genetics
Genetics is the science of heredity and variability of organisms. Genetics is based on the laws of inheritance, according to which all the main characteristics and properties of an organism are determined by individual hereditary factors localized in specific cell structures - chromosomes (see). Direct carriers hereditary information are molecules of nucleic acids (see) - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Genetics studies the nature of the material carriers of heredity, possible ways and their methods artificial synthesis, mechanisms of action, changes and reproduction, control of these functions, formation complex properties and signs whole organism, the relationship of heredity, variability, selection and evolution.
The main method of research in genetics is genetic analysis, which is carried out at all levels of the organization of living matter - molecular, chromosomal, cellular, organismal, population and, depending on the purpose of the study, is divided into a number of private methods - hybridological, population, mutation, recombination, cytogenetic, etc. .
The hybridological method, through a series of crossings (direct or reverse), makes it possible to establish patterns of inheritance of individual characteristics and properties of an organism. The laws of inheritance of a trait at the population level are determined using population analysis. Both of these methods often include elements of mathematical statistics.
Using mutation and recombination methods, the structure of material carriers of heredity, their changes, mechanisms of functioning and exchange of genes are analyzed during crossing and whole line other questions. Cytogenetic method, which combines the principles of cytological and genetic tests, allows us to get an idea of the “anatomy” of the material carriers of heredity. Genetics uses cytochemical, biophysical, electron microscopic and other research methods.
Depending on the object and method of research, a number of independent directions have emerged in genetics: molecular genetics, biochemical genetics, medical genetics, population genetics, radiation genetics, genetics of microorganisms, animals, plants, cytogenetics, immunogenetics, etc.
Medical genetics studies the patterns of human pathological heredity. Despite a certain overlap in areas of research, medical genetics should be distinguished from anthropological genetics, which studies the inheritance of normal variations in structure and morphological features person.
Medical genetics combines the principles and methods of genetics and medicine. The subject of her research is the connection between heredity and pathology caused by various disorders material carriers of heredity - chromosomes and genes. Such changes can be gene mutations, deletions, translocations, chromosome nondisjunction, etc. (see Variability).
To the field of research medical genetics includes patterns of transmission of pathological traits to offspring, questions of etiology, pathogenesis and prevention of hereditary diseases, questions of the causality of human pathological variability. Medical genetics also studies genetically determined predisposition to diseases, the occurrence, development and severity of which depend on environmental conditions (hypertension, diabetes, etc.), genetically determined resistance to certain diseases (resistance to malaria, etc.).
Medical genetics uses a number of special methods research: genealogical (analysis of the inheritance of pathology by pedigree), twin (analysis and comparison of the development of twins depending on living conditions), population-statistical (distribution of a trait within a population) and some others.
The main task of medical genetics is to reduce the number of hereditary diseases, which is achieved by early warning of the development of certain hereditary diseases (phenylketonuria, galactosemia, etc.), identifying hidden carriers of a pathological trait, determining the genetic danger of a number of factors external environment(radiation, physical and chemical factors) and eliminating their influence.
At one time, a network of medical genetic consultations was created in the Soviet Union, where geneticists could give qualified advice regarding the prognosis of morbidity in families with congenital developmental defects and hereditary diseases, and also contribute early detection carriers of pathological genes among the population.
See also Heredity.
Genetics of microorganisms a branch of genetics that studies the variability and heredity of microorganisms. This includes the genetics of bacteria, the genetics of viruses, the genetics of fungi, etc.
The genetics of microorganisms studies heritable changes in the properties of microbes that arise spontaneously ( spontaneous mutations) or as a result of various chemical and physical influences(induced mutations), as well as processes of exchange of genetic material between microorganisms, structure. and the function of their genetic apparatus.
