1. Genealogical
The genealogical method consists in the analysis of pedigrees and allows you to determine the type of inheritance (dominant
recessive, autosomal or sex-linked) trait, as well as its monogenicity or polygenicity. Based on the information obtained, the probability of the manifestation of the studied trait in the offspring is predicted, which has great importance to prevent hereditary diseases.
As a method of studying human genetics, the genealogical method began to be used only from the beginning of the 20th century, when it became clear that the analysis of pedigrees in which the transmission of some trait (disease) from generation to generation can be replaced by the hybridological method, which is actually inapplicable to humans.
When compiling pedigrees, the source is a person - a proband, whose pedigree is being studied. Usually this is either a patient, or a carrier of a certain trait, the inheritance of which needs to be studied.
Proband - the person from whom the compilation of a pedigree begins during genealogical analysis.
Sibs - one of the children born to the same parents, in relation to other children (for example, a brother or sister).
2. Gemini
This method consists in studying the patterns of inheritance of traits in pairs of identical and dizygotic twins. It was proposed in 1875 by Galton initially to assess the role of heredity and environment in the development of a person's mental properties. At present, this method is widely used in the study of heredity and variability in humans to determine the relative role of heredity and environment in the formation of various signs, both normal and pathological. It allows you to identify the hereditary nature of the trait, determine the penetrance of the allele, evaluate the effectiveness of the action on the body of some external factors ( medicines, training, education).
The essence of the method is to compare the manifestation of a trait in different groups of twins, taking into account the similarity or difference in their genotypes. Monozygotic twins , developing from one fertilized egg are genetically identical, as they have 100% of common genes. Therefore, among monozygotic twins there is a high percentage of concordant steam, in which the trait develops in both twins. Comparison of monozygotic twins brought up in different conditions of the postembryonic period makes it possible to identify signs in the formation of which environmental factors play a significant role. According to these signs, discordance is observed between the twins, i.e. differences. On the contrary, the preservation of similarity between twins, despite the differences in the conditions of their existence, indicates the hereditary conditionality of the trait.
3. Population-statistical
With the help of the population-statistical method, hereditary traits are studied in large groups of the population, in one or several generations. An essential point when using this method is the statistical processing of the obtained data. This method can be used to calculate the frequency of occurrence in a population of various alleles of a gene and different genotypes for these alleles, to find out the distribution of various hereditary traits in it, including diseases. It allows studying the mutation process, the role of heredity and environment in the formation of human phenotypic polymorphism according to normal traits, as well as in the occurrence of diseases, especially with hereditary predisposition. This method is also used to elucidate the significance of genetic factors in anthropogenesis, in particular in racial formation.
4. Dermatoglyphic
In 1892 F. Galton, as one of the methods for studying a person, proposed a method for studying the skin comb patterns of fingers and palms, as well as flexion palmar grooves. He established that these patterns are an individual characteristic of a person and do not change throughout life. Currently, the hereditary conditionality of skin patterns has been established, although the nature of inheritance has not been completely elucidated. Probably, the trait is inherited according to the polygenic type. Dermatoglyphic studies are important in identifying twins. The study of people with chromosomal diseases revealed in them specific changes not only in the patterns of fingers and palms, but also in the nature of the main flexor grooves on the skin of the palms. Less studied are dermatoglyphic changes in gene diseases. Basically, these methods of human genetics are used to establish paternity.
The study of imprints of the skin pattern of the palms and feet. With the existing individual differences in fingerprints, due to the peculiarities of the development of the individual, there are several main classes of them. Peculiar changes in fingerprints and palm patterns have been noted in a number of hereditary-degenerative diseases of the nervous system. Characteristic of Down's disease is a monkey (four-fingered) fold, representing a line passing through the entire palm in the transverse direction. Currently, the method is used mainly in forensic medicine.
5. Biochemical
Hereditary diseases that are caused by gene mutations that change the structure or rate of protein synthesis are usually accompanied by a violation of carbohydrate, protein, lipid and other types of metabolism. Hereditary metabolic defects can be diagnosed by determining the structure of the altered protein or its amount, identifying defective enzymes, or detecting metabolic intermediates in extracellular body fluids (blood, urine, sweat, etc.). For example, analysis of the amino acid sequences of mutated hemoglobin protein chains made it possible to identify several hereditary defects underlying a number of diseases, ? hemoglobinosis. So, in sickle cell anemia in humans, abnormal hemoglobin due to mutation differs from normal by replacing only one amino acid (glutamic acid with valine).
In healthcare practice, in addition to identifying homozygous carriers of mutant genes, there are methods for detecting heterozygous carriers of certain recessive genes, which is especially important in medical genetic counseling. So, in phenotypically normal heterozygotes for phenylketonuria (a recessive mutant gene; in homozygotes, the metabolism of the amino acid phenylalanine is disturbed, which leads to mental retardation), after taking phenylalanine, its increased content in the blood is detected. In hemophilia, heterozygous carriage of the mutant gene can be established by determining the activity of the enzyme changed as a result of the mutation.
6. Cytogenetic
The cytogenetic method is used to study the normal human karyotype, as well as in the diagnosis of hereditary diseases associated with genomic and chromosomal mutations. In addition, this method is used in the study of the mutagenic action of various chemicals, pesticides, insecticides, drugs, etc.
During cell division at the metaphase stage, chromosomes have a clearer structure and are available for study. The human diploid set consists of 46 chromosomes: 22 pairs of autosomes and one pair of sex chromosomes (XX for women, XY for men). Usually, human peripheral blood leukocytes are examined, which are placed in a special nutrient medium, where they divide. Then preparations are prepared and the number and structure of chromosomes are analyzed. The development of special staining methods has greatly simplified the recognition of all human chromosomes, and in conjunction with the genealogical method and methods of cell and genetic engineering, it has made it possible to correlate genes with specific regions of chromosomes. The complex application of these methods underlies the mapping of human chromosomes. Cytological control is necessary for the diagnosis of chromosomal diseases associated with ansuploidy and chromosomal mutations. The most common are Down's disease (trisomy on the 21st chromosome), Klinefelter's syndrome (47 XXY), Shershevsky's syndrome? Turner (45 XO), etc. Does the loss of a segment of one of the homologous chromosomes of the 21st pair lead to a blood disease? chronic myeloid leukemia.
