The genotype is the totality of all the genes of an organism, which are its hereditary basis.

Phenotype - the totality of all the 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.

Each species has its own unique phenotype. It is formed in accordance with the hereditary information embedded in the genes. However, depending on changes in the external environment, the state of signs varies from organism to organism, resulting in individual differences - variability.

Based on the variability of organisms, a genetic diversity of forms appears. There are modification variability, or phenotypic, and genetic, or mutational.

Modification variability does not cause changes in the genotype, it is associated with the reaction of a given, one and the same genotype to a change in the external environment: under optimal conditions, the maximum possibilities inherent in a given genotype are revealed. Modification variability is manifested in quantitative and qualitative deviations from the original norm, which are not inherited, but are only adaptive in nature, for example, increased pigmentation of human skin under the influence of ultraviolet rays or development of the muscular system under the influence of physical exercises, etc.

The degree of variation of a trait in an organism, that is, the limits of modification variability, is called the reaction norm. Thus, the phenotype is formed as a result of the interaction of the genotype and environmental factors. Phenotypic traits are not transmitted from parents to offspring, only the norm of reaction is inherited, that is, the nature of the response to changes in environmental conditions.

Genetic variability is combinative and mutational.

Combination variability arises as a result of the exchange of homologous regions of homologous chromosomes during meiosis, which leads to the formation of new gene associations in the genotype. Arises as a result of three processes: 1) independent divergence of chromosomes in the process of meiosis; 2) their accidental connection during fertilization; 3) exchange of sections of homologous chromosomes or conjugation. .

Mutational variability (mutations). Mutations are called spasmodic and stable changes in the units of heredity - genes, entailing changes in hereditary traits. They necessarily cause changes in the genotype that are inherited by offspring and are not associated with crossing and recombination of genes.

There are chromosomal and gene mutations. Chromosomal mutations are associated with changes in the structure of chromosomes. This may be a change in the number of chromosomes that is a multiple or not a multiple of the haploid set (in plants - polyploidy, in humans - heteroploidy). An example of heteroploidy in humans can be Down syndrome (one extra chromosome and 47 chromosomes in the karyotype), Shereshevsky-Turner syndrome (one X chromosome is missing, 45). Such deviations in the human karyotype are accompanied by a health disorder, a violation of the psyche and physique, a decrease in vitality, etc.

Gene mutations - affect the structure of the gene itself and entail a change in the properties of the body (hemophilia, color blindness, albinism, etc.). Gene mutations occur in both somatic and germ cells.

Mutations that occur in germ cells are inherited. They are called generative mutations. Changes in somatic cells cause somatic mutations that spread to that part of the body that develops from the changed cell. For species that reproduce sexually, they are not essential, for vegetative reproduction of plants they are important.

Organisms in the phenotype manifest dominant genes.

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

Despite a seemingly rigorous definition, the concept of the phenotype has some uncertainties. First, most of the molecules and structures carried by the genetic material are not visible in the external appearance of the organism, although they are part of the phenotype. For example, this is the case with human blood types. Therefore, an extended definition of the phenotype should include characteristics that can be detected by technical, medical or diagnostic procedures. A further, more radical extension may include learned behavior or even the influence of an organism on its environment and other organisms. For example, according to Richard Dawkins, the dam of beavers, as well as their incisors, can be considered a beaver gene phenotype.

The phenotype can be defined as the "removal" of genetic information towards environmental factors. In the first approximation, we can talk about two characteristics of the phenotype: a) the number of outflow directions characterizes the number of environmental factors to which the phenotype is sensitive - the dimensionality of the phenotype; b) "range" 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 grows.

Genetic factors influencing the formation of the phenotype[ | ]

The history of any phenotype preserved by long-term selection is a chain of successive tests of its carriers for the ability to reproduce themselves under conditions of continuous change in the variation space of their genomes. ...
... Changes in the genotype do not determine evolution and its direction. On the contrary, the evolution of an organism determines the change in its genotype.

- Shmalgauzen I.I. The organism as a whole in individual and historical development. Selected works .. - M .: Nauka, 1982.

These factors include the interaction of genes from one (dominance, recessiveness, incomplete dominance, dominance) and different (dominant and recessive epistasis, hypostasis, complementarity) alleles, multiple alleles, pleiotropic effect of the gene, gene dose.

History reference[ | ]

The term phenotype was proposed by the Danish scientist Wilhelm Johansen in 1909, along with the concept of genotype, in order to distinguish the heredity of an organism from what results from its implementation. The idea of ​​the difference between the carriers of heredity and the result of their action can be traced already in the works of Gregor Mendel (1865) and August Weismann. The latter distinguished (in multicellular organisms) reproductive and somatic cells.