The exchange of genetic material in bacteria is carried out by three different ways: 1) transformation of bacteria; in this case, part of the genes of the donor bacterium is introduced into the recipient bacterium in the form of an isolated DNA molecule; 2) transduction of bacteria; in this case, the role of a carrier of genetic material between the cells of the donor and recipient is performed by temperate bacteriophages. The first and second methods do not require direct contact between the donor and the recipient; 3) conjugation of bacteria; in this case, the exchange of genetic material occurs at the moment of direct contact between the donor and the recipient. After the donor’s genetic material enters the recipient bacterium, the actual genetic exchange occurs: recombination between DNA molecules. Genetic exchange in viruses occurs when two or more viral particles reproduce together within one cell.
Success modern genetics microorganisms made it possible to explain a number of phenomena and processes important for practice. The mechanisms of formation of drug resistance in bacteria have been elucidated and ways to eliminate it have been outlined. Mutants were obtained - active producers of antibiotics, vitamins and amino acids, important for medical and economic practice.
Radiation genetics- a branch of genetics devoted to the study of the effect of radiation on hereditary structures. As a result of exposure to ionizing radiation or ultraviolet rays mutational changes occur in chromosomes, manifested in structural rearrangements of chromosomes and in point mutations that change functional properties genes. The frequency of mutations depends on the radiation dose, as well as on the irradiation conditions; for example, the presence of oxygen in the environment dramatically increases biological efficiency x-rays. Radiation mutations arise as a result of damage to chromosomal DNA, both directly through the entry of energy quanta into the chromosomes, and through the formation of various active products in the cell.
Mutations that occur in somatic cells can cause changes in the irradiated organism - lead to leukemia, malignant tumors, accelerate the aging process, and also cause temporary or permanent sterility. Mutations in germ cells can manifest themselves as hereditary abnormalities in subsequent generations of organisms.
Protecting human heredity from the damaging effects of radiation is the most important practical task radiation genetics. There are currently a number of chemical compounds, which can significantly reduce the mutagenic effect of radiation when administered before or after irradiation.
IN last years It has been established that in animal and human cells there are special enzyme systems that can eliminate some of the damage hereditary structures, caused ionizing radiation and ultraviolet rays.
Genetics is a branch of biology that studies material basis heredity and variability and mechanisms of evolution of the organic world.
The founder of genetics is considered to be Gregor Mendel, the abbot of a monastery in Brno (Czech Republic), who proposed a hybridological method for studying heredity and discovered the laws of independent inheritance of traits. These laws are named after Mendel. They were rediscovered at the beginning of the 20th century, and explained in the middle of the century, after the discovery and study of nucleic acids, including DNA.
The most important concepts of genetics include heredity, variability, gene, genome, genotype, phenotype and varieties of the gene pool.
Let's consider the listed concepts in more detail.
Heredity is the ability of parents to transmit to their offspring certain traits that are strictly characteristic of these organisms. Thus, the offspring of plants cannot be animals; a palm tree cannot develop from wheat seeds, etc.
There are several types of heredity.
1. Nuclear heredity, which is determined by the genome of the cells located in the nucleus (about the genome, see below). This type of heredity is the most common and characteristic of all eukaryotes.
2. Cytoplasmic heredity, determined by the genome located in the cytoplasm (in plastids, mitochondria, cell center etc.). An example of this heredity is the variegation of the Night Beauty violet, determined by the variegation gene located in the cytoplasm of the egg.
The role of heredity is that it:
1) ensures the existence of this species during a certain historical period of time;
2) consolidates those characteristics of organisms that arose due to variability and turned out to be favorable for the existence of the organism in a given environment.
Variability is the ability of different individuals of a given species to exhibit characteristics that distinguish these organisms from others.
In nature, no two organisms are exactly alike. Even twins that develop from the same egg have characteristics that distinguish them from each other. There are several types of variability.
1. Modification (specific, group) variability is, as a rule, morphological variability (changes in the size of an organism depending on living conditions, individual parts of the organism - leaves, flowers, stems, etc.). The reason for such variability is quite simple to establish (hence the name “definite”). Since conditions affect organisms in approximately the same way, then different individuals of the same species will have approximately the same changes (this explains the name “group”). It is important to know that modification variability does not affects a hereditary substance (genotype), therefore it is not inherited and is also called “non-hereditary”.
