B turns off, it will mask the action of C

B – epistatic gene

C – hypostatic gene

Mccusick:

The relationship between genotype and phenotype is the same as between a person’s character and his reputation: the genotype (and character) is the inner essence of the individual, the phenotype (and reputation) is how he looks or appears to others.”

Genotype- a set of genes of a given organism, which, unlike the concepts of genome and gene pool, characterizes an individual, not a species (another difference between a genotype and a genome is the inclusion in the concept of “genome” of non-coding sequences that are not included in the concept of “genotype”). Together with environmental factors, it determines the phenotype of the organism.

Usually, a genotype is spoken of in the context of a specific gene; in polyploid individuals, it denotes a combination of alleles of a given gene (see homozygote, heterozygote). Most genes appear in the phenotype of an organism, but the phenotype and genotype differ in the following respects:

1. According to the source of information (the genotype is determined by studying the DNA of an individual, the phenotype is recorded by observing the appearance of the organism).

2. The genotype does not always correspond to the same phenotype. Some genes appear in phenotype only under certain conditions. On the other hand, some phenotypes, such as animal fur color, are the result of the interaction of several genes according to the type of complementarity.

Phenotype(from the Greek word phainotype- manifest, discover) - a set of characteristics inherent in an individual at a certain stage of development. The phenotype is formed on the basis of the genotype, mediated by a number of external environmental factors. In diploid organisms, dominant genes appear in the phenotype.

Phenotype is a set of external and internal characteristics of an organism acquired as a result of ontogenesis (individual development).

Despite its seemingly strict definition, the concept of phenotype has some uncertainties. First, most of the molecules and structures encoded by genetic material are not noticeable in the external appearance of the organism, although they are part of the phenotype. For example, this is exactly the case with human blood groups. Therefore, the expanded definition of phenotype should include characteristics that can be detected by technical, medical or diagnostic procedures. A further, more radical extension could include learned behavior or even the organism's influence on the environment and other organisms. For example, according to Richard Dawkins, a beaver's dam, like its incisor teeth, can be considered a phenotype of beaver genes.

Phenotype can be defined as the “carrying out” of genetic information towards environmental factors. To a first approximation, we can talk about two characteristics of the phenotype: a) the number of directions of removal characterizes the number of environmental factors to which the phenotype is sensitive - the dimension of the phenotype; b) the “distance” of removal characterizes the degree of sensitivity of the phenotype to a given environmental factor. Together, these characteristics determine the richness and development of the phenotype. The more multidimensional the phenotype and the more sensitive it is, the further the phenotype is from the genotype, the richer it is. If we compare a virus, a bacterium, an ascaris, a frog and a human, then the richness of the phenotype in this series increases.

Genome- the totality of hereditary material contained in the haploid set of chromosomes of the cells of a given type of organism.

The term “genome” was proposed by Hans Winkler in 1920 to describe the set of genes contained in the haploid set of chromosomes of organisms of the same biological species. The original meaning of this term indicated that the concept of a genome, in contrast to a genotype, is a genetic characteristic of the species as a whole, and not of an individual. With the development of molecular genetics, the meaning of this term has changed. It is known that DNA, which is the carrier of genetic information in most organisms and, therefore, forms the basis of the genome, includes not only genes in the modern sense of the word. Most of the DNA of eukaryotic cells is represented by non-coding (“redundant”) nucleotide sequences that do not contain information about proteins and RNA.

Genetic information in cells is contained not only in the chromosomes of the nucleus, but also in extrachromosomal DNA molecules. In bacteria, such DNA includes plasmids and some mild viruses, in eukaryotic cells it is the DNA of mitochondria, chloroplasts and other cell organelles (See plasmon). The volumes of genetic information contained in germline cells (precursors of germ cells and gametes themselves) and somatic cells in some cases differ significantly. During ontogenesis, somatic cells can lose part of the genetic information of germline cells, amplify groups of sequences and (or) significantly rearrange the original genes.