Phenotypic variance[ | ]

Phenotypic variance (determined by genotypic variance) is a basic prerequisite for natural selection and evolution. The organism as a whole leaves (or does not leave) offspring, so natural selection affects the genetic structure of the population indirectly through the contributions of phenotypes. Without different phenotypes, there is no evolution. At the same time, recessive alleles are not always reflected in the traits of the phenotype, but are preserved and can be passed on to offspring.

Phenotype and ontogeny[ | ]

The factors that determine phenotypic diversity, the genetic program (genotype), environmental conditions and the frequency of random changes (mutations) are summarized in the following relationship:

genotype + environment + random changes → phenotype

The ability of a genotype to form in ontogenesis, depending on environmental conditions, different phenotypes is called reaction norm. It characterizes the share of participation of the environment in the implementation of the feature. The wider the reaction norm, the greater the influence of the environment and the less the influence of the genotype in ontogeny. Usually, the more diverse the habitat conditions of a species, the wider its reaction rate.

Examples [ | ]

Sometimes phenotypes in different conditions are very different from each other. So, the pines in the forest are tall and slender, and in the open space - spreading. The shape of the leaves of the water ranunculus depends on whether the leaf is in the water or in the air. In humans, all clinically detectable traits - height, body weight, eye color, hair shape, blood type, etc. - are phenotypic.

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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 W. Johannsen in 1909. The concept of "genotype" refers to the sum of all genes of an organism, the hereditary constitution of an 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 chromosome row. The genotype of an organism will be the result of the fusion of two gametes (the egg and the sperm that fertilizes it). The concept of "phenotype" denotes any manifestations of a living organism - its morphological, physiological, psychological and behavioral features. Phenotypes are not inherited, but are formed during life; they are the product of an extremely complex interaction between genotype and environment.

Note that there are single signs, the phenotype of which is completely determined by their genetic mechanisms. Examples of such signs 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 combined 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 manifest itself "maximally"; An environment that is equally favorable for all genotypes cannot be found. The point is not the "enrichment" of the environments, but their qualitative diversity. There should be a lot of environments, so that each genotype would have the opportunity to find a "sʙᴏ" environment and be realized. It is important to note that a uniform environment, no matter how enriched it may be, will favor the development of only certain, and not all, genotypes.

The concept of reaction rate and development

The population approach to assessing the heritability of behavioral characteristics does not allow one to describe the processes of interaction between the genotype and the environment in individual development. When, as a result of psychogenetic studies conducted, say, on twins or adopted children, a trait is classified as inherited, 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, on the basis of correlated behavior in relatives, population geneticists conclude that a trait is heritable, this does not mean that the individual development of this behavior is due solely to genetic causes.

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 with a given trait in a population of offspring can be predicted based on knowledge of the parent population. However, the value of the heritability index does not say anything about the sequence of events in the individual development of a trait and about what final phenotype will be the result of the development of a particular individual. In this sense, a trait with a high heritability score is not a deterministic genotype, although such interpretations are often found even in specialist publications. These are completely different things - to divide the sources of variability in a population into genetic and environmental, or to look for genetic and environmental causes underlying the ontogenetic formation of specific phenotypes.

Even with 100% heritability, as understood in behavioral genetics, there is room for environmental influences on trait formation in individual development. This approach corresponds to genetic ideas about the norm of the reaction. Recall that it is not the trait that is inherited, but the norm of the reaction.

The rate of reaction in this section should be discussed separately. In many textbooks of genetics, in the school biology course and other books, the reaction rate is often understood as the limits that the genotype puts on the formation of the phenotype. Such an 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 rate is the specific nature of the reaction of the genotype to changes in the environment. The introduction of the concept of a limit into the definition of the reaction norm is quite understandable, since under normal standard conditions of development, indeed, genotypes limit the possibilities for the development of phenotypes. For example, people with good genetic inclinations for the development of intelligence, other things being equal, will always outperform people with poor inclinations. It is believed that the environment can shift the final result 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 the trait has reached the maximum development possible for a given genotype.

The nature of the phenotypic manifestations of a genotype cannot be tested for all possible environments, as they are indeterminate. In relation to a person, we not only do not have the opportunity to arbitrarily control the parameters of the environment in which development takes place, but often, when analyzing environmental influences on a trait, we find it difficult even in choosing those parameters that we need to obtain information about, especially when it comes to behavioral characteristics.

