The cytogenetic method is used to determine the degree of influence. medical biology
Human heredity is difficult to study:
Approximately the same life expectancy of the researcher (doctor) and the patient, as much as possible can study 3-4 generations in the family,
Late onset human puberty and a small number of offspring,
A large number of chromosomes and genes,
Lack of recorded pedigrees in the family,
The hybridological method cannot be used.
There are a number of methods that allow you to trace the inheritance of traits. This allows you to establish a diagnosis, fight diseases, consult people who need it.
Clinical and genealogical
Biochemical
cytogenetic
Gemini
population-statistical
Immune-genetic
twin method.
MZ (OB) identical.
1 egg + 1 sperm → zygote, which further divides into 2 embryos in the early stages.
Always the same sex (genetically identical). The differences between them depend mainly on the action of external factors.
2 egg + 2 sperm = → 2 zygotes.
DZ (RB). They are similar to each other like 2 sisters or 2 brothers born separately. They can also be heterosexual or same-sex. Differences depend on heredity and environmental factors.
The method makes it possible to distinguish between the role of heredity and environment in the diversity of human traits.
If the occurrence of a trait (or its absence) is largely dependent on the genetic construct, then coincidence is observed more often in OB.
The intra-pair similarity of twins (similarity) is called concordance, in OB it is > than RB.
(psoriasis MH 61% RB 13%). Schizophrenia 69% (10%). Depression (psychosis) 96% (19%).
90-100% skin tone, nose shape, iris tone, OB
Blood type, saliva, Rhesus in OB - 100%
81-90% fingerprint. Pattern at OB.
The essence of the method: the study of the intra-pair similarity of twins, by comparing which one can judge the influence of the environment and heredity on the development of a particular trait (impact of chemical agents, drugs ...).
cytogenetic method.
This microscopic analysis of chromosomes (karyotype) allows you to identify numerical and structural changes in chromosomes (rearrangements, breakdowns, etc..
Chromosomes are studied in dividing cells of the bone marrow, blood lymphocytes, less often skin, muscles.
Chromosomes can also be studied in the unborn child (embryo): chorionic villi, placental cells, cord blood, amniotic fluid (amniotic fluid - amniocentesis method).
Cells are selected, grown on a nutrient medium, colchitin is added. It stops mitosis at the metaphase stage. Micropreparations must be stained. There are various methods of cytogenetic diagnostics. The method can determine the sex chromatin (Barr body)
Indications for the method:
In the proband, his parents or relatives with suspected chromosomal disease (clarification of the diagnosis)
For severe mental disorders
With primary amenorrhea (absence of menstruation) infertility
Spontaneous abortion, stillbirth
In children with multiple malformations that are not suitable for any disease.
When studying the mutagenic effect, any factors (drugs, drugs, radiation ...)
When conducting medical genetic counseling.
The method leads to more accurate diagnosis, timely treatment and prevention of the birth of a sick child.
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- the study of the chemical composition of the body. 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) the pedigree of the family is being investigated
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
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
© D.V. Pozdnyakov, 2009-2019
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" incision of the eyes 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. Thus, deletion of the p-arm of autosome No. 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.
42. Prenatal diagnosis of congenital and hereditary diseases is a complex branch of medicine that is developing rapidly. She uses and ultrasound diagnostics (ultrasound), and operational equipment (chorion biopsy, amnio- and cordocentesis, biopsy of muscles and skin of the fetus), and laboratory methods (cytogenetic, biochemical, molecular genetic).
Prenatal diagnosis is extremely important in medical genetic counseling, since it allows you to move from probable to unambiguous prediction of a child's health in families with genetic complications. Currently, prenatal diagnosis is carried out in the I and II trimesters of pregnancy, that is, during periods when, if a pathology is detected, it is still possible to terminate the pregnancy. Today, it is possible to diagnose almost all chromosomal syndromes and about 100 hereditary diseases, in which a biochemical defect has been reliably established.