2. Mutational (hereditary, indeterminate, individual) variability is associated with changes in the hereditary substance. It is possible to establish the cause of such variability, but it is very difficult, hence the name “uncertain”. This variability affects separate organism, even its individual parts, hence the name “individual”. Mutational variability is inherited by the organism, and if the resulting change is favorable for its survival, then such a change is fixed in the offspring, if not, then the carriers of the resulting characteristics die.
Mutational variability is heterogeneous and has a number of varieties:
1. Chromosomal variability is associated with changes in the structure of chromosomes. One of its types is combinative variability, which arises due to crossing over.
2. Gene variability is associated with a violation in the structure of the gene.
Any mutational variability is associated with a change in the genotype, which in turn leads to a change in phenotype. Mutational variability manifests itself in different forms of mutations, among which the following are distinguished:
1. Polyploidy - a multiple increase in the number of chromosomes; observed mainly in plants; it can be induced artificially, which is widely used in breeding to overcome barriers during interspecific crossing (this is how triticale, wheatgrass-wheat hybrid, etc. were obtained).
2. Somatic mutations - changes that occur due to various modifications in the chromosomes of somatic cells (this leads to a change in only part of the organism); these mutations are not inherited, since they do not affect the chromosomes of gametes. Somatic mutations can be used in the selection of organisms that reproduce vegetatively (this is how the Antonovka six-hundred-gram apple tree variety was bred).
The role of variability is that it:
1) ensures better adaptability of the body to environmental conditions;
2) creates the prerequisites for the implementation of microevolution, since gene mutations in germ cells lead to the emergence of characteristics that sharply distinguish one organism from another, and if such characteristics turn out to be favorable for the organism, they are fixed in the offspring, accumulate, which ultimately leads to the appearance new species.
A gene is a section of a DNA molecule responsible for the presence and transmission of a specific trait of an organism.
A genome is the collection of all genes in a given organism.
Genotype. Distinguish between genotype in a broad and narrow sense this term. IN in a broad sense genotype is the totality of all genes contained in the chromosomes and cytoplasm of the cell of a given organism, which determine the characteristics of the organism and transmit them to inheritance.
In genetic studies, the concept of “genotype in” is often used. in the narrow sense words" - when, when characterizing an organism, they talk about genes that characterize one or more characteristics selected for research (for example, the genotype of peas with green seeds). In research, the use of genotype in the broad sense of the word is almost impossible, since difficulties arise with processing the experimental results.
The genotype (in general) for organisms of a given species is almost the same - with some small differences that characterize the individuality of this particular organism.
The gene pool of a species is the totality of all genes in all individuals belonging to a given species.
The gene pool of a biocenosis is the totality of all genes belonging to all organisms that form a given biocenosis.
The gene pool of the planet is the totality of all genes of all individuals of all species inhabiting the planet.
Phenotype. Phenotype, like genotype, is distinguished in both the broad and narrow sense of the term.
Phenotype in a broad sense means the totality of all signs and properties of organisms developing during the life process in specific environmental conditions, formed on the basis of the genotype under the influence of external environmental conditions.
Based on the phenotype as a whole, it is impossible to establish patterns of inheritance of certain characteristics, since there are a lot of them and they are closely intertwined with each other, therefore it is necessary to distinguish the concept of “phenotype” in the narrow sense of the word.
Phenotype in the narrow sense means one or more specific characteristics that characterize given organism(the number of such signs does not exceed three or four). Thus, peas can be characterized by wrinkled green seeds (two characteristics are used here). Each trait is associated with a material carrier (gene) of this property body.
Variations exist when the phenotype is strictly related to a given genotype. For example, green color pea seed is determined only by the gene for the green color of the seed. There are also cases when a given phenotype is associated with a different genotype, for example, the yellow color of a pea seed can be determined either by genes yellow color seed, or a combination of the yellow gene and the green gene of the seed, i.e. One phenotype may correspond to several genotypes (in the narrow sense of these terms).