Modern developmental psychobiology provides more and more data on the significant possibilities of the environment, in the frequency of early experience, including embryonic experience, to influence gene activity 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 the phenotype, then we cannot be sure that development, during which the genotype will be exposed to unusual, non-traditional influences, will not lead to the emergence of such behavioral features that in ordinary conditions for this genotype would be impossible. Thus, it is more correct to consider that the limits of the phenotype are unknowable.

Many people follow with interest publications about non-traditional 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 a mother carrying a child, with the help of simple devices, provides her fetus with listening to music or sings lullabies to an unborn child herself. Some give birth in the water and then swim with the newborn in the tub or pool. Someone is fond of dynamic gymnastics and hardening. Increasingly, in maternity hospitals, the baby is not weaned from the mother in the first minutes of life, as was traditionally done before, and even before cutting the umbilical cord, they are placed on her stomach, providing such a natural contact between the mother and the newborn.

All these "experiments" are nothing more than the impact of non-traditional (for a given period of development of society) early experience on the fetus and newborn, and these effects are not without meaning, since the intensively developing nervous system, on which, ultimately, will depend our behavior and all higher mental functions are very susceptible to influences 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 affect the work of the genetic apparatus? In other words, it is a question of what knowledge about the process of interaction between the genotype and the environment in individual development we have.

How can the environment interact with the genotype during development?

It is clear that the result of development - the phenotype - depends on the combined action of genes and the environment. Genes and traits are linked in a complex web of developmental pathways. All individual differences that differential psychologists and psychogenetics deal with are the result of the developmental circumstances of particular individuals in particular environments. Often individuals brought up in apparently different environments have much in common. And vice versa, siblings brought up 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 of 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 producing some measurable effect. We emphasize that the statistical interaction of factors and the interaction of genes and the environment in individual development are completely different things. They should not be confused.

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

It is clear that genes and the surrounding world do not directly touch. 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 us consider what is known about these processes by 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, while non-hereditary conditions tend to increase it. Some developmental researchers identify four types of random factors that affect developmental variability:

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

Although these are random events, however, they all have an element of heredity. The genotype is inherited from the parents, and the offspring with the parents have common genes that affect the course of individual development. Epigenetic processes within an organism are the influences of other cells or their products on the activity of a given cell's genotype. Since all cells in an organism share the same genotype, it is natural that epigenetic influences are related to 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 (infant care and upbringing) environment for the child. It is clear that these conditions are affected by the genotype of the mother. Partially, the mother's genes are common with the offspring, so the maternal environment can be inherited. The mother environment is also sensitive to historical contingencies.

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

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

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

All events external to genes that take place in the process of ontogenesis, together with genetic factors, create the background against which development proceeds. Due to the impact of a huge variety of regular and random events in ontogeny, developing systems can organize and reorganize. Genes make development possible, but other components that influence the development of the system are equally important participants in the development process.

At the beginning of the presentation, defining the concept of the 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 the genotype and the environment, there would also have to be an axis for developmental chances.

Endophenotype as an intermediate level between genotype and phenotype

A large spread of CI of different abilities makes it necessary to address the intermediate level between the genotype and phenotype. If the genotype is the sum of all the genes of an organism, then the phenotype is any manifestation of a living organism, "the product of the realization of a given genotype in a given environment." There is no direct correspondence between a gene (genotype) and behavior (phenotype), but only a repeatedly mediated connection. Phenotypically the same traits, measured by the same method, may have a different psychological structure 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 effect on psychological characteristics are separated by a 'mountain' of intermediate biomolecular events." Therefore, one of the ways to facilitate tracing the path from genes to behavior was 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 in the study of 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 satisfies the following criteria:

1. it is stable and reliably determined;
2. its genetic conditionality 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 shared 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.

As endophenotypes of intelligence, it is customary to consider particular cognitive characteristics or individual features of the functioning of the brain, its anatomy and physiology.

Of the particular cognitive characteristics, the reaction time of choice is used. It is known that individual differences in choice reaction time explain about 20% of the dispersion of intelligence values. It was found that the links between choice reaction time and values ​​of verbal and non-verbal intelligence are 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, a myelin-coated axon conducts a nerve impulse faster). Particular cognitive characteristics considered as endophenotypes of intelligence include working memory. However, we note that neither the reaction time of choice, nor working memory, nor other psychological parameters important for understanding the nature of intellectual differences still reveal the path from the genotype to intelligence through the structure and functioning of the brain, since they are not direct indicators of brain functioning. In addition, when using these indicators, we again encounter the high sensitivity of the QN to changes in the experimental conditions mentioned above.

