Genotype: what it is, types, how it differs from phenotype

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In 1909, Danish biologist and geneticist Wilhelm Johansen introduced the concepts of genotype and phenotype. Without knowledge of these terms it is impossible to study genetics.

The material was prepared jointly with a teacher of the highest category, candidate of biological sciences Faktorovich Liliya Vitalievna.

More than 31 years of experience as a biology teacher.

Basic concepts of genetics

In addition to these two concepts, the basic concepts of genetics include others:

1. Heredity is the transfer of characteristics from one living organism to another;
2. Variability is the process of the offspring acquiring distinctive characteristics during individual development;
3. Allelic gene – a gene that occupies identical loci in homologous chromosomes;
4. Heterozygote is an individual that carries a gene of a different molecular structure;
5. Homozygote is an individual that carries a gene with the same molecular structure.

Examples of genotype

Eye color

Although a given genotype is made up of many nucleic acids, scientists typically represent genotypes with one letter or two letters in the case of sexually reproducing organisms that receive one allele from each parent. For example, the sign of eye color can be represented by the letter "E". Varieties or alleles of this trait that are dominant will be indicated by capital letters. Therefore, "E" would represent brown eyes. Recessive traits are written in lowercase. The allele for blue eyes is recessive to the allele for brown eyes, so we can call it "e".

Many parents have brown eyes. Having brown eyes only tells us their phenotype, not their genotype. Parents can be "Ee", "EE" or one of these. One "E" allele in the genotype will result in a brown-eyed phenotype, even if the parent also has the recessive "e" allele. Parents conceive a child. The child has blue eyes. This tells us that the child is homozygous recessive or "uh" because only two recessive alleles can produce blue eyes. It also tells us a lot about the parents. A child with two "e" alleles received one from each parent. Thus, each parent has one allele "e" which it can produce, having the brown eyed phenotype. This shows us that the parents have a heterozygous Genotype “Ee”. If either parent was homozygous dominant, "EE", the child would have received at least one dominant "E" allele, giving him brown eyes.

Cystic fibrosis

For a long time, it was not known why some children develop thick mucus in their airways, causing them to become short of breath and short of breath. The children had a variety of other symptoms, such as an inability to effectively process food, gas, and weight loss. Before recent advances in medicine and genetics, many children died at a very young age. After several years of research, it was discovered that cystic fibrosis is caused by a defect in the gene that produces salt channels through the cell membrane. These salts, or ion channels, are used to maintain pH levels in various cells, remove waste, and remove nutrients from the intestines.

The genotype of people with cystic fibrosis is homozygous recessive. In other words, they carry two copies of a nonfunctional allele for a gene that creates specific ion channels. Some people, known as "carriers", may have a functioning normal phenotype when heterozygous. This means that the carrier can pass on the non-functional allele to their child. Not knowing that two carriers can both pass on a non-functioning allele to a child with a non-functioning homozygous recessive genotype. However, if one or both carrier parents pass on their good allele, the child will not have symptoms of cystic fibrosis. If a child receives one functioning allele and one non-functioning allele, he will also be a carrier. A child will not be a carrier if he receives two functional alleles.

However, for parents who are carriers, the genotypic ratio in the offspring will be 1 normal: 2 carriers: 1 cystic fibrosis genotype. This genotypic ratio can be calculated in Punnett Square. Place the heterozygous parents on the sides of the square, separating their individual alleles (Aa and Aa below). Then simply fill in the fields with the two alleles that each potential child will receive. This can be quickly seen by calculating that the genotypic ratio is 1AA: 2Aa: 1aa. In this case, the phenotypic ratio will be 3 normal: 1 cystic fibrosis.

• dominant – Having the ability to mask the effects of a recessive allele,
• Recessive - An allele that exhibits phenotypic effects only in the presence of another recessive allele.
• heterozygous – A genotype containing two types of alleles.
• Homozygous - A genotype containing one type of allele.

Genotype: what is it?

Genotype is a set of genes of one organism inherited from its parents. It represents the entirety of the genetic information that we have, and we can pass it on to our descendants. A child from his parents has a set of genes: half from the father and half from the mother, therefore, he will look like them, but will not become an exact copy.

When studying the genotype, it is important to know the concept of “gene”. A gene is a molecular system that contains information about the functions of the body and acts as a structural unit of heredity. If you imagine a DNA molecule, then a gene is a section in this molecule that carries information about its primary structure.