Consequently, the genome of an organism is understood as the total DNA of the haploid set of chromosomes and each of the extrachromosomal genetic elements contained in an individual cell of the germ line of a multicellular organism. In determining the genome of an individual biological species, it is necessary to take into account, firstly, genetic differences associated with the sex of the organism, since male and female sex chromosomes are different. Secondly, due to the huge number of allelic variants of genes and accompanying sequences that are present in the gene pool of large populations, we can only talk about an average genome, which itself may have significant differences from the genomes of individual individuals. The sizes of the genomes of organisms of different species differ significantly from each other, and there is often no correlation between the level of evolutionary complexity of a biological species and the size of its genome.

Gene pool- a concept from population genetics that describes the totality of all gene variations (alleles) of a certain population. A population has all its alleles for optimal adaptation to its environment. We can also talk about a single gene pool of a species, since genes are exchanged between different populations of the species.

If in the entire population there is only one allele of a certain gene, then the population in relation to the variants of this gene is called monomorphic. When there are several different variants of a gene in a population, it is considered polymorphic.

If the species in question has more than one set of chromosomes, then the total number of different alleles may exceed the number of organisms. However, in most cases the number of alleles is still smaller. With strong inbreeding, monomorphic populations often arise with only one allele of many genes.

One of the indicators of the volume of the gene pool is the effective population size, abbreviated as . A population of people with a diploid set of chromosomes can have a maximum of twice as many alleles of one gene as there are individuals, that is<= 2 * (величины популяции). Исключены при этом половые хромосомы. Аллели всей популяци в идеальном случае распределены по закону Харди-Вайнберга.

A larger gene pool with many different variants of individual genes leads to better adaptation of offspring to a changing environment. The diversity of alleles allows one to adapt to change much more quickly if the corresponding alleles are already present than if they must appear due to mutation. However, in a constant environment, fewer alleles may be more advantageous so that sexual reproduction does not produce too many unfavorable combinations.

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A comment

The concepts of “genotype” and “phenotype” are intimately related to the concepts of “heredity” and “environment”, but are not identical to them. These concepts were introduced by V. Johannsen in 1909. The concept of “genotype” denotes the sum of all the genes of an organism, the hereditary constitution of the organism, the totality of all hereditary inclinations of a given cell or organism, i.e. a set of genes consisting of deoxyribonucleic acid (DNA) molecules and organized into a chromosomal series. The genotype of an organism will be the result of the fusion of two gametes (an egg and the sperm that fertilizes it). The concept of “phenotype” refers to any manifestations of a living organism - its morphological, physiological, psychological and behavioral characteristics. Phenotypes are not inherited, but are formed throughout life; they are the product of an extremely complex interaction between genotype and environment.

Note that there are single traits whose phenotype is completely determined by their genetic mechanisms. Examples of such characteristics are polydactyly (the presence of an extra finger) or a person’s blood type. At the same time, there are very few such traits, and with very rare exceptions, the phenotype of a trait is determined by the joint influence of the genotype and the environment in which the genotype exists.

For any genotype, there is a range of environments in which it can express itself “maximally”; it is impossible to find an environment equally favorable for all genotypes. The point is not in the “richness” of environments, but in their qualitative diversity. There should be a lot of environments so that each genotype has the opportunity to find “the right” environment and realize itself. It is important to note that a monotonous environment, no matter how enriched it may be, will favor the development of only certain, and not all genotypes.

Reaction norm concept and development

The population approach to assessing the heritability of behavioral traits does not allow us to describe the processes of interaction between genotype and environment in individual development. When, as a result of psychogenetic studies conducted, say, on twins or adopted children, a trait is classified as heritable, this does not mean that it is hereditarily determined in the generally accepted sense of the word.

Psychogenetic research is carried out mainly at the population level. When population geneticists draw a conclusion about the heritability of a trait based on correlated behavior in relatives, this does not mean that the individual development of this behavior is due solely to genetic reasons.