At cytological studies interphase nuclei of somatic cells, you can find the so-called Barry body, or sex chromatin. It turned out that sex chromatin is normally present in women and absent in men. It is the result of heterochromatization of one of the two X chromosomes in females. Knowing this feature, it is possible to identify gender and identify an abnormal number of X chromosomes.
The detection of many hereditary diseases is possible even before the birth of a child. The method of prenatal diagnosis consists in obtaining amniotic fluid, where the cells of the fetus are located, and in the subsequent biochemical and cytological determination of possible hereditary anomalies. This allows you to make a diagnosis in the early stages of pregnancy and decide whether to continue or terminate it.
With the help of these methods, the heredity and variability of somatic cells are studied, which compensates for the impossibility of applying hybridological analysis to a person. These methods, based on the reproduction of these cells in artificial conditions, analyze the genetic processes in individual cells of the body, and, due to the usefulness of the genetic material, use them to study the genetic patterns of the whole organism.
Hybrid cells containing 2 complete genomes, during division, usually “lose” chromosomes, preferably of one of the species. Thus, it is possible to obtain cells with the desired set of chromosomes, which makes it possible to study the linkage of genes and their localization in certain chromosomes.
Thanks to the methods of genetics of somatic cells, it is possible to study the mechanisms of the primary action and interaction of genes, the regulation of gene activity. The development of these methods has determined the possibility of accurate diagnosis of hereditary diseases in the prenatal period.
8.Simulation method
He studies human diseases on animals that can suffer from these diseases. It is based on Vavilov's law of homologous series of hereditary variability, for example, sex-linked hemophilia can be studied in dogs, epilepsy in rabbits, diabetes mellitus, muscular dystrophy in rats, cleft lip and palate in mice
Models in biology are used to model biological structures, functions and processes at different levels of organization of the living: molecular, subcellular, cellular, organ-systemic, organismic and population-biocenotic. It is also possible to model various biological phenomena, as well as the living conditions of individuals, populations and ecosystems.
In biology, three types of models are mainly used: biological, physico-chemical, and mathematical (logical-mathematical). Biological models reproduce certain conditions or diseases that occur in humans or animals in laboratory animals. This makes it possible to study in the experiment the mechanisms of the occurrence of a given condition or disease, its course and outcome, and to influence its course. Examples of such models are artificially induced genetic disorders, infectious processes, intoxications, reproduction of a hypertonic and hypoxic state, malignant neoplasms, hyperfunction or hypofunction of some organs, as well as neuroses and emotional states. used to create a biological model. various ways effects on the genetic apparatus, infection with microbes, the introduction of toxins, the removal of individual organs or the introduction of their metabolic products (for example, hormones), various effects on the central and peripheral nervous system, the exclusion of certain substances from food, placement in an artificially created habitat, and many other methods. Biological models are widely used in genetics, physiology, and pharmacology.
9.Immunogenetic
The immunological (serological) method includes the study of blood serum, as well as other biological substrates for the detection of antibodies and antigens.
There are serological reactions and immunological methods using physical and chemical labels. Serological reactions are based on the interaction of antibodies with antigens and registration of accompanying phenomena (agglutination, precipitation, lysis). In immunological methods, physical and chemical labels are used, which are included in the formed antigen-antibody complex, allowing the formation of this complex to be recorded.
Classical serodiagnosis is based on the determination of antibodies to an identified or suspected pathogen. A positive result of the reaction indicates the presence in the test blood serum of antibodies to the antigens of the pathogen, a negative result indicates the absence of such.
Serological reactions are semi-quantitative and allow to determine the antibody titer, i.e. the maximum dilution of the test serum, in which a positive result is still observed.
The detection of antibodies to the causative agent of a number of infectious diseases in the studied blood serum is not enough to make a diagnosis, since it may reflect the presence of post-infectious or post-vaccination immunity. That is why paired sera are examined - taken in the first days of the disease and after 7-10 days. In this case, the increase in antibody titer is assessed. A diagnostically significant increase in antibody titer in the studied blood serum relative to the initial level is 4 times or more. This phenomenon is called seroconversion.
In exotic infectious diseases, as well as in hepatitis, HIV infection and some other diseases, the very fact of detecting antibodies indicates that the patient is infected and has diagnostic value.
1. Genealogical method.
The method is based on tracing a trait in a number of generations, indicating family ties (compilation of a pedigree).
The collection of information starts from the proband.
Proband - a person whose pedigree needs to be compiled. Brothers and sisters of the proband are called sibs.
The method includes two steps:
1. Collection of information about the family.
2. Genealogical analysis.
Special characters are used to build a pedigree. Methods allow to establish the type of trait inheritance: autosomal dominant, autosomal recessive, sex-linked.
With autosomal dominant inheritance the gene appears in a heterozygous state in both sexes; immediately in the first generation; a large number of patients, both vertically and horizontally. Freckles, brachydactyly, cataracts, bone fragility, chondrodystrophic dwarfism, polydactyly are inherited according to this type.
With autosomal recessive inheritance the mutational gene appears only in the homozygous state in both sexes. As a rule, sick children are born to healthy parents (gene in a heterozygous state). The trait does not appear in every generation. This is how the following traits are inherited: Left-handedness, red hair, blue eyes, myopathy, diabetes mellitus, phenylketonuria.
With X-linked dominant inheritance people of both sexes are ill, it is more common in women. This is how the signs are inherited: pigmentary dermatosis, keratosis (loss of hairline), blistering of the feet, brown tooth enamel.