Prenatal diagnosis- complex prenatal diagnostics in order to detect pathology at the stage of intrauterine development. Allows you to detect more than 98% of fetuses with Down syndrome (trisomy 21); trisomy 18 (known as Edwards syndrome) about 99.9%; trisomy 13 (Patau syndrome) about 99.9%, more than 40% of cardiac developmental disorders, etc. If the fetus has a disease, parents, with the help of a consultant doctor, carefully weigh the possibilities of modern medicine and their own in terms of the rehabilitation of the child. As a result family decides on the fate of this child and decides on the continuation of gestation or termination of pregnancy.
Prenatal diagnosis also includes determining paternity in early pregnancy, as well as determining the sex of the fetus.
Indications for prenatal diagnosis: the presence of a hereditary disease in the family; mother's age over 37; carriage by the mother of the gene for an X-linked recessive disease; the presence in the past of spontaneous abortions in early pregnancy, stillbirths, children with malformations, chromosomal pathology; the presence of structural rearrangements of chromosomes in one of the parents; heterozygosity of both parents for one pair of alleles in pathology with an autosomal recessive type of inheritance; zone of increased background radiation.
Currently, indirect and direct methods of prenatal diagnosis are used. With indirect methods, a pregnant woman is examined (obstetric and gynecological methods, blood serum for alpha-fetoprotein), with direct methods - the fetus.
Direct methods that take place without tissue damage, without surgical intervention, include ultrasonography. To the direct method, which take place with a violation of the integrity of the tissues - chorionbiopsy, amniocentesis, cordocentesis and fetoscopy.
Ultrasonography, echography- This is the use of ultrasound to obtain an image of the fetus and its membranes, the state of the placenta.
At the 5th week of pregnancy, it is already possible to obtain an image of the membranes of the embryo, by the end of the 6th week it is possible to register its cardiac activity, and at the 7th week it is possible to obtain an image of the unborn child itself.
In the first two months of pregnancy, ultrasound does not yet reveal abnormalities in the development of the fetus, but it can determine its viability. At the 12th - 20th week of pregnancy, it is already possible to diagnose a twin pregnancy, localization of the placenta, absence of the brain or spinal cord, defects in the skeletal system, closure of the neural tube, infection of the natural channels of the gastrointestinal tract.
The method is safe, so the duration of the study is not limited, and it can be used repeatedly. In the normal course of pregnancy, a double ultrasound is performed, and in pregnancy with a risk of complications, it is performed at intervals of 2 weeks.
Ultrasound of the fetus is mandatory for: the presence of congenital malformations in parents and close relatives; extragenital diseases in a pregnant woman, for example, hypertension, diabetes mellitus, thyrotoxicosis, heart disease, obesity, etc.; the presence of stillborn children, perinatal death of two or more children; the threat of abortion, bleeding; insufficient weight gain of the pregnant woman; discrepancy between the size of the uterus and the gestational age; multiple pregnancy; fibromyoma of the uterus.
In general, ultrasound allows you to obtain data on the size of the fetus (length of the body, hip, shoulder, head diameter), on the presence of dysmorphia, on the work of the heart, on the volume of fluid in the embryonic membrane and the size of the placenta.
Ultrasound can detect some malformations in the fetus. For example, the absence of the brain and spinal cord, an excessive amount of cerebrospinal fluid in the cranial cavity, anomalies in the structure of the kidneys, abnormal development of the limbs, lungs, multiple congenital malformations, heart defects, edema of the fetus and placenta.
Echography of the placenta allows you to establish its location, the presence of detachment of its individual sections, cysts, signs of aging, thinning or thickening of the placenta.
Doppler ultrasound, color Doppler reflect fetal circulation.
NMR imaging of the fetus allows to detect structural anomalies that are not detected by ultrasound, for example, small anomalies of the brain, tuberous sclerosis, anomalies in the structure of the kidneys, etc.