High heritability only indicates that the diversity of individuals in a population is largely associated with genotypic differences between them. This means that the percentage of individuals possessing a given trait in a population of offspring can be predicted based on knowledge about the parent population. However, the value of the heritability indicator does not say anything about the sequence of events in the individual development of the trait and what final phenotype will be the result of the development of a particular individual. In this sense, a trait with a high heritability estimate is not a determined genotype, although such interpretations are often found even in the publications of specialists. These are completely different things - to divide the sources of variation in a population into genetic and environmental ones or to look for genetic and environmental reasons that underlie the ontogenetic formation of specific phenotypes.

Even with 100% heritability, as it is understood in behavioral genetics, there is the possibility of environmental influence on the formation of a trait in individual development. This approach corresponds to genetic ideas about the norm of reaction. Let us remember that it is not the trait that is inherited, but the reaction norm.

Special attention should be paid to the reaction norm in this section. In many genetics textbooks, in school biology courses and other books, the reaction norm is often understood as the limits that the genotype places on the formation of the phenotype. This understanding of the reaction norm, in our opinion, is less productive than the one we adhere to in the course of presenting the material. The reaction norm is the specific nature of the genotype’s reaction to environmental changes. The introduction of the concept of limit into the definition of a reaction norm is quite understandable, since under ordinary standard conditions of development, genotypes indeed limit the possibilities for the development of phenotypes. For example, people with good genetic inclinations for the development of intelligence, all other things being equal, will always be ahead of people with poor inclinations. It is believed that the environment can shift the final outcome of development, but within a range that is genetically determined. But, in reality, this is a false premise, since we can never be sure that a trait has reached the maximum development possible for a given genotype.

The pattern of phenotypic manifestations of a genotype cannot be tested for all possible environments because they are uncertain. In relation to humans, we not only do not have the opportunity to arbitrarily control the parameters of the environment in which development occurs, but often, when analyzing environmental influences on a trait, we even find it difficult to select those parameters about which information needs to be obtained, especially when it comes to behavioral characteristics.

Modern developmental psychobiology provides more and more data on the significant capabilities of the environment, in the frequency of early experiences, including embryonic ones, to influence the activity of genes and the structural and functional formation of the nervous system. Thus, if in a traditional environment the illusion is created that there are limits to the formation of a phenotype, then we cannot be sure that development, during which the genotype will be subjected to unusual, unconventional influences, will not lead to the emergence of such behavioral features that in ordinary conditions under this genotype would be impossible. Thus, it is more correct to think that the limits of the phenotype are unknowable.

Many people follow with interest publications about unconventional methods of raising babies, and some parents try them on their children. Someone is trying to raise a musician, starting from the prenatal period, when the mother carrying the child, with the help of simple devices, ensures that her fetus listens to musical works or sings lullabies to the unborn child. Some give birth in water and then swim with the newborn in a bathtub or pool. Some people are interested in dynamic gymnastics and conditioning. Increasingly, in maternity hospitals, the baby is not separated from the mother in the first minutes of life, as was traditionally done before, but even before the umbilical cord is cut, they are placed on her stomach, ensuring such natural contact between the mother and the newborn.

All these “experiments” are nothing more than the influence of non-traditional (for a given period of development of society) early experience on the fetus and newborn, and these influences are not meaningless, since the intensively developing nervous system, on which, ultimately, will depend our behavior and all higher mental functions are very susceptible to influence precisely in the early period of ontogenesis. What is known today about the influence of early experience, that is, the environment, on the development of the nervous system and can this environment directly influence the functioning of the genetic apparatus? In other words, this is a question of what knowledge we have about the process of interaction between genotype and environment in individual development.

How can environment interact with genotype during development?

It is clear that the result of development - the phenotype - depends on the joint action of genes and the environment. Genes and traits are linked through a complex network of developmental pathways. All individual differences that differential psychologists and psychogeneticists are concerned with are the result of the developmental circumstances of specific individuals in specific environments. Often individuals brought up in apparently different environments have much in common. Conversely, siblings raised in the same family, seemingly under similar circumstances, due to subtle differences in the conditions of upbringing and development, will actually experience very different influences from both the physical and social environment.