With an X-linked recessive inheritance mostly males are sick. In the family, half (50%) of the boys are sick, 50% of the girls are heterozygous for the mutant gene. This is how hemophilia A, Duchenne muscular dystrophy, and color blindness are inherited.
With Y-linked inheritance only men are sick. Such signs are called hollandic: syndactyly, hypertrichosis.
2. Cytogenetic method.
The method is based on microscopic examination of chromosomes, analysis of the human karyotype in normal and pathological conditions. The study of the chromosome set is carried out on metaphase plates of lymphocytes, fibroblasts cultivated under artificial conditions. Chromosome analysis is carried out by microscopy. To identify chromosomes, a morphometric analysis of the length of the chromosome and the ratio of their arms (centromeric index) are carried out, then karyotyping is carried out according to the Denver classification. This method allows you to establish the hereditary diseases of a person, and the structure of chromosomes, translocations, build genetic maps.
In 1969, T. Kasperson developed a method for differentiated staining of chromosomes, which made it possible to identify chromosomes by the nature of the distribution of stained segments. The heterogeneity of DNA in different regions along the length of the chromosome causes different staining of the segments (hetero- and euchromatic regions). This method makes it possible to detect aneuploidies, chromosomal rearrangements, translocations, polyploidies (trisomies on the 13th, 18th, 21st - autosomes; deletions). Deletions on the 5th chromosome form the "cat cry" syndrome; on the 18th - a violation of the formation of the skeleton and mental retardation.
If the violation concerns the sex chromosomes, then the method of studying the sex chromatin is used. Sex chromatin (Barr body) is a spiralized X chromosome, which is inactivated in the female body on the 16th day of embryonic development. The Barr body is disc-shaped and is found in interophase mammalian and human cell nuclei below the nuclear membrane. Sex chromatin can be determined in any tissue. Most often, epithelial cells of the buccal mucosa (buccal scraping) are examined.
In the karyotype of a normal female, there are two X chromosomes, and one of them forms the body of the sex chromatin. The number of sex chromatin bodies in humans and other mammals is one less than the number of X chromosomes in an individual. In a woman with the XO karyotype, the cell nuclei do not contain sex chromatin. With trisomy (XXX) - 2 bodies are formed, i.e. using sex chromatin to determine the number of sex chromosomes in blood smears; in the nuclei of neutrophilocytes, the bodies of sex chromatin look like drumsticks extending from the nucleus of leukocytes.
Normally, in women, chromatin - positive nuclei make up 20-40%, in men - 1-3%. Y-chromatin can also be detected in the buccal epithelium. It is an intensely luminous large chromocenter located at any point in the nucleus. Normally, in males, 20-90% of the nuclei contain Y-chromatin.
3. Population-statistical method.
The method allows to calculate the frequency of heterozygous carriage of a pathological gene in human populations. Distribution of gene and chromosomal abnormalities. The method uses demographic and statistical data, the mathematical processing of which is based on the Hardy-Weinberg law.
The study of the frequency of gene distribution is important for the analysis of the spread of human hereditary diseases. It is known that the vast majority of recessive alleles are presented in the heterozygous state. The Hardy-Weinberg law allows you to identify the frequency of carriage of a pathological gene. For example: the frequency of albinism encountered (aq 2) is 1:20000, i.e. q 2 aa = 1/20000, so q = √ 1/20000 = 1/141
p + q = 1, so p = 1- q = 1 1/141= 140/141; frequency of heterozygotes (albinism gene carriers) 2 pq Aa = 2 x140/141 x 1/141 = 1/70.
4. Twin method.
The method is based on the study of signs that change under the influence of living conditions in mono- and dizygotic twins. In genetic studies of twins, it is necessary to study both types comparatively. This is the only way to evaluate the influence of different environmental conditions on the same genotypes (in monozygotes), as well as the manifestation of different genotypes in the same environmental conditions (in dizygotes).
The similarity of signs in twins is called concordance, the differences in signs are called discordance. Comparison of the degree of similarity in two groups of twins makes it possible to judge the role of heredity and environment in pathological signs. The method is based on a comparative study of the characteristics of twins. It allows you to identify a list of diseases with a hereditary predisposition, to determine the role of the environment and heredity in the manifestation of the disease. To do this, use the coefficient of heredity (H) and the influence of the environment (E), which are calculated using the Holzinger formula:
H \u003d (% MZ -% DZ / 100 -% DZ) x 100
MZ - concordance of monozygotic twins, DZ - dizygotic twins.
If the value of H = 1, the sign is formed to a greater extent (100%) under the influence of hereditary factors; H = 0 - the sign is affected by the action of the environment (100%); H = 0.5 - the same degree of influence of the environment and heredity.
For example: the concordance of monozygotic twins in the incidence of schizophrenia is 70%, and that of dizygotic twins is 13%. Then H \u003d 70-13 / 100-13 \u003d 57/87 \u003d 0.65 (65%). Consequently, the predominance of heredity is 65%, and the environment is 35%.
The method is used to study:
1. The role of heredity and environment in the formation of the characteristics of the organism;
2. Specific factors that enhance or weaken the influence of the external environment;
3. Correlation of signs and functions;
5. Biochemical methods.
These methods are used to diagnose metabolic diseases caused by changes in the activity of certain enzymes (gene mutations). About 500 molecular diseases have been detected using these methods.
At various types diseases, it is possible to determine either the abnormal protein-enzyme itself, or the intermediate products of metabolism.
The methods include several steps:
1) Identification of simple, affordable methods (express methods), qualitative reactions of metabolic products in urine, blood.
2) Clarification of the diagnosis. For this, precise chromatographic methods for determining enzymes, amino acids, carbohydrates, etc. are used.
3) The use of microbiological tests based on the fact that some strains of bacteria can grow on media containing only certain amino acids, carbohydrates. If there is a substance required for a bacterium in the blood or urine, then active reproduction of bacteria is observed on such a prepared substrate, which does not happen in a healthy person.