Three research methods are often used: the level of alpha-fetoprotein (a special embryonic protein), the content of chorionic gonadotropin (a hormone produced by the placenta during pregnancy) and free estriol (female sex hormone) in the blood of a woman in the 2nd trimester of pregnancy. Deviations of these indicators from the norm serve as indicators of high risk for the fetus.
The content of alpha-fetoprotein in biological fluids is increased with multiple fetal malformations, spinal hernia, excessive amount of cerebrospinal fluid in the skull, absence of the brain or spinal cord, malformations of the gastrointestinal tract, defects in the anterior abdominal wall, kidney anomalies, fetoplacental insufficiency (insufficient work of the placenta), fetal growth retardation, multiple pregnancy, preeclampsia, Rhesus conflict, viral hepatitis B.
The concentration of alpha-fetoprotein in the blood of a pregnant woman is reduced in cases of chromosomal diseases in the fetus, for example, Down's disease, or if the pregnant woman has type I diabetes mellitus.
Currently, the study of alpha-fetoprotein is carried out in the 1st trimester of pregnancy simultaneously with the determination of protein A specific for pregnant women, which makes it possible to diagnose Down's disease and some other chromosomal abnormalities in the fetus already at 11-13 weeks.
Chorionic gonadotropin (CG) is determined already on the 8th - 9th day after conception. When examining a woman's blood in the 2nd trimester of pregnancy, an increase in the level of hCG indicates a delay in intrauterine development of the fetus, a high risk of its death, placental abruption, and other types of placental insufficiency (disruption of the placenta).
Study of pregnancy protein I (Schwangerschaft protein I) in the blood plasma of women already in the 1st trimester of pregnancy is an indicator of fetal chromosomal diseases.
Chorionic biopsy- this is the taking of chorion tissue (embryonic membrane). It is carried out between the 8th and 10th weeks. The fabric is used for cytogenetic and biochemical studies, DNA analysis. Using this method, all types of mutations (gene, chromosomal and genomic) can be detected.
A significant advantage of chorionbiopsy is that it can be used in the early stages of fetal development. That is, if deviations in the development of the fetus are revealed and the parents decide to terminate the pregnancy, then an abortion at 10–12 weeks is less dangerous than at 18–20 weeks, when the results of amniocentesis become known.
Amniocentesis- obtaining amniotic fluid (fluid around the fetus) and fetal cells for analysis. Material can be obtained at the 16th week of pregnancy.
The main indications for amniocentesis are general: the age of the pregnant woman is more than 35 years; abnormal levels of alpha-fetoprotein, human chorionic gonadotropin and free estriol in the blood of the pregnant woman; the presence of several serious risk factors for pregnancy complications.
Separate: stillbirths, perinatal mortality; the birth of a previous child with chromosomal diseases or with dysmorphic signs; chromosomal balanced mosaicism in parents; fragile X syndrome in the next of kin; determining the sex of the fetus at risk of hereditary X-linked diseases (hemophilia, immunodeficiency, etc.). ); hereditary metabolic diseases; the impact of teratogenic agents on the body of a pregnant woman during critical periods of fetal development; intrauterine growth retardation and fetal dysmorphia according to ultrasound; the risk of intrauterine infections (rubella, cytomegaly, toxoplasmosis).
Complications with this method of research do not exceed 1%.
Amniotic fluid is used for biochemical studies that detect gene mutations. And the cells are used for DNA analysis (detects gene mutations), cytogenetic analysis and detection of X- and Y-chromatin (diagnoses genomic and chromosomal mutations).
Biochemical studies of amniotic fluid can provide valuable information. For example, the diagnosis of adrenogenital syndrome (impaired synthesis of hormones by the adrenal cortex and the functioning of the hypothalamus-pituitary-ovaries system) in an embryo is possible as early as the 8th week.
The study of the spectrum of amino acids in the amniotic fluid allows you to identify some hereditary metabolic diseases in the fetus, for example, arginine-succinic aciduria, citrullinuria, etc.