Thus, the process of interaction with the environment is complex and ambiguous. Note also that psychologists and other researchers often use the term “interaction” in a statistical sense when examining the interaction of individual factors in the production of any measurable effect. We emphasize that the statistical interaction of factors and the interaction of genes and environment in individual development are completely different things. They should not be confused.

For us, the formulation is quite familiar, which states that the manifestation of a phenotype is the result of the interaction of the genotype with the environment during development. However, if you think about this statement, it does not seem so obvious. After all, interaction presupposes that its participants come into contact and come into contact. In fact, our genotype, that is, the genetic apparatus, is hidden deep inside the cell and is separated from the external environment not only by the integument of the body, but also by the cellular and nuclear membranes. How can the external environment interact with genetic structures?

It is clear that genes and the surrounding world are not in direct contact. The organism as a whole interacts with the external environment; genes interact with various biochemical substances inside the cell. But various cellular substances can be influenced by the outside world. Let's consider what is known about these processes today's science. To do this, we will again have to turn to molecular genetics and consider in more detail how genes function, since in the previous presentation we only stated that the main function of a gene is to encode the information necessary for the synthesis of a specific protein.

Accidents of development

The variability of developmental phenomena depends on many reasons. Heredity tends to reduce developmental variability, whereas conditions not associated with heredity tend to increase it. Some developmental researchers identify four types of random factors that influence developmental variability:

• accidents in the selection of parental pairs, the genes of which make up the genotype of the individual;
• randomness of epigenetic (that is, external to the genotype) processes within individual ontogenesis;
• the randomness of the maternal environment in which the individual develops;
• the randomness of the non-maternal environment in which the individual develops.

Although these are random events, they all have an element of heredity. The genotype is inherited from the parents, and the offspring and parents have common genes that influence the course of individual development. Epigenetic processes within the body represent the influence of other cells or their products on the activity of the genotype of a given cell. Since all cells in the body have the same genotype, it is natural that epigenetic influences are associated with heredity. However, epigenetic processes are stochastic, open to the influence of environmental factors of the organism and, therefore, to any historical accidents.

The maternal environment of mammals is a very important element of the external environment. Mothers provide the intrauterine and postnatal (baby care and education) environment for the child. It is clear that these conditions are influenced by the mother's genotype. Partially, the mother's genes are shared with the offspring, so the maternal environment can be inherited. The maternal environment is also sensitive to historical contingencies.

Nonmaternal environmental effects also influence developmental variability. This includes factors that are chosen by the individual himself or shaped by the people around him, including relatives with whom he shares genes. Therefore, these environmental effects, to some extent, are also influenced not only by random environmental events, but also by genes, and are also inherited (genotype-environmental covariation).

Thus, in accordance with the above classification, in all the described elements of the environment external to a given individual, there are mechanisms for inheritance, both genetic and non-genetic (various traditions, etc.).

Naturally, non-heritable factors also influence development. These are those features of the environment that are not associated with changes caused by the developing individual himself or his related environment. They can be either random or natural. Regular changes include cyclical changes (change of day and night, change of seasons, etc.), widespread influences (gravity) or predictable factors (temperature, pressure). Non-heritable factors are also present in the maternal and other social environment (quality of maternal nutrition, maternal stress level, number and gender of siblings, etc.). Randomly or systematically changing environmental events contribute to variability in development.

All events external to genes that take place during the process of ontogenesis, together with genetic factors, create the background against which development takes place. Due to the impact of a huge variety of regular and random events in ontogenesis, developing systems can organize and reorganize. Genes make development possible, but other components that influence the development of the system are no less important participants in the development process.

At the beginning of the presentation, defining the concept of phenotype, we emphasized that the phenotype is the result of the interaction of the genotype and the environment, however, in the light of what has been said about the process of individual development, we must make some clarification in this formulation and, along with environmental factors, mention accidents of development that cannot be reduced to purely environmental influences. If we tried to graphically depict the dependence of the phenotype on various factors, then we would need at least a four-dimensional space in which, in addition to the axes for genotype and environment, there would also have to be an axis for the accidents of development.