Biochemical methods reveal hemoglobinopathies, metabolic disorders of amino acids (phenylkentonuria, alkaptonuria), carbohydrates (diabetes mellitus, galactosemia), lipids (amaurotic idiocy), copper (Konovalov-Wilson disease), iron (hemochromatosis), etc.
6. Method of dermatoglyphics.
Dermatoglyphics is a branch of genetics that studies the hereditary conditioned skin reliefs on the fingers, palms and soles of the feet. On these parts of the body there are epidermal protrusions - ridges that form complex patterns. Drawings of skin patterns are strictly individual and genetically determined. The process of formation of capillary relief occurs within 3-6 months of intrauterine development. The mechanism of ridge formation is associated with morphogenetic relationships between the epidermis and underlying tissues.
The genes that provide the formation of patterns on the fingertips are involved in the regulation of fluid saturation of the epidermis and dermis.
Gene A - causes the appearance of an arc on the digital pad, gene W - the appearance of a curl, gene L - the appearance of a loop. Thus, there are three main types of patterns on the fingertips (Fig. 5.5). The frequency of occurrence of patterns: arcs - in 6%, loops - about 60%, curls - 34%. A quantitative indicator of dermatoglyphics is the ridge count (the number of papillary lines between the delta and the center of the pattern; delta is the points of convergence of papillary lines forming a figure in the form of the Greek letter delta Δ).
On average, there are 15-20 ridges on one finger, on 10 fingers in men - 144.98; for women - 127.23 combs.
Palmar relief (palmoscopy) is more complex. It reveals a number of fields of pads and palmar lines. At the bases of II, III, IY, Y fingers there are finger triradii (a, c, d), at the base of the palm - palmar (t). The palmar angle - a t d normally does not exceed 57 0 (Fig. 5.6).
Skin patterns are hereditary. The ridge relief of the skin is inherited polygenically.
The formation of dermatoglyphic patterns can be influenced by some damaging factors in the early stages of embryogenesis (for example, the intrauterine effect of the rubella virus gives a deviation in patterns similar to Down's disease).
The dermatoglyphics method is used in clinical genetics as an additional confirmation of the diagnosis of chromosomal syndromes with a change in the karyotype.
7. Immunological methods.
The methods are based on the study of the antigenic composition of cells and body fluids - blood, saliva, gastric juice. The most commonly used antigens are erythrocytes, leukocytes, and blood proteins. Different types of erythrocyte antigens form systems of blood groups - AB0, Rh - factor. Knowledge of the characteristics of blood immunogenetics is necessary for blood transfusion.
8. Ontogenetic method.
The ontogenetic method makes it possible to study the regularities in the manifestation of signs in the process of development. The purpose of the method is early diagnosis and prevention of hereditary diseases. The method is based on biochemical, cytogenetic and immunological methods. In the early stages of postnatal ontogenesis, such diseases as phenylketonuria, galactosemia, Vitamin D-resistant rickets appear, the timely diagnosis of which contributes to preventive measures that reduce the pathology of diseases. Diseases such as diabetes mellitus, gout, alkaptonuria appear at later stages of ontogenesis. The method is of particular importance in studying the activity of genes that are in a heterozygous state, which makes it possible to identify recessive X-linked diseases. Heterozygous carriage is detected by examining the symptoms of the disease (with anophthalmia - a decrease in the eyeballs); with the help of stress tests (increased levels of phenylalanine in the blood in patients with phenylketonuria); using microscopic examination of blood cells of tissues (accumulation of glycogen in glycogenoses); by direct determination of gene activity.
9. Method of genetics of somatic cells.
Based on the study of hereditary material in clones of cells from tissues grown outside the body on nutrient media. In this case, it is possible to obtain pure genes, to obtain hybrid cells. This makes it possible to analyze the linkage of genes and their localization, the mechanisms of gene interaction, the regulation of gene activity, and gene mutations.
The use of anthropogenetics methods allows timely diagnosis of a hereditary disease.
Modern genetics studies the phenomena of heredity and variability, based on the achievements of various branches of biology - biochemistry, biophysics, cytology, embryology, microbiology, zoology, botany, plant growing and animal husbandry. Genetic research has greatly enriched the theoretical fields of biology, as well as zootechnics, veterinary medicine, breeding and breeding of farm animals, plant breeding and seed production, and medicine.
The main objects of genetic research at the molecular level are nucleic acid molecules - DNA and RNA, which ensure the preservation, transmission and implementation of hereditary information. The study of nucleic acids of viruses, bacteria, fungi, plant and animal cells cultivated outside the body (in vitro) makes it possible to establish the patterns of gene action during the life of the cell and organism.
The branch of genetics that studies the phenomena of heredity at the cellular level is called cytogenetics. A cell is an elementary system containing in full the genetic program of an individual's individual development. The main objects of research using cytological methods are plant and animal cells both in the body (in vivo) and outside the body, as well as viruses and bacteria. IN last years studies are carried out on somatic cells that multiply outside the body. Particular attention is paid to the study of chromosomes and some other cell organelles containing DNA - mitochondria, plastids, plasmids, as well as ribosomes, on which the synthesis of polypeptide chains - primary protein molecules is carried out.
The hybridological method was first developed and applied by G. Mendel in 1856-1863. to study the inheritance of traits and has since been the main method of genetic research. It includes a system of crossings of pre-selected parental individuals that differ in one, two or three alternative traits, the inheritance of which is being studied. important in the selection of plants and animals.It also includes the so-called recombination method, which is based on the phenomenon of crossing over - the exchange of identical sections in the chromatids of homologous chromosomes in prophase I of meiosis.This method is widely used for compiling genetic maps, as well as for creating recombinant molecules DNA containing the genetic systems of various organisms.