General characteristics of research methods used in genetics
The patterns of inheritance of traits by organisms make it possible to control these processes during selection, which contributes to the significant development of this area of knowledge.
There are several stages in the development of genetics.
The first stage (1865-1903) is characterized by the beginning of research and the laying of the foundations of genetics. The founder of the doctrine of the laws of inheritance, G. Mendel, proposed and widely used the hybridological method of research and was the first to discover the laws of independent inheritance of characters. Mendel's laws were rediscovered by G. de Vries, K. Correns and E. Cermak. In 1900, V. Johansen first formulated the concept of “population” and instead of the concept of “hereditary factor” he introduced the concepts of “gene”, “genotype”, “phenotype”. At that time, the material basis of the gene was unknown, which led to the underestimation of genetics by materialists.
The second stage in the development of genetics (1903-1940 of the 20th century) is associated with the study of problems of genetics in cellular level. Highest value There were works by T. Boveri, W. Setton and E. Wilson, who established the relationship between G. Mendel’s laws and the distribution of chromosomes in the process of mitosis and Meiosis. T. Morgan discovered the law of “linked inheritance” and explained it from the standpoint cell theory. A convenient object was found genetic research- Drosophila fruit fly. N. I. Vavilov discovered the law homologous series inheritance.
The third stage in the development of genetics begins in the 40s of the 20th century. and continues to this day. At this stage, genetic patterns are studied and explained in molecular level. At this time they were open nucleic acids, their structure was established, the material basis of the gene as a carrier of heredity was revealed, principles were developed genetic engineering, genetics has become scientific basis selection, which is its main practical significance.
Widely used in genetics following methods research.
1. The hybridological research method consists in taking organisms with sharply various signs of this type, for example, plants with white and red flowers, seeds of different shapes or colors, animals with different lengths hairline or different colors wool, etc. These organisms are crossed and the pattern of inheritance of different traits by offspring is studied.
There are monohybrid, dihybrid and polyhybrid crossings (di-, tri-, tetra- and further are variants of polyhybrid crossing).
In monohybrid crossing, organisms that differ in characteristics of the same type are studied, for example, plants are crossed with flowers different color or with seeds different shapes or cross polled (hornless) goats with horned ones, etc.
In a dihybrid cross, organisms that have different signs two types, for example, crossing peas with smooth and yellow seeds with peas whose seeds are green and wrinkled, or crossing animals with long black hair with animals that have short and White wool, etc.
The hybridological method of genetic research is applicable and quite effective for organisms that produce large fertile offspring and which often enter into reproduction processes (plants with short term development, insects, small rodents, etc.).
2. Genealogical method Research in genetics consists of studying the pedigree lines in the offspring. For animals, these are breeding books of offspring; for people, these are patrimonial books of aristocrats, where the descendants of various tribes are indicated and noted the most important signs, including diseases.
This method is used in the study of patterns of inheritance in humans and large animals that produce few offspring and have long period reaching puberty.
3. The twin method of genetic research is associated with the study of the influence environment on organisms with very similar genotypes (in broadly understood this term). This method is closely related to the genealogical method and is applicable to study the characteristics of inheritance of the same organisms as the genealogical method.
To understand the laws of inheritance, you need to know some terms. These terms are discussed below.
The most important concept of genetics is the gene, which is a unit of hereditary information and determines the nature of inheritance and the possibility of developing a trait. In the haploid set of chromosomes (the genome of prokaryotes or germ cells) there is one gene that determines one or another trait. Somatic cells contain a diploid set of chromosomes, there are homologous chromosomes, and each type (type) of a trait is determined, as a rule, by two genes.
Varieties of the same type of trait that are mutually exclusive are called alternative (for example, yellow and green seed colors, long and short hair).
Genes, based on the nature of their location on chromosomes and the characteristics for the development of which they are responsible, are divided into allelic and non-allelic.
Allelic are genes that are located in the same loci of homologous chromosomes and control the development of alternative traits (for example, genes for the smooth and wrinkled surface of a pea seed).