Endophenotype as an intermediate level between genotype and phenotype

The wide range of CIs of different abilities makes it necessary to address the intermediate level between genotype and phenotype. If the genotype is the sum of all the genes of an organism, then the phenotype is any manifestations of a living organism, “the product of the implementation of a given genotype in a given environment.” There is no direct correspondence between the gene (genotype) and behavior (phenotype), but only a repeatedly mediated connection. Phenotypically identical traits measured using the same methodology may have different psychological structures depending on the age and individual characteristics of the individual and, accordingly, may be associated with different genes. The presence, absence, and degree of expression of one phenotypic trait are determined by many genes, the result of which depends not only on the available gene variants, but also on many other factors. “The direct biochemical expression of a gene and its influence on psychological characteristics are separated by a “mountain range” of intermediate biomolecular events.” Therefore, one of the ways to facilitate tracing the path from genes to behavior is to find endophenotypes—intermediate links that mediate the influence of the genotype on phenotypic variables.

The concept of endophenotype, introduced by I. Gottesman in 1972 when studying mental disorders, has become widespread in the analysis of psychological and psychophysiological characteristics.

A trait or indicator can be recognized as an endophenotype of cognitive abilities if it meets the following criteria:

1. it is stable and reliably determined;
2. its genetic condition was revealed;
3. it correlates with the cognitive ability being studied (phenotypic correlation);
4. the relationship between it and cognitive ability is partly inferred from common genetic sources (genetic correlation). And if the task is to trace the biological path from genes to cognitive ability, then it is important to fulfill one more criterion;
5. the presence of a theoretically meaningful (including causal) relationship between the indicator and cognitive ability.

It is customary to consider private cognitive characteristics or individual characteristics of the functioning of the brain, its anatomy and physiology as endophenotypes of intelligence.

Among the private cognitive characteristics, the reaction time of choice is used. It is known that individual differences in choice reaction time explain about 20% of the variance in intelligence scores. It was found that the associations between choice reaction time and verbal and non-verbal intelligence scores were explained by genetic factors: 22 and 10% of common genes were found, respectively. It is assumed that among the common genes there are those responsible for the myelination of CNS axons (as is known, an axon covered with a myelin sheath conducts a nerve impulse faster). Particular cognitive characteristics considered as endophenotypes of intelligence include working memory. However, we note that neither choice reaction time, nor working memory, nor other psychological parameters important for understanding the nature of intellectual differences, still do not reveal the path from genotype to intelligence through the structure and functioning of the brain, since they are not direct indicators of brain function. In addition, when using these indicators, we again encounter the above-mentioned high sensitivity of the CI to changes in experimental conditions.

Parameters of brain functioning at different levels of physiology, morphology and biochemistry of the brain, including structural proteins, enzymes, hormones, metabolites, etc. are also considered possible endophenotypes. The EEG, the speed of nerve impulses, the degree of myelination of nerve fibers, etc. are examined. It has been shown that peripheral nerve conduction velocity (PNCV) and brain size correlate with intelligence. Amplitude-time and topographic characteristics of evoked potentials were studied as intermediate phenotypes of intelligence. However, theoretical justifications for the connections of these characteristics with intelligence, as a rule, do not reveal the specifics of intellectual abilities. Thus, brain size is correlated with the thickness of the myelin sheath, which may be less or better at protecting cells from the influence of neighboring neurons, which is said to influence intelligence. SPNP determines the quantitative characteristics of protein transmission, and its limitation leads to a limitation in the speed of information processing, which leads to a decrease in intelligence indicators.

A connection has been established between the general intelligence factor (g factor) and the amount of gray matter. Another possible endophenotype of cognitive abilities is the specific arrangement of brain structures. It is revealed that the CI of the structural characteristics of the brain is very high, especially in the frontal, associative and traditional speech zones (Wernicke and Broca). Thus, in the area of ​​the median frontal structures, we can reliably speak of a CI of the order of 0.90–0.95.