The monosomic method allows you to determine in which chromosome the corresponding genes are localized, and in combination with the recombination method, to determine the location of the genes in the chromosome.
The genealogical method is one of the variants of the hybridological method. It is used in the study of the inheritance of traits by analyzing pedigrees, taking into account their manifestation in animals of related groups in several generations. This method is used in the study of heredity in humans and animals, the infertility of which is species-specific.
The twin method is used to study the influence of certain environmental factors and their interaction with the genotype of an individual, as well as to identify the relative role of genotypic and modification variability in the overall variability of a trait. Twins are called offspring born in the same litter of singleton domestic animals (cattle, horses, etc.).
There are two types of twins - identical (identical), having the same genotype, and non-identical (fraternal), arising from separately fertilized two or more eggs.
The mutation method (mutagenesis) makes it possible to establish the nature of the influence of mutagenic factors on the genetic apparatus of the cell, DNA, chromosomes, and on changes in traits or properties. Mutagenesis is used in agricultural plant breeding, in microbiology to create new strains of bacteria. It has found application in silkworm breeding.
The population-statistical method is used to study the phenomena of heredity in populations. This method makes it possible to establish the frequency of dominant and recessive alleles that determine a particular trait, the frequency of dominant and recessive homozygotes and heterozygotes, the dynamics of the genetic structure of populations under the influence of mutations, isolation and selection. The method is the theoretical basis of modern animal breeding.
The phenogenetic method makes it possible to establish the degree of influence of genes and environmental conditions on the development of the studied properties and traits in ontogeny. A change in the feeding and maintenance of animals affects the nature of the manifestation of hereditarily determined traits and properties.
An integral part of each method is a statistical analysis - a biometric method. It is a series of mathematical techniques that allow you to determine the degree of reliability of the data obtained, to establish the likelihood of differences between the indicators of experimental and control groups of animals. An integral part of biometrics is the law of regression and the statistical law of heritability, established by F. Galton.
In genetics, computer modeling is widely used to study the inheritance of quantitative traits in populations, to evaluate breeding methods - mass selection, selection of animals according to breeding indices. This method has found especially wide application in the field of genetic engineering and molecular genetics.
For genetic research, a person is an inconvenient object, since in a person: experimental crossing is impossible; a large number of chromosomes; puberty comes late; a small number of descendants in each family; equalization of living conditions for offspring is impossible.
A number of research methods are used in human genetics.
genealogical method
The use of this method is possible in the case when direct relatives are known - the ancestors of the owner of the hereditary trait ( proband) on the maternal and paternal lines in a number of generations or the descendants of the proband also in several generations. When compiling pedigrees in genetics, a certain system of notation is used. After compiling the pedigree, its analysis is carried out in order to establish the nature of the inheritance of the trait under study.
Conventions adopted in the preparation of pedigrees:
1 - man; 2 - woman; 3 - gender not clear; 4 - the owner of the studied trait; 5 - heterozygous carrier of the studied recessive gene; 6 - marriage; 7 - marriage of a man with two women; 8 - related marriage; 9 - parents, children and the order of their birth; 10 - dizygotic twins; 11 - monozygotic twins.
Thanks to the genealogical method, the types of inheritance of many traits in humans have been determined. So, according to the autosomal dominant type, polydactyly (an increased number of fingers), the ability to roll the tongue into a tube, brachydactyly (short fingers due to the absence of two phalanges on the fingers), freckles, early baldness, fused fingers, cleft lip, cleft palate, cataracts of the eyes, fragility of bones and many others. Albinism, red hair, susceptibility to polio, diabetes mellitus, congenital deafness, and other traits are inherited as autosomal recessive.
The dominant trait is the ability to roll the tongue into a tube (1) and its recessive allele is the absence of this ability (2).
3 - pedigree for polydactyly (autosomal dominant inheritance).
A number of traits are inherited sex-linked: X-linked inheritance - hemophilia, color blindness; Y-linked - hypertrichosis of the edge of the auricle, webbed toes. There are a number of genes located in homologous regions of the X and Y chromosomes, such as general color blindness.
The use of the genealogical method showed that in a related marriage, compared with an unrelated one, the likelihood of deformities, stillbirths, and early mortality in the offspring increases significantly. In related marriages, recessive genes often go into a homozygous state, as a result, certain anomalies develop. An example of this is the inheritance of hemophilia in the royal houses of Europe.
- hemophilic; - carrier woman
twin method
1 - monozygotic twins; 2 - dizygotic twins.
Children born at the same time are called twins. They are monozygotic(identical) and dizygotic(variegated).
Monozygotic twins develop from one zygote (1), which is divided into two (or more) parts during the crushing stage. Therefore, such twins are genetically identical and always of the same sex. Monozygotic twins are characterized by a high degree of similarity ( concordance) in many ways.
Dizygotic twins develop from two or more eggs that are simultaneously ovulated and fertilized by different spermatozoa (2). Therefore, they have different genotypes and can be either the same or different sex. Unlike monozygotic twins, dizygotic twins are characterized by discordance - dissimilarity in many ways. Data on the concordance of twins for some signs are given in the table.
| signs | Concordance, % | |
|---|---|---|
| Monozygotic twins | dizygotic twins | |
| Normal | ||
| Blood group (AB0) | 100 | 46 |
| eye color | 99,5 | 28 |
| Hair color | 97 | 23 |
| Pathological | ||
| Clubfoot | 32 | 3 |
| "Hare Lip" | 33 | 5 |
| Bronchial asthma | 19 | 4,8 |
| Measles | 98 | 94 |
| Tuberculosis | 37 | 15 |
| Epilepsy | 67 | 3 |
| Schizophrenia | 70 | 13 |
As can be seen from the table, the degree of concordance of monozygotic twins for all the above characteristics is significantly higher than that of dizygotic twins, but it is not absolute. As a rule, the discordance of monozygotic twins occurs as a result of intrauterine development disorders of one of them or under the influence of the external environment, if it was different.