The genotype is a complex system called the genetic environment, where individual genes depend on each other. It also carries genetic information, with the help of which it controls the structure and development of the body. The genotype is transmitted in the form of a genetic code that is present in all cells of the body and, during division or reproduction, transmits hereditary information to the offspring.

“To determine your set of genes, you need to take tests for research”

Genotype, genome and gene pool

The term “genome” was proposed by the German biologist G. Winkler 10 years later than the concept of “genotype” was formulated.

Genome also refers to a collection of genes , but unlike a genotype, a gene is considered here as a nucleotide sequence of DNA in haploid cells (with a single set of chromosomes), and not as an allele (an alternative form of the same gene) in a diploid set of chromosomes.

In order not to get lost in the jungle of genetics, it is important to understand the main thing :

The genotype is an individual characteristic (individuals of the same species with the same set of genes can differ in allelic characteristics), while the genome is a species characteristic (individuals of the same species have a set of identical genes).

The genome , being the hereditary material of an organism, is stored in several (sometimes in one) chromosomes, the number of which is unique for a particular species.

The genome size (based on the number of genes it contains) varies widely, reaching several tens of thousands of units. The fewest genomes were found in the simplest viruses (several hundred), the largest number were found in representatives of the plant world (for example, there are more than 46,000 of them in rice).

According to recent studies, the human genome consists of 46 chromosomes (23 pairs), which contain about 22-25 thousand genes.

The gene pool is the totality of all genotypes in individuals of a certain population; it encodes genetic memory, which is passed on from generation to generation.

Individuals from different populations can interbreed and produce offspring. The gene pool of a species is made up of the gene pool of populations.

The characteristic features of the gene pool include the following distinctive qualities:

1. Under constant environmental conditions, the gene pool remains unchanged.
2. When external conditions change, individuals whose genes possess traits useful for survival gain an advantage. It is these individuals that will pass on the most valuable qualities to their offspring during sexual reproduction.
3. The genes responsible for the most “advantageous” traits accumulate from generation to generation, creating the basis for changes in the gene pool.
4. The variability of the gene pool as a mechanism of natural selection is directional and helps to improve the adaptive functions of the body.

The evolutionary changes occurring in the population can be traced in the following examples. In harsh climatic conditions (extreme cold, heat), the proportion of genotypes that increase the thermal insulation of organisms increases.

In other cases, the preservation of a population largely depends on genes encoding the color of the animal (in order to improve camouflage), or the synthesis of protective enzymes (liquids, gases), or behavior patterns, etc.

All this makes the population (or species as a whole) more resistant to the external environment, and therefore ensures its survival.

A person, like most living organisms, receives his genotype from his parents , which determines the natural properties of a person, primarily the structure of the body and the functioning of the brain.

It happens that some genes (in parents or their descendants) turn out to be damaged (mutated), but this has practically no effect on the genotype, since mutations caused by such genes are unstable and are almost never repeated in inheritance. It follows that the human genome is absolutely stable.

Recording genotypes

Genotypes are studied by coding genes (for example, the gene for blond hair is written “A”, and the gene for dark hair “a”). This designation in large and small letters shows which gene is dominant and which is recessive.

Following this principle it is possible:

1. Dominant homozygotes (AA blonde);
2. Heterozygous (Aa blonde);
3. Recessive homozygotes (aa dark-haired).

The interaction of genes is studied using the same principle. They just take several pairs of genes, which is where terms like 2,3,4,5 genotype come from. If you take three pairs of genes, the entry may look like AABbCc; if you take five pairs of genes, then two more designations will be added to the entry. Each gene is responsible for its own trait: blue or green eyes, the presence or absence of protein.

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 just one letter of the Latin alphabet. In the overwhelming majority of cases, when solving genetic problems for various traits, the letters are repeated again and again, and the meaning is deciphered each time. For example, in one problem, gene B is the color of 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 convention of designations causes the vagueness 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 was nevertheless transferred to paper.

By and large, genotypes in the form in which we know them are used in the curriculum of school and university education when 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 for real research, real terms and gene names are more appropriate.

The genes are currently being studied in various biological laboratories. Encryption and use of genotypes is relevant for medical consultations when one or more characteristics can be traced over a number of generations. As a result, experts can predict the phenotypic manifestation in children with a certain degree of probability (for example, the appearance of blond hair in 25% of cases or the birth of 5% of children with polydactyly).

Genotype variability

Changing the set of genes is only possible through mutations that occur for reasons such as radiation and the influence of chemicals. In this case, the DNA structure changes and is further passed on to inheritance.

Mutations can be:

1. Genomic (change in the number of chromosomes)
2. Chromosomal (modification of chromosome structure);
3. Genetic (changes in the structure of one gene);
4. Spontaneous (can occur independently throughout life);
5. Artificial (specially called in the laboratory).

Mutations are rarely beneficial for the body; they can even be lethal.

How is a person's genotype formed?

What is a genotype in biology? Initially, it was assumed that the set of genes of each cell in the body is different. This idea was refuted from the moment scientists discovered the mechanism of formation of a zygote from two gametes: male and female. Since any living organism is formed from a zygote through numerous divisions, it is not difficult to guess that all subsequent cells will have exactly the same set of genes.

However, it is necessary to distinguish the genotype of the parents from that of the child. The fetus in the womb has half the set of genes from mom and dad, so although children are similar to their parents, at the same time they are not 100% copies of them.

Types of genotypes

The expression of a gene depends on the genotypic environment. Therefore, in the genotype according to the type of interaction they can be:

1. Hypostatic (suppressed by genes of another allelic pair):
2. Pleiotropic (affect the manifestation of several signs at once);
3. Epistatic (suppress the action of non-allelic genes);
4. Sublethal (causes the death of an individual before the start of the reproductive period);
5. Lethal (reduce the viability of the embryo even to its death);
6. Modifiers (change the expression of other genes);
7. Mutators (dramatically change the characteristics of an organism).

The existence of different types of genotypes explains the individual reaction of a person, for example, to medications, and explains the different degrees of development of immunity.

Determination of genotype

An organism's genotype is the chemical composition of its DNA that results in the organism's phenotype or observable characteristics.
The genotype consists of all the nucleic acids present in the DNA molecule that codes for a particular trait. Appearance, or phenotype, is the result of the interaction of proteins created by DNA. Modern DNA analysis techniques have made it easier to determine which DNA segments are responsible for different phenotypes. A genotype has different alleles or forms. Different alleles are produced by mutations in DNA and can cause beneficial or harmful changes. In bacteria, the DNA exists in a circle and only one allele for each genotype is present. Someday, the allele will mutate in a favorable form, the organism will reproduce more, and the genotype will increase in population. In sexually reproducing organisms, two alleles are present in each organism, which can have complex interactions with each other and with other genes. Mutations can occur in these alleles, new combinations can arise during meiosis, and an infinite amount of diversity can be created. These genotype combinations give rise to the enormous diversity of life on Earth.

What is a phenotype?

A phenotype is a collection of characteristics that an individual has at a particular stage of development.

“The phenotype is formed on the basis of the genotype”

The set of internal and external characteristics that an organism acquires during its development forms a phenotype. Each organism has its own individual internal and external features: the nature of metabolism, the degree of functioning of the body. This constitutes its phenotype.

What do genes determine?

Currently, molecular biology has established that genes

- these are sections of DNA that carry some kind of integral information - about the structure of one protein molecule or one RNA molecule.
These and other functional molecules determine
the development, growth and functioning of the body.

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Genotype and phenotype: differences

Phenotype is also considered one of the basic concepts of genetics. Genotype and phenotype are closely related, but they also have differences.

Genotype is associated with genetic information, which is learned through special tests and biological studies. A person's phenotype can be seen. It manifests the genetic code and arises during the interaction of the genotype with the external environment (hair color, cut and eye color, face shape).

A person’s phenotype is manifested not only in external signs, but also in internal ones, such as:

1. Biochemical (composition of enzymes and hormones);
2. Anatomical (structure of internal organs);
3. Physiological (cell functioning).

The phenotype is formed under the influence of the environment. This means that different genotypes can produce phenotypes that are similar to each other, and vice versa.

The difference between a phenotype and a genotype is also that the genotype is unchanged, but the phenotype can change throughout life (for example, our hair color may change a little throughout life). It’s the same with the set of genes, it is also constant, but the phenotype changes. If we consider a cell of the body, then each of them carries the same set of genes, but at the same time they will not be similar in shape and size and each plays its own role. This is called phenotypic manifestation.

... 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 in conditions of continuous changes in the space of variations of their genomes. ... ... It is not changes in the genotype that determine evolution and its direction. On the contrary, the evolution of an organism determines the change in its genotype.

Shmalgauzen I. I.

Variability

Each individual is characterized by an individual genotype and phenotype. Genes do not always determine the external and internal structure of the body. For example, genes determine a tendency to obesity, but under the influence of the environment (healthy diet, exercise), obesity is not a feature of the phenotype. Another example: in the course of life, a person broke and changed the shape of his nose. By genotype a person has a straight nose, by phenotype - with a hump.

Variation in phenotype during life is called modification or phenotypic and appears under the influence of environmental factors. It is acquired during life, but is not inherited.

Genotypic variability is of two types:

• combinative - the formation of new sets of genes in the process of meiosis;
• mutational - abrupt changes in genes that are inherited.

Rice.
3. Genotypic variability. Mutations, like phenotypic changes, accumulate throughout life, but are not always reflected in the phenotype. However, they can influence the genotype of subsequent generations.

History of the emergence of concepts

The works of Charles Darwin became the main impetus in the development of the science of heredity and variability. He was the first to put forward the hypothesis of the separation of cells in the body, from which another individual emerges as a result. Thus, Darwin began to develop the theory of pangenesis and his work as a result became the impetus for the development of the science of heredity and variability.

In 1865, G. Mendel managed to formulate the basic laws of genetics by conducting experiments with different varieties of peas: the law of uniformity of first-generation hybrids, the law of segregation, the law of independent inheritance of traits. The date of birth of genetics is attributed to 1900; its term was proposed by W. Batson in 1906. Based on an already known concept, in 1909. Wilhelm Johansen introduced the concept of "gene". Around the same period, he introduced the concept of “phenotype,” thereby emphasizing the hereditary characteristics of genetics.

Later, the German zoologist W. Hacker studied the relationship between the genotypes and phenotypes of organisms, which was later called phenogenetics.

In general, the history of the development of genetics has a rich past; it is divided into three stages:

Stage 1 (1900-1930). The period of classical genetics, Mendelism. Natural discrete heredity has been established. The chromosome theory and the theory of mutations were created.

Stage 2 (1930-1953) . Research was carried out in the field of molecular genetics and the provisions of classical genetics were revised. An integrated approach to research began to be used.

Stage 3 (1953 to present). Decoding the genetic code. The internal and external influences of the variability process are considered. Structural and systemic knowledge of the deep essence of the gene is carried out.

Uncertainty concept

There are some uncertainties in the concept of phenotype. For the most part, molecules and structures, although they are part of the phenotype, are invisible in the external appearance of the organism. Human blood groups precisely characterize this uncertainty. That is why the characteristics detected by medical, technical, or diagnostic procedures should constitute an expanded definition of this term .

Behavior acquired during life, or even the influence of an organism on other organisms and on the environment, in the future, can form the basis for radical expansion. For example, the phenotype of beaver genes, according to Richard Dawkins, can be considered the incisors of beavers, as well as their dam.

The basis of evolution is the variety of different phenotypes. The factors on which their diversity depends, genotype (genetic program), mutations - the frequency of random changes and environmental conditions are given in the following dependence:

phenotype = 1) genotype + 2) external environment + 3) random changes

Phenotypes are sometimes very different in different environments. For example, in open space they are spreading, but in the forest they are slender and tall. Let us highlight a list of characteristics that are determined clinically and are phenotypic:

1. hair shape
2. body mass
3. height
4. eye color
5. blood types

The phenotype is revealed during ontogenesis in given conditions as a result of the interaction of the genotype and external and internal environmental factors. In general, this is what can be heard, felt, seen (the color of the dog) and the behavior of the animal.

In each biological species, you can notice a phenotype that is unique to it, which is formed according to the hereditary information contained in the genes. When the external environment changes, variability arises - individual differences . This occurs because the state of the traits varies from organism to organism. The basis for genetic diversity of forms is variability. There are phenotypic and or genetic variability, as well as modification or mutation.

Modification variability does not cause changes in the genotype; it only shows the maximum capabilities of the organism that has a given genotype. The characteristics of modification variability are quantitative and qualitative deviations from the original norm, which are not inherited, but have only an adaptive nature. For example, a change in the color of a person’s skin due to exposure to sunlight or the development of muscles due to physical activity, etc.

The reaction norm is a term that denotes the extent to which modification variability varies. So, we understand that as a result of the interaction of the genotype and environmental factors, a phenotype is formed. Phenotypic characteristics are not transmitted to offspring from parents, but only the reaction norm is inherited, i.e., the nature of the response to changes in environmental conditions.