However, endophenotypes that directly reflect the morphofunctional characteristics of the brain do not take into account the ability to plan activities, the strategies used and other features that significantly affect the success and speed of problem solving, i.e. do not take into account the psychological organization of the phenotype under study (cognitive abilities). There is an indirect connection between endophenotypes of this kind and intelligence: endophenotypes reflect a level of analysis that is far from intelligence and therefore do not provide a holistic picture of the path to the formation of intellectual functions.

E. De Geus and co-authors consider it very productive to use neurophysiological characteristics and the results of direct measurements of brain structures and their functioning using EEG, MRI, etc. as endophenotypes (in addition to special cognitive abilities).

However, the use of neurophysiological indicators in studies on behavioral genetics leads to the need to adapt neuroscience methods to the requirements of psychogenetics. The problem is that, as R. Plomin and S. Kosslin write, neuroscience is primarily interested in general patterns, as a result of which data are usually averaged and only average values ​​are analyzed. Psychogenetics, on the contrary, is interested in the scatter of individual indicators, which in a number of neuroscience methods reflects not only individual characteristics, but also the insufficient accuracy of the equipment. This creates significant difficulties in obtaining reliable data. In addition, the technical complexity of these methods does not allow the study of large enough samples necessary for psychogenetic analysis.

conclusions

1. Developmental research in psychogenetics is conducted at the population level; the resulting quantitative relationships between the genetic and environmental components of variability are not applicable to the development of a specific phenotype. It must be remembered that the mutual influences of genotype and environment in individual development are inseparable.
2. The formation of a phenotype in development occurs through continuous interaction between the genotype and the environment. Environmental factors (physical, social) can influence the genotype through factors of the internal environment of the body (various biochemical substances inside the cell).
3. The main mechanism of interaction between genotype and environment at the cellular level is the regulation of gene expression, manifested in different activity of specific protein synthesis. Most of the regulatory processes occur at the transcription level, that is, they concern the processes of reading genetic information necessary for protein synthesis.
4. Among all the organs of the body, the brain ranks first in the number of active genes. According to some estimates, almost every second gene in the human genome is associated with the functions of the nervous system.
5. Early experience has significant opportunities to influence the functioning of the genetic apparatus. A special role here belongs to the so-called early genes, which are capable of rapid but transient expression in response to signals from the external environment. Apparently, early genes play a significant role in learning processes. Significant possibilities for regulating gene expression are also associated with the action of various hormones.
6. The development of the nervous system and, ultimately, behavior is a dynamic, hierarchically organized systemic process in which genetic and environmental factors are equally important. An important role is also played by various accidents of development, which cannot be reduced to purely environmental ones.
7. Development is an epigenetic process that results in significant interindividual variability, even in isogenic organisms. The basic principle of the morphogenesis of the nervous system is the occurrence of maximum redundancy of cellular elements and their connections in the early stages of development, followed by the elimination of functionally unstable elements in the process of reciprocal interaction between all levels of the developing system, including interactions within the cell, between cells and tissues, between the organism and the environment.
8. The process of phenotype formation in development is of a continuous dialectical and historical nature. At any stage of ontogenesis, the nature of the body’s response to environmental influences is determined both by the genotype and the history of all developmental circumstances.

Hello, dear blog readers Biology tutor via Skype .

This is what “parsley” looks like, to say the least. Once again I am faced with the fact that the fundamental concepts of genetics in textbooks are presented in such a way that it can be difficult to understand them.

I was tempted to call this article that way at first "Phenotype and genotype." It is clear that the phenotype is secondary to the genotype. But if students can most often interpret the term “genotype” correctly, then as it turns out, there is no clear idea regarding the concept of “phenotype”.

How can it be “clear” if the definitions of phenotype in educational literature are so vague.

"Phenotype- the totality of all external characteristics of an organism, determined by genotype and environmental conditions.” Or “Phenotype is the totality of all external and internal characteristics and properties of an organism, depending on the genotype and environmental conditions.”