Thanks to the twin method, a person's hereditary predisposition to a number of diseases was clarified: schizophrenia, epilepsy, diabetes mellitus and others.
Observations on monozygotic twins provide material for elucidating the role of heredity and environment in the development of traits. Moreover, the external environment is understood not only as physical factors of the environment, but also as social conditions.
Cytogenetic method
Based on the study of human chromosomes in normal and pathological conditions. Normally, a human karyotype includes 46 chromosomes - 22 pairs of autosomes and two sex chromosomes. The use of this method made it possible to identify a group of diseases associated either with a change in the number of chromosomes or with changes in their structure. Such diseases are called chromosomal.
Blood lymphocytes are the most common material for karyotypic analysis. Blood is taken in adults from a vein, in newborns - from a finger, earlobe or heel. Lymphocytes are cultivated in a special nutrient medium, which, in particular, contains substances that “force” lymphocytes to intensively divide by mitosis. After some time, colchicine is added to the cell culture. Colchicine stops mitosis at the metaphase level. It is during metaphase that the chromosomes are most condensed. Next, the cells are transferred to glass slides, dried and stained with various dyes. Coloring can be a) routine (chromosomes stain evenly), b) differential (chromosomes acquire transverse striation, with each chromosome having an individual pattern). Routine staining allows you to identify genomic mutations, determine the group belonging of the chromosome, and find out in which group the number of chromosomes has changed. Differential staining allows you to identify chromosomal mutations, determine the chromosome to the number, find out the type of chromosomal mutation.
In cases where it is necessary to conduct a karyotypic analysis of the fetus, cells of the amniotic (amniotic) fluid are taken for cultivation - a mixture of fibroblast-like and epithelial cells.
Chromosomal diseases include: Klinefelter syndrome, Turner-Shereshevsky syndrome, Down syndrome, Patau syndrome, Edwards syndrome and others.
Patients with Klinefelter's syndrome (47, XXY) are always male. They are characterized by underdevelopment of the sex glands, degeneration of the seminiferous tubules, often mental retardation, high growth (due to disproportionately long legs).
Turner-Shereshevsky syndrome (45, X0) is observed in women. It manifests itself in slowing down puberty, underdevelopment of the gonads, amenorrhea (absence of menstruation), infertility. Women with Turner-Shereshevsky syndrome are small in stature, the body is disproportionate - the upper body is more developed, the shoulders are wide, the pelvis is narrow - the lower limbs are shortened, the neck is short with folds, the “Mongoloid” eye shape and a number of other signs.
Down syndrome is one of the most common chromosomal diseases. It develops as a result of trisomy on chromosome 21 (47; 21, 21, 21). The disease is easily diagnosed, as it has a number of characteristic features: shortened limbs, a small skull, a flat, wide nose, narrow palpebral fissures with an oblique incision, the presence of a fold of the upper eyelid, and mental retardation. Violations of the structure of internal organs are often observed.
Chromosomal diseases also occur as a result of changes in the chromosomes themselves. Yes, deletion R-arm of autosome number 5 leads to the development of the "cat's cry" syndrome. In children with this syndrome, the structure of the larynx is disturbed, and in early childhood they have a kind of “meowing” voice timbre. In addition, there is a retardation of psychomotor development and dementia.
Most often, chromosomal diseases are the result of mutations that have occurred in the germ cells of one of the parents.
Biochemical method
Allows you to detect metabolic disorders caused by changes in genes and, as a result, changes in the activity of various enzymes. Hereditary metabolic diseases are divided into diseases of carbohydrate metabolism (diabetes mellitus), metabolism of amino acids, lipids, minerals, etc.
Phenylketonuria refers to diseases of amino acid metabolism. The conversion of the essential amino acid phenylalanine to tyrosine is blocked, while phenylalanine is converted to phenylpyruvic acid, which is excreted in the urine. The disease leads to the rapid development of dementia in children. Early diagnosis and diet can stop the development of the disease.
Population-statistical method
It is a method of studying the distribution of hereditary traits (inherited diseases) in populations. An essential point when using this method is the statistical processing of the obtained data. Under population understand the totality of individuals of the same species, living in a certain territory for a long time, freely interbreeding with each other, having a common origin, a certain genetic structure and, to one degree or another, isolated from other such populations of individuals of a given species. A population is not only a form of existence of a species, but also a unit of evolution, since the basis of microevolutionary processes culminating in the formation of a species are genetic transformations in populations.
The study of the genetic structure of populations deals with a special section of genetics - population genetics. In humans, three types of populations are distinguished: 1) panmictic, 2) demes, 3) isolates, which differ from each other in number, frequency of intra-group marriages, the proportion of immigrants, and population growth. The population of a large city corresponds to the panmictic population. The genetic characteristics of any population includes the following indicators: 1) gene pool(the totality of genotypes of all individuals of a population), 2) gene frequencies, 3) genotype frequencies, 4) phenotype frequencies, marriage system, 5) factors that change gene frequencies.
To determine the frequencies of occurrence of certain genes and genotypes, hardy-weinberg law.
Hardy-Weinberg law
In an ideal population, from generation to generation, a strictly defined ratio of frequencies of dominant and recessive genes (1), as well as the ratio of frequencies of genotypic classes of individuals (2) is preserved.
p + q = 1, (1)R 2 + 2pq + q 2 = 1, (2)
Where p— frequency of occurrence of the dominant gene A; q- the frequency of occurrence of the recessive gene a; R 2 - the frequency of occurrence of homozygotes for the dominant AA; 2 pq- frequency of occurrence of Aa heterozygotes; q 2 - the frequency of occurrence of homozygotes for the recessive aa.
The ideal population is a sufficiently large, panmictic (panmixia - free crossing) population, in which there is no mutation process, natural selection and other factors that disturb the balance of genes. It is clear that ideal populations do not exist in nature; in real populations, the Hardy-Weinberg law is used with amendments.