Non-allelic genes control various non-alternative traits; they can be located both on the same and on different chromosomes (for example, genes for yellow seed color and smooth seed surface shape).
Allelic genes, according to the nature of their influence on each other, are divided into three types: dominant (suppressing), recessive (suppressed) and equivalent (equivalent, genes of the same effect).
Dominant are those allelic genes that suppress the manifestation of another alternative trait for which another allelic gene is responsible (for example, the gene for yellow seed color suppresses the gene for green seed color and the newly emerged offspring will have yellow seeds). These genes indicate in capital letters Latin alphabet, for example A, B, C, etc.
Recessive are those allelic genes whose effect is not manifested in the presence of other paired genes of the corresponding alternative trait (for example, the gene for the wrinkled shape of a pea seed does not manifest itself in the presence of a gene for a smooth shape of a pea seed, due to which in plants obtained after crossing plants with smooth and wrinkled surface of the seed, there will be seeds with a smooth surface). These genes indicate lowercase letters Latin alphabet, for example A 1 and A 2; B 1 and B 2, etc.
Genes of equal influence are those allelic genes that, when exposed to each other, produce intermediate characteristics (for example, the genes for the white and red color of the petals of the Night Beauty violet flower, being in the same organism, lead to the appearance of plants with pink flowers). They are designated by capital letters of the Latin alphabet with an index, for example A 1 and A 2; B 1 and B 2, etc.
Organisms, somatic cells which contain the same allelic genes are called homozygous (for example, AA, bb or AABB, etc.).
Organisms whose somatic cells contain different allelic genes are called heterozygous (they are designated AA, Bb, AABB).
Recessive traits (characters for which they are responsible recessive genes) appear only in homozygous organisms containing two identical allelic gene, responsible for the recessive trait.
Evolutionary theory and genetics
Genetics has a major influence on the understanding and explanation of many issues in evolutionary theory. Thus, without the ideas developed by genetics, it is impossible to explain the cause of evolution. The concept of an “ideal population” explains a lot in explaining the foundations of evolutionary theory.
Population genetics is closely related to evolutionary theory. Her the most important concept is an ideal population - a hypothetical population incapable of real existence due to the fact that no new mutations arise in it, there is no selection favoring (unfavorable) certain genes, and the possibility of a random combination of genes is provided (due to large size population) that is completely isolated from the influence of other populations.
For ideal populations, the Hardy-Weinberg law (1908) is valid: In an ideal population, with free crossing, the relative frequencies of genes (frequencies of homo- and heterozygotes) do not change for all subsequent generations.
In real populations, this law is not implemented, since the occurrence of mutations is inevitable due to constantly changing micro- and macroconditions. In these populations there is constant interbreeding and selection.
Due to crossing with relative phenotypic homogeneity, the accumulation of individuals with recessive characteristics occurs and at a certain stage it becomes possible to cross organisms with such characteristics that are phenotypically manifested, which leads either to the consolidation of these characteristics as a result natural selection, or to extinction, which creates the basis for the processes of speciation.
Consequently, each species and each population is a complex heterozygous system, which contains a reserve of hereditary variability that creates the basis for evolutionary processes(from microevolution to macroevolution).
A geneticist is a specialist whose responsibilities include identifying, treating and preventing hereditary diseases. This specialist also deals with a person’s genetic predisposition to certain pathologies. To put it simply in simple words, this doctor specializes in health problems that are passed on to a child from parents.
To become a geneticist, first of all, you need to obtain higher education in the field of general medicine. After this, you need to undergo specialization in genetics, which is carried out at departments for training geneticists at different educational institutions. Specialization training lasts approximately 2 years.
A geneticist is a specialist who is involved in determining the genetic nature of a particular disease. This specialist is engaged in identifying and treating not just a large, but a truly huge number of diseases. It is impossible to list them all, but let us note at least some of them: Down syndrome, Ehlers-Danlos syndrome, cystic fibrosis, Wolf-Hirschhorn syndrome, cry-the-cat syndrome, myotonic dystrophy, mutations and many others.