Possible endophenotypes are also considered parameters of brain functioning at different levels of physiology, morphology, and biochemistry of the brain, including structural proteins, enzymes, hormones, metabolites, etc. The EEG, the speed of nerve impulses, the degree of myelination of nerve fibers, etc. are being studied. It has been shown that intelligence correlates with peripheral nerve conduction velocity (PNR), brain size. Amplitude-time and topographic characteristics of evoked potentials were studied as intermediate phenotypes of intelligence. However, theoretical substantiations of the links between these characteristics and intelligence, as a rule, do not reveal the specifics of intellectual abilities. Thus, the size of the brain correlates with the thickness of the myelin sheath, which can better or worse protect cells from the influence of neighboring neurons, which is said to affect 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 was 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 areas (Wernicke and Broca). Thus, in the region of the median frontal structures, one can reliably speak of a CV of the order of 0.90–0.95.

However, endophenotypes that directly reflect the morphological and functional 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 solving problems, i.e. do not take into account the psychological organization of the studied phenotype (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 view of the path of formation of intellectual functions.

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

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

conclusions

1. Developmental research in psychogenetics is conducted at the population level; the resulting quantitative ratios of genetic and environmental components of variability are not applicable to the development of a particular phenotype. It must be remembered that the mutual influences of the genotype and the environment in individual development are inseparable.
2. The formation of the phenotype in development occurs with the continuous interaction of the genotype and the environment. Environmental factors (physical, social) can influence the genotype through factors of the body's internal environment (various biochemical substances inside the cell).
3. The main mechanism of interaction between the genotype and the environment at the cell level is the regulation of gene expression, which manifests itself in different activity of specific protein synthesis. Most of the regulation processes occur at the level of transcription, that is, it concerns the processes of reading genetic information necessary for protein synthesis.
4. Among all organs of the body, the brain ranks first in terms of the number of active genes. According to some estimates, almost every second gene in the human genome is associated with the provision of the functions of the nervous system.
5. Early experience has significant opportunities to influence the work 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 opportunities for the regulation of 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 leading to the formation of significant interindividual variability even in isogenic organisms. The main principle of the morphogenesis of the nervous system is the emergence of a maximum redundancy of cellular elements and their connections at 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 formation of the phenotype in development has a continuous dialectical and historical character. At any stage of ontogeny, the nature of the organism's reaction to the impact of the environment is determined both by the genotype and the history of all developmental circumstances.

Genetics has repeatedly amazed us with its achievements in the study of the human genome and other living organisms. The simplest manipulations and calculations cannot do without generally accepted concepts and signs, which this science is not deprived of either.

What are genotypes?

The term refers to the totality of genes of one organism, which are stored in the chromosomes of each of its cells. The concept of genotype should be distinguished from the genome, since both words have a different lexical meaning. Thus, the genome represents absolutely all the genes of a given species (human genome, monkey genome, rabbit genome).

How is the human genotype formed?

What is a genotype in biology? Initially, it was assumed that the set of genes of each cell of the body is different. Such an idea has been refuted since the moment scientists discovered the mechanism for the formation of a zygote from two gametes: male and female. Since any living organism is formed from a zygote through numerous divisions, it is easy to guess that all subsequent cells will have exactly the same set of genes.

However, the genotype of the parents should be distinguished from that of the child. The fetus in the womb has half of the set of genes from mom and dad, so children, although they look like their parents, are not 100% copies of them at the same time.

What is genotype and phenotype? What is their difference?

The phenotype is the totality of all external and internal features of an organism. Examples are hair color, freckles, height, blood type, hemoglobin count, enzyme synthesis or absence.

However, the phenotype is not something definite and permanent. If you watch hares, then the color of their coat changes depending on the season: in summer they are gray, and in winter they are white.

It is important to understand that the set of genes is always constant, and the phenotype can vary. If we take into account the vital activity of each individual cell of the body, any of them carries exactly the same genotype. However, insulin is synthesized in one, keratin in the other, and actin in the third. Each is not similar to each other in shape and size, functions. This is called phenotypic expression. This is what genotypes are and how they differ from the phenotype.

This phenomenon is explained by the fact that during the differentiation of embryonic cells, some genes are switched on, while others are in a “sleep mode”. The latter either remain inactive all their lives or are reused by the cell in stressful situations.

Examples of recording genotypes

In practice, the study is carried out using conditional encoding of genes. For example, the gene for brown eyes is written with a capital letter "A", and the manifestation of blue eyes is written with a small letter "a". So they show that the sign of brown-eyedness is dominant, and the blue color is a recessive.