The study of amniotic fluid is used to detect chromosomal abnormalities, determine the activity of enzymes.
Cordocentesis- taking blood from the umbilical cord. The material is used for cytogenetic, molecular genetic and biochemical studies. Held from the 18th to the 22nd week.
The advantage of cordocentesis compared to amniocentesis is that fetal blood is taken, which is critical for diagnosing intrauterine infections, such as HIV, rubella, cytomegaly, parvovirus B19.
However, indications for cordocentesis are limited due to the high risk of complications, such as intrauterine fetal death (up to 6%), miscarriage (9%).
Fetoscopy- examination of the fetus with a fiberoptic endoscope inserted into the embryonic membrane through the anterior wall of the uterus. The method allows you to examine the fetus, umbilical cord, placenta and perform a biopsy.
Fetoscopy has a very limited use, because it is accompanied by a high risk of miscarriage and is technically difficult.
Modern technologies make it possible to biopsy skin, muscles, liver of the fetus. The material is used to diagnose severe hereditary diseases, such as genodermatosis, muscular dystrophy, glycogenosis, etc.
The risk of abortion when using methods of prenatal diagnosis that violate the integrity of tissues is 1 - 2%.
Vesicocentesis- a puncture of the bladder wall of the fetus to obtain its urine. The material is used for research in cases of serious diseases and malformations of the organs of the urinary system.
Pre-implantation diagnosis of hereditary diseases made possible by the advent of in vitro fertilization and the use of multiple copies of embryonic DNA.
There is technology to detect diseases such as Tay-Sachs, hemophilia, Duchenne myodystrophy, fragile X-chromosome, etc. However, it is available to a few very large centers and is expensive.
Methods are being developed to isolate fetal cells circulating in the blood of a pregnant woman for cytogenetic, molecular genetic and immunological analyses.
The development and dissemination of methods for prenatal diagnosis of hereditary diseases will significantly reduce the frequency of hereditary pathology in newborns.
BIOLOGICAL BASES OF LIFE HUMAN
Cytogenetic method, its significance
Cytogenetic analysis allows recording the diagnosis of a hereditary disease in the form of a karyotypic formula.
The cytogenetic method (method of chromosome analysis) is based on a microscopic examination of the structure and number of chromosomes. It was widely used in the 20s of the XX century, when the first information about the number of chromosomes in humans was obtained. In the 1930s, the first 10 pairs of chromosomes were identified.
In 1956, Swedish scientists J. Tiyo and A. Levan proved for the first time that a person has 46 chromosomes.
The cytogenetic method is used for:
The study of karyotypes of organisms;
Clarification of the number of chromosome sets, the number and morphology of chromosomes for the diagnosis of chromosomal diseases;
Mapping chromosomes;
To study the genomic and chromosomal mutation process;
Study of chromosomal polymorphism in human populations.
The human chromosome set contains a large number of chromosomes, basic information about which can be obtained by studying them in the metaphase of mitosis and prophase - the metaphase of meiosis. human cells for direct chromosome analysis is obtained by bone marrow puncture and gonadal biopsy, or indirectly method - by culturing peripheral blood cells (lymphocytes), when a significant amount of metaphases are obtained. The indirect method also examines cells of the amniotic fluid or fibroblasts obtained during amniocentesis or chorion biopsy, cells of abortuses, stillborns, etc.
More often, chromosomes are examined in peripheral heparinized blood lymphocytes. Phytohemagglutinin is added to stimulate mitosis, and colchicine is added to stop mitosis. The preparation is stained with nuclear dyes: 2% acetorsein solution, azureosin, Unna dye, Giemsa solution, etc. Cover with a cover slip, remove excess dye with filter paper, examine under a microscope with oil immersion.
Recently, all studies in human cytogenetics are carried out using differential staining of chromosomes, which make it possible to distinguish each chromosome pair. There are several ways to color: Q, G, C, R (Fig. 1.42). In solving the problems of diagnosing chromosomal diseases, different methods of differential staining are used in combination. Due to the differential coloration of chromosomes, minor chromosomal breakdowns can be detected: small deletions, translocation, etc.
Having received a micropreparation, they study it visually and make up a karyotype idiogram, that is, the ordered placement of each pair of chromosomes according to individual differences: the total length of the chromosome, shape, location of the centromere.
Most of the chromosomes can only be assigned to certain groups according to the Denver classification by this method (see section 1.2.2.12).
This method allows diagnosing many hereditary diseases, studying the mutation process, complex rearrangements and the slightest chromosomal abnormalities in cells that have entered the division phase and beyond division.
Patients with multiple congenital malformations, children with delayed physical and psychomotor development, patients with undifferentiated forms of oligophrenia (dementia), with impaired sexual differentiation, women with menstrual irregularities (primary or secondary amenorrhea), families with infertility, women with habitual miscarriage (miscarriage, stillbirth).
Cytogenetics is an independent branch of the study of heredity, which studies various, primarily observable (explicated) carriers that contain information about genetic heredity. Such carriers are chromosomes of various types (polytene, mitotic and meiotic), plastids, interphase nuclei, and, to a lesser extent, mitochondria.
Proceeding from this, the cytogenetic method is a set of methods and technologies for studying, first of all, chromosomes, during which their quantitative parameter is established, their chemical and biological description is made, the structure and modes of behavior during cell division are studied. The scientific task of this study is to establish a relationship between the nature and dynamics of changes in the structure of chromosomes and a picture that reflects the variability of characters.
One of the most important areas of research, which involves the cytogenetic method, is the analysis of the human karyotype. This study, as a rule, is carried out on cultures in which the division of germ and somatic cells occurs.
The most common culture for this kind of research is peripheral blood cells such as lymphocytes, fibroblasts, and bone marrow cells. The most accessible culture used in medical cytogenetics is blood lymphocytes. The reason for this is that, as a rule, they are the subject of analysis and in the fetus, the cytogenetic method involves the use of cell cultures, the choice of which is determined by a number of factors. The main one is the gestational age. For example, at this period of less than 12 weeks, it is best to perform a cytogenetic analysis of chromosomes with the participation of chorion cells, and at gestation periods of more than 12 weeks, it is advisable to consider the cells of the fetus itself for research. For this purpose, they are specially isolated from the placenta and fetal blood.
To establish a karyotype, cytogenetic heredity requires obtaining a blood sample in an amount of at least 1-2 ml. At the same time, the method itself involves conducting a study consisting of three main stages:
Isolation and on which the analysis will be carried out;
The color of the drug;
Carrying out a thorough analysis of the drug under a microscope.
The cytogenetic method of genetics can be effective only when the following conditions are met. First, there must be a certain number of cells in the metaphase stage. Secondly, the cultivation must be carried out in strict accordance with the established rules and for a period of at least 72 hours. Thirdly, fixation of cells should be carried out with a solution and methanol in a strict ratio of these substances 3: 1.
At the stage of coloring the preparation for the choice of colors is made taking into account the very purpose of the study, that is, what type of rearrangements need to be studied. Most often, the method of continuous staining is used, since it is the simplest for determining the quantitative parameter of chromosomes. Modern research most of all uses this staining method to determine karyotype abnormalities in their quantitative expression. But such a cytogenetic method does not make it possible to determine and reveal the structural dynamics of chromosomes. Therefore, other, special methods are used that allow leveling this disadvantage of the continuous staining method. The most common of them, such as the method of differentiated coloring, G-method, R-method and others.
And, finally, the third stage of the study consists in the microscopic study of stained chromosomes that are in the metaphase stage. In the course of it, the number of normal and abnormal cells of the human fetal body is established. For this, as a rule, analysis of several tissues is carried out.