What are the responsibilities of a geneticist?
This specialist must first of all accurately deliver. Then he should identify the type of inheritance in each specific case. His responsibilities include calculating the probability of the risk of relapse of a particular disease. It is this specialist who can determine one hundred percent whether preventive measures can or cannot help prevent the development of a hereditary disease. He must also clearly explain all his thoughts to the patient, as well as to his family members, if any, at his appointment. Well, and, of course, this is exactly what a specialist should conduct, if necessary, all the necessary examinations.
In what cases is a visit to a genetics doctor mandatory?
If for a married couple it has special meaning gender of the child, then they should visit this specialist. The same should be done for all those families who had or have hereditary diseases or deformity. The presence of a child with genetic disorders in the family is another reason to make an appointment with this doctor. You cannot do without the help of this specialist in the case of consanguineous marriages, as well as if a woman becomes pregnant over the age of thirty-five.
The reasons for the development of genetic skin diseases are very numerous. The fact is that every person’s skin is exposed to a number of environmental factors every day. It is influenced not only Sun rays and air, but also numerous fungi, bacteria and many other microscopic organisms. All these factors, of course, can trigger the development anomalous phenomena. Since the skin is a kind of protection internal organs, any skin diseases immediately affect the system of the entire body as a whole. As for genetics, then scientific research It has been proven more than once that numerous skin diseases tend to be inherited.
So, for example, if both parents have a disease such as atopic, then the risk of the same disease in their child reaches sixty to eighty percent. If only one parent has this pathology, then atopic dermatitis can occur only in fifty percent of cases. There are also situations when this disease is observed in a child, but his parents are completely healthy, but one of his relatives has atopic dermatitis. Very often, skin pathologies such as acne are inherited. If the parents have excessive acne, then most likely this problem will also bother their beloved child.
In conclusion, we note that hereditary predisposition to certain ailments is just a predisposition, but not the disease itself. That is why children need to be taught from childhood and then, perhaps, they will be able to avoid all these troubles.
Almost every living cell of the human body contains a certain amount of information, which tends to regulate its performance, as well as cellular production throughout life. This information is a kind of “code” that all other cells that are descendants of the first receive. In fact, this “code” is hidden directly in the chromosomes, which are located in the cell nucleus. Normally, the human body should have twenty-three pairs of such chromosomes. The last twenty-third pair determines the gender of the person. In turn, each chromosome consists of numerous genes, which represent the basic hereditary unit. Genes are also assigned certain functions. They are responsible for eye color, ear shape, hair quality, and so on.
What are real reasons development of genetic diseases?
Certain hereditary diseases can arise for several reasons. In most cases, they arise due to a chromosome or gene defect. This defect can be inherited, or it can be acquired. Genetic disorders can be of several types - these are autosomal dominant, autosomal recessive, and x-linked gene defects. Quite often, this type of disease occurs as a result of genetic defects that arose against the background of the interaction of genes with unfavorable factors environment. Very often, this type of change is the result of a change in the structure or number of chromosomes.
Most likely, many of you will agree that the birth of a child with a rather complex disease very often forces parents to make a choice. Some of them leave the baby and provide him with full care. Others send such children to special orphanages. In principle, we will not condemn anyone, since each person himself has the right to decide which one life path he needs it. There are also cases when sick children remaining in orphanages acquire new parents after some time, even despite the fact that they have some rather serious pathology.
What genetic diseases are the most common in adopted children?
According to statistics, the most common hereditary disease of such children is considered to be Down syndrome. This disease is genetic. If it is present, the child has forty-seven chromosomes. This pathology is observed equally often in both boys and girls. Another fairly common genetic disease is considered to be Shereshevsky-Turner disease. Only girls can get this disease. But boys can experience such a disease as Klinefelter's disease. It should be noted that Shereshevsky-Turner disease in most cases makes itself felt only at the age of eleven to twelve years. Even later, Klinefelter's disease can be detected. In boys, it develops only at the age of sixteen, and sometimes even at the age of eighteen.