And if there really are both “external” and “internal”, and this is actually the case, then what is the difference between a phenotype and a genotype?

Still, you have to start not from the “tail”, but from the “head”. I am sure that a couple of minutes will pass and you, having somewhat clarified for yourself what the “genotype of an organism” is, will be able to get a clearer idea of ​​the “phenotype”.

We often use the terms “trait” and “gene” as synonyms.

They say that “a genotype is the totality of all the characteristics of an organism.” And here it is important to understand the most important thing - it is precisely in the determination of the genotype that such a definition introduces additional confusion. Yes, indeed, information about any trait is encoded in any gene (or set of genes) of the organism.

But there are a lot of genes, the entire genotype of an organism is huge, and during the life of a given individual or individual cell, only a small part of the genotype is realized (that is, serves to form any specific characteristics).

Therefore, it would be correct to remember that "genotype- the totality of all genes organism." And which of these genes are realized during the life of the organism in its phenotype, that is, will serve the formation of any signs- this depends both on the interaction of many of these genes and on specific environmental conditions.

Thus, if we correctly understand what a genotype is, then there is no loophole for confusion in terms of what is a “genotype” and what is a “phenotype”.

It is clear that “a phenotype is the totality of all genes realized during the life of an organism that contributed to the formation of specific characteristics of a given organism under certain environmental conditions.”

Therefore, throughout the life of an organism, under the influence of changing environmental conditions, the phenotype can change, although it is based on the same unchanged genotype. And within what limits can the phenotype change?

Norm of reaction

These boundaries for the phenotype are clearly delineated by the genotype and are called “reaction norms.” After all, nothing can appear in the phenotype that was not already “recorded” earlier in the genotype.

To better understand what is meant by the concept of “reaction norm,” let us look at specific examples of the possible manifestation of a “broad” or “narrow” reaction norm.

The weight (mass) of the cow and the milk yield of the cow, which trait has a wider and which has a narrower reaction rate?

It is clear that the weight of an adult cow of a certain breed, no matter how well it is fed, cannot exceed, for example, 900 kg, and if it is poorly maintained, it cannot be less than 600 kg.

What about milk yield? With optimal housing and feeding, milk yield can vary from some maximum possible value for a given breed; it can drop to 0, under unfavorable housing conditions. This means that the mass of a cow has a rather narrow reaction rate, and the milk yield is very wide.

Example with potatoes. It is obvious to anyone that the “tops” have a rather narrow reaction rate, and the mass of tubers has a very wide one.

I think everything has settled down now. The genotype is the set of all the genes of an organism, this is its entire potential of what it can be capable of in life. And the phenotype is only a manifestation of a small part of this potential, the implementation of only part of the organism’s genes into a number of specific characteristics during its life.

A clear example of the transformation of part of its genotype into a phenotype during the life of an organism are identical twins. Having absolutely the same genotype, in the first years of life they are almost indistinguishable from each other phenotypically. But as they grow up, having at first minor differences in behavior, in some attachments, giving preference to one or another type of activity, these twins become quite distinguishable phenotypically: in facial expression, body structure.

At the end of this note, I would like to draw your attention to something else. The word genotype for students of the basics of genetics has two meanings. Above we examined the meaning of “genotype” in its broad sense.

But to understand the laws of genetics, when solving genetic problems, the word genotype means only a combination of some specific individual alleles of one (monohybrid crossing) or two (dihybrid crossing) pairs of certain genes that control the manifestation of a specific one or two traits.

That is, our phenotype is somehow truncated, we say “the phenotype of an organism,” but we ourselves have studied the mechanism of inheritance of only one or two of its characteristics. In a broad sense, the term “phenotype” refers to any morphological, biochemical, physiological and behavioral characteristics of organisms.

P.S. In connection with the characteristics of the concepts “genotype” and “phenotype,” it would be appropriate here to examine the question of hereditary and non-hereditary forms of variability in organisms. Well, okay, that’s exactly what we’ll talk about in.

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