So, on the basis of people can be:

• dominant homozygotes (AA, brown-eyed);
• heterozygotes (Aa, brown-eyed);
• recessive homozygotes (aa, blue-eyed).

According to this principle, the interaction of genes with each other is studied, and several pairs of genes are usually used at once. This raises the question: what is genotype 3 (4/5/6, etc.)?

This phrase means that three pairs of genes are taken at once. The entry will be, for example, this: AaVVSs. New genes appear here that are responsible for completely different traits (for example, straight hair and curls, the presence of protein or its absence).

Why is a typical genotype record conditional?

Any gene discovered by scientists has a specific name. Most often these are English terms or phrases that can reach considerable lengths. The spelling of names is difficult for representatives of foreign science, so scientists have introduced a simpler record of genes.

Even a high school student can sometimes know what genotype 3a is. Such a record means that 3 alleles of the same gene are responsible for the gene. When using the actual name of the gene, understanding the principles of heredity could be difficult.

If we are talking about laboratories where serious karyotype and DNA studies are carried out, then they resort to the official names of genes. This is especially true for those scientists who publish the results of their research.

Where are genotypes used?

Another positive feature of using simple notation is its versatility. Thousands of genes have their own unique name, but each of them can be represented by only one letter of the Latin alphabet. In the overwhelming majority of cases, when solving genetic problems for different signs, the letters are repeated again and again, and each time the meaning is deciphered. For example, in one task, gene B is black hair, and in another, it is the presence of a mole.

The question “what are genotypes” is raised not only in biology classes. In fact, the conventionality of designations causes the fuzziness of formulations and terms in science. Roughly speaking, the use of genotypes is a mathematical model. In real life, everything is more complicated, despite the fact that the general principle still managed to be transferred to paper.

By and large, genotypes in the form in which we know them are used in the program of school and university education in solving problems. This simplifies the understanding of the topic “what are genotypes” and develops students' ability to analyze. In the future, the skill of using such a notation will also be useful, but in real research, real terms and gene names are more appropriate.

Genes are currently being studied in various biological laboratories. Encryption and use of genotypes is relevant for medical consultations when one or more traits can be traced through a number of generations. At the output, specialists can predict the phenotypic manifestation in children with a certain degree of probability (for example, the appearance of blondes in 25% of cases or the birth of 5% of children with polydactyly).

Hello dear blog readers Skype biology tutor .

This is how “parsley” turns out, 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 name this article at first "Phenotype and genotype". It is clear that the phenotype is secondary to the genotype. But if the term “genotype” itself can most often be interpreted correctly by students, then, as it turns out, there is no clear idea about the concept of “phenotype”.

But how can he be “clear”, if the definitions of the phenotype in the educational literature are so vague.

"Phenotype- the totality of all external signs of the organism, determined by the genotype and environmental conditions. Or "A phenotype is a set of all external and internal signs and properties of an organism, depending on the genotype and environmental conditions."

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

Still, you have to start not with the “tail”, but with 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 interchangeably.

They say, “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 to the definition of the genotype that such a definition introduces additional confusion. Yes, indeed, information about any trait is encoded in some gene (or set of genes) of the organism.

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

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

Thus, if one correctly understands 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 "the phenotype is the totality of all the genes realized during the life of the organism, which served to form specific features of the given organism in certain environmental conditions."

Therefore, throughout the life of the 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?

reaction rate

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

To better understand what is meant by the concept of "reaction rate", let's look at specific examples of the possible manifestation of a "broad" or "narrow" reaction rate.

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

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

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

Potato example. It is obvious to anyone that the “tops” have a rather narrow reaction rate, and the mass of tubers is very wide.

I think it's all sorted out now. The genotype is the set of all the genes of an organism, this is its entire potential for what it can be capable of in life. And the phenotype is only a manifestation of a small part of this potential, the realization of only a part of the organism's genes into a number of specific traits during its life.

A good example of the realization during the life of an organism of a part of its genotype into a phenotype are identical twins. Having absolutely the same genotype, in the first years of life they are almost indistinguishable from each other phenotypically. But growing up, having at first slight differences in behavior, in some attachments, giving preference to one or another type of activity, these twins become quite distinct and 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 those who study the basics of genetics has, as it were, two meanings. Above, we analyzed the meaning of "genotype" in its broadest 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, we also have a truncated phenotype, we say “the phenotype of an organism”, and we ourselves have studied the mechanism of inheritance of only one or two of its features. 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 of "genotype" and "phenotype", it would be appropriate here to analyze the question of hereditary and non-hereditary forms of variability in organisms. Well, okay, we’ll just talk about this in.

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