The Hardy-Weinberg law, in particular, is used to roughly count the carriers of recessive genes for hereditary diseases. For example, phenylketonuria is known to occur at a rate of 1:10,000 in a given population. Phenylketonuria is inherited in an autosomal recessive manner, therefore, patients with phenylketonuria have the aa genotype, that is q 2 = 0.0001. From here: q = 0,01; p= 1 - 0.01 = 0.99. Carriers of the recessive gene have the Aa genotype, that is, they are heterozygotes. The frequency of occurrence of heterozygotes (2 pq) is 2 0.99 0.01 ≈ 0.02. Conclusion: in this population, about 2% of the population are carriers of the phenylketonuria gene. At the same time, you can calculate the frequency of occurrence of homozygotes for the dominant (AA): p 2 = 0.992, just under 98%.
A change in the balance of genotypes and alleles in a panmictic population occurs under the influence of constantly acting factors, which include: the mutation process, population waves, isolation, natural selection, gene drift, emigration, immigration, inbreeding. It is thanks to these phenomena that an elementary evolutionary phenomenon arises - a change in the genetic composition of a population, which is the initial stage in the process of speciation.
Human genetics is one of the most intensively developing branches of science. It is the theoretical basis of medicine, reveals the biological basis of hereditary diseases. Knowing the genetic nature of diseases allows you to make an accurate diagnosis in time and carry out the necessary treatment.
Go to lectures №21"Variability"
The main method of genetics - hybridological(crossing of certain organisms and analysis of their offspring, this method was used by G. Mendel).
The hybridological method is not suitable for a person for moral and ethical reasons, as well as because of the small number of children and late puberty. Therefore, indirect methods are used to study human genetics.
1) Genealogical- study of pedigrees. Allows you to determine the patterns of inheritance of traits, for example:
- if a trait appears in each generation, then it is dominant (right-handedness)
- if after a generation - recessive (blue eyes)
- if more often manifested in one sex, this is a sex-linked trait (hemophilia, color blindness)
2) Gemini- comparison of identical twins, allows you to study modification variability (determine the impact of the genotype and environment on the development of the child).
Identical twins are obtained when one embryo at the stage of 30-60 cells divides into 2 parts, and each part grows into a child. Such twins are always of the same sex, they are very similar to each other (because they have exactly the same genotype). The differences that occur in such twins during life are associated with exposure to environmental conditions.
Fraternal twins (not studied in the twin method) are obtained when two eggs are fertilized simultaneously in the mother's genital tract. Such twins can be of the same or different sex, similar to each other like ordinary brothers and sisters.
3) Cytogenetic- study under a microscope of a chromosome set - the number of chromosomes, features of their structure. Allows detection of chromosomal diseases. For example, Down syndrome has one extra 21st chromosome.
4) Biochemical- studying chemical composition organism. Allows you to find out if patients are heterozygous for a pathological gene. For example, heterozygotes for the phenylketonuria gene do not get sick, but an increased content of phenylalanine can be detected in their blood.
5) Population genetic- study of the proportion of different genes in the population. Based on the Hardy-Weinberg law. Allows you to calculate the frequency of normal and pathological phenotypes.
Choose one, the most correct option. What method is used to reveal the influence of the genotype and environment on the development of the child
1) genealogical
2) twin
3) cytogenetic
4) hybridological
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. The twin research method is used
1) cytologists
2) zoologists
3) genetics
4) breeders
5) biochemists
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. Geneticists, using the genealogical method of research, make up
1) genetic map of chromosomes
2) crossover scheme
3) family tree
4) the scheme of ancestral parents and their family ties in a number of generations
5) variation curve
Answer
1. Choose two correct answers from five and write down the numbers under which they are indicated. The genealogical research method is used to establish
1) the dominant nature of the inheritance of the trait
2) the sequence of stages of individual development
3) causes of chromosomal mutations
4) type of higher nervous activity
5) linkage of a trait with sex
Answer
2. Choose two correct answers out of five and write down the numbers under which they are indicated in the table. The genealogical method allows you to determine
1) the degree of influence of the environment on the formation of the phenotype
2) the influence of education on human ontogenesis
3) type of trait inheritance
4) the intensity of the mutation process
5) stages of evolution of the organic world
Answer
3. Choose two correct answers out of five and write down the numbers under which they are indicated in the table. The genealogical method is used to determine
3) patterns of inheritance of traits
4) number of mutations
5) the hereditary nature of the trait
Answer
4. Choose two correct answers from five and write down the numbers under which they are indicated. The genealogical method is used to
1) studying the influence of upbringing on human ontogenesis
2) obtaining gene and genomic mutations
3) studying the stages of evolution of the organic world
4) detection of hereditary diseases in the family
5) studies of human heredity and variability
Answer
5. Choose two correct answers from five and write down the numbers under which they are indicated. The genealogical method is used to determine
1) the degree of influence of environmental factors on the formation of a trait
2) the nature of the inheritance of the trait
3) the probability of transferring a trait in generations
4) structures of chromosomes and karyotype
5) the frequency of occurrence of a pathological gene in a population
Answer
Choose one, the most correct option. The main method for studying the patterns of inheritance of traits
1) genealogical
2) cytogenetic
3) hybridological
4) twin
Answer
Choose one, the most correct option. To determine the nature of the influence of the genotype on the formation of the phenotype in humans, the nature of the manifestation of signs is analyzed.
1) in the same family
2) in large populations
3) in identical twins
4) in fraternal twins
Answer
Establish a correspondence between the characteristic and the method: 1) cytogenetic, 2) genealogical. Write the numbers 1 and 2 in the correct order.
