Basic symbols:

When constructing pedigrees, it is necessary to observe following rules :

a) it is necessary to find out the number of generations from the collected history;

b) the pedigree begins to be built from the proband;

c) each generation is numbered with Roman numerals on the left;

d) symbols indicating individuals of one generation are located on a horizontal line and numbered in Arabic numerals.

There are the following types of inheritance signs:

autosomal dominant;

autosomal recessive;

X-linked (sex-linked) dominant;

X-linked (sex-linked) recessive;

holandric.

Autosomal dominant type of inheritance

A sick child is born to sick parents with a 100% probability if they are homozygous; 75% if they are heterozygous.

Autosomal recessive mode of inheritance

Both men and women are affected equally.

The probability of having a sick child from healthy parents is 25% if they are heterozygous, 0% if both of them or one of them is homozygous for the dominant gene.

Often manifests itself in consanguineous marriages.

X-linked (sex-linked) dominant type of inheritance

Sick people occur in every generation.

Women are more affected.

If a father is sick, then all his daughters are sick.

A sick child is born to sick parents with a probability of 100% if the mother is homozygous, 75% if the mother is heterozygous.

The probability of having a sick child from healthy parents is 0%.

X-linked (sex-linked) recessive mode of inheritance

Patients do not occur in every generation.

Mostly men are affected.

The probability of having a sick boy born to healthy parents is 25%, and a sick girl is 0%.

Hollandic type of inheritance

Sick people occur in every generation.

Only men get sick.

If a father is sick, then all his sons are sick.

The probability of having a sick boy from a sick father is 100%.

Twin method (proposed in 1876 by F. Galton) is the study of genetic patterns in twins.

The essence of the method: comparison of characteristics in different groups of twins based on their similarities (concordance) or differences (discordance).

Method steps:

1. Compiling a sample of twins from the entire population.

2. Diagnosis of zygosity of twins.

3. Establishing the relative role of heredity and environment in the formation of a trait.

D
To assess the role of heredity and environment in the formation and development of a trait, they use Holzinger's formula:

where N is the proportion of hereditary factors, KMB% and KDB% concordance of monozygotic and dizygotic twins as a percentage.

If H is greater than 0.5, then the genotype plays a large role in the formation of the trait; if H is less than 0.5, then the environment plays a large role.

Cytogenetic method - This is the study of a karyotype using microscopic technology.

Method steps:

1. Obtaining and culturing cells (lymphocytes, fibroblasts) on artificial nutrient media.

2. Addition of phytohemagglutinin to the nutrient medium to stimulate cell division.

3. Stopping cell division at the metaphase stage by adding colchicine.

4. Treatment of cells with a hypotonic NaCl solution, as a result of which the cell membrane is destroyed and a “scattering” of chromosomes is obtained.

5. Staining of chromosomes with specific dyes.

6. Microscoping and photographing chromosomes.

7. Drawing up an idiogram and its analysis.

The method allows:

a) diagnose genomic and chromosomal mutations;

b) determine the genetic sex of the organism.

Population statistical method - is the study of the genetic composition of a population. It is based on the Hardy-Weinberg law and allows us to determine the frequency of genes and genotypes in different populations (see section VII).

Biochemical methods. The cause of most hereditary monogenic diseases are metabolic defects associated with enzymopathies (disturbances in the structure of enzymes involved in metabolic reactions). At the same time, intermediate metabolic products accumulate in the body, and therefore, by determining them or the activity of enzymes, using biochemical methods it is possible to diagnose hereditary metabolic diseases (gene mutations). Quantitative biochemical methods (stress tests) make it possible to identify heterozygous carriage of a pathological recessive gene.

Recombinant DNA Methods(DNA cloning and nucleic acid hybridization)- allow you to detect a pathological gene in the genome if this gene is sequenced (the nucleotide sequence is completely determined).

Dermatoglyphic analysis is the study of human ridge skin (skin of the fingertips, palmar side of the hands and plantar side of the feet), where the papillary layer of the dermis is strongly pronounced.

The method is applied:

a) to establish the zygosity of twins;

b) as an express method for diagnosing the congenital component of some hereditary diseases.

Typically, with genomic pathology, a combination of certain indicators is noted: radial loops on the 4th and 5th fingers, four-digit groove, main palmar angle from 60 0 to 80 0, etc.

Chemical methods based on high-quality color chemical reactions. They are used for preliminary diagnosis of hereditary metabolic diseases. As a screening test diagnosis of phenylketonuria The method of wetting strips of paper soaked in a 10% solution of FeCl 3 or 2,4 dinitrophenylhydrazine with the child’s urine is used. If phenylpyruvic acid is present in the urine, a greenish color appears on the filter paper.

Definition of X- andY-sex chromatin. Buccal epithelial cells or leukocytes are used for research. X-chromatin is determined by staining the preparation acetorcein, and Y-chromatin - when stained Acrychinipriet. These methods make it possible to identify the number of sex chromosomes in a karyotype (the number of X chromosomes is always one more than the number of X-chromatin clumps, the number of Y chromosomes is equal to the number of Y-chromatin clumps); establish the genetic sex of an individual, diagnose chromosomal diseases of sex (in combination with other methods).

Prenatal diagnostic methods make it possible to identify hereditary defects of the fetus in the early stages of pregnancy.

1. Indirect methods (the object of the study is a pregnant woman).

2. Direct methods ( the object of study is the fetus).

Indirect methods are indicated for all pregnant women and include:

obstetric and gynecological examination;

medical genetic examination;

serological examination;

study of the content of embryo-specific proteins.

Level