A) researching family pedigree
B) the adhesion of the trait to the floor is revealed
C) the number of chromosomes is studied at the stage of metaphase of mitosis
D) a dominant trait is established
D) the presence of genomic mutations is determined
Answer
Choose one, the most correct option. A method that allows you to study the influence of environmental conditions on the development of traits
1) hybridological
2) cytogenetic
3) genealogical
4) twin
Answer
Choose one, the most correct option. What method of genetics is used to determine the role of environmental factors in the formation of the human phenotype
1) genealogical
2) biochemical
3) paleontological
4) twin
Answer
Choose one, the most correct option. What method is used in genetics to study genomic mutations
1) twin
2) genealogical
3) biochemical
4) cytogenetic
Answer
1. Choose two correct answers from five and write down the numbers under which they are indicated. The cytogenetic method is used to determine
1) the degree of influence of the environment on the formation of the phenotype
2) inheritance of sex-linked traits
3) karyotype of the organism
4) chromosomal abnormalities
5) the possibility of manifestation of signs in descendants
Answer
2. Choose two correct answers out of five and write down the numbers under which they are indicated. The cytogenetic method allows to study in humans
1) hereditary diseases associated with genomic mutations
2) development of signs in twins
3) features of the metabolism of his body
4) its chromosome set
5) the pedigree of his family
Answer
3. Choose two correct answers from five and write down the numbers under which they are indicated. Cytogenetic method for studying human genetics
1) based on the compilation of human genealogies
2) used to study the characteristic inheritance of a trait
3) consists in microscopic examination of the structure of chromosomes and their number
4) used to detect chromosomal and genomic mutations
5) helps to establish the degree of influence of the environment on the development of traits
Answer
All of the following research methods, except for two, are used to study the heredity and variability of a person. Identify these two methods that "fall out" from the general list, and write down the numbers under which they are indicated.
1) genealogically
2) hybridological
3) cytogenetic
4) experimental
5) biochemical
Answer
Choose from the text three sentences that give a true description of the methods of studying human genetics and heredity. Write down the numbers under which they are indicated. (1) The genealogical method used in human genetics is based on the study of a family tree. (2) Thanks to the genealogical method, the nature of the inheritance of specific traits was established. (3) The twin method predicts the birth of identical twins. (4) When using the cytogenetic method, the inheritance of human blood groups is determined. (5) The inheritance pattern of hemophilia (poor blood clotting) was established by pedigree analysis as an X-linked recessive gene. (6) The hybridological method makes it possible to study the spread of diseases in the natural zones of the Earth.
Answer
The following is a list of genetic methods. All of them, except for two, relate to the methods of human genetics. Find two terms that "fall out" of the general series, and write down the numbers under which they are indicated.
1) twin
2) genealogical
3) cytogenetic
4) hybridological
5) individual selection
Answer
1. Choose two correct answers from five and write down the numbers under which they are indicated. The biochemical research method is used for:
1) studying the karyotype of the organism
2) establishing the nature of the inheritance of the trait
3) diagnosing diabetes
4) detection of enzyme defects
5) determination of the mass and density of cell organelles
Answer
2. Choose two correct answers out of five and write down the numbers under which they are indicated. The biochemical research method is used for
1) determining the degree of influence of the environment on the development of signs
2) study of metabolism
3) studying the karyotype of the organism
4) studies of chromosomal and genomic mutations
5) clarification of diagnoses of diabetes mellitus or phenylketonuria
Answer
1. Choose three options. The essence of the hybridological method is
1) crossing individuals that differ in several ways
2) studying the nature of inheritance of alternative traits
3) using genetic maps
4) application of mass selection
5) quantitative accounting of phenotypic traits of offspring
6) selection of parents according to the rate of reaction of signs
Answer
2. Choose two correct answers. The features of the hybrid method include
1) selection of parent pairs with alternative features
2) the presence of chromosomal rearrangements
3) quantitative accounting of the inheritance of each trait
4) identification of mutant genes
5) determination of the number of chromosomes in somatic cells
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. What methods of scientific research are used to diagnose diabetes mellitus and determine the nature of its inheritance?
1) biochemical
2) cytogenetic
3) twin
4) genealogical
5) historical
Answer
Choose two correct answers out of five and write down the numbers under which they are indicated in the table. Methods used in human genetics
1) cytogenetic
2) genealogical
3) individual selection
4) hybridological
5) polyploidization
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. To study human hereditary diseases, amniotic fluid cells are examined using methods
1) cytogenetic
2) biochemical
3) hybridological
4) physiological
5) comparative anatomical
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. The population-statistical method of studying human genetics is used to
1) calculation of the frequency of occurrence of normal and pathological genes
2) study of biochemical reactions and metabolism
3) predicting the likelihood of genetic abnormalities
4) determining the degree of influence of the environment on the development of traits
5) studying the structure of genes, their number and location in the DNA molecule
Answer
Establish a correspondence between examples and methods for detecting mutations: 1) biochemical, 2) cytogenetic. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) loss of the X chromosome
B) the formation of meaningless triplets
C) the appearance of an extra chromosome
D) a change in the structure of DNA within a gene
E) change in chromosome morphology
E) change in the number of chromosomes in the karyotype
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. The twin method for studying human genetics is used to
1) studying the nature of the inheritance of a trait
2) determining the degree of influence of the environment on the development of traits
3) predicting the probability of having twins
4) assessment of genetic predisposition to various diseases
5) calculation of the frequency of occurrence of normal and pathological genes
Answer
Choose two correct answers from five and write down the numbers under which they are indicated. Used in genetics
1) convergent similarity of individuals
2) hybridological analysis
3) crossing individuals
4) artificial mutagenesis
5) centrifugation
Answer
Analyze the table "Methods for studying human heredity." For each cell marked with a letter, select the appropriate term from the list provided.
1) establishing the nature of inheritance of various traits
2) microscopic examination of the number and structure of chromosomes
3) biochemical method
4) cytogenetic method
5) twin method
6) the study of family ties between people
7) study of the chemical composition of blood
8) detection of metabolic disorders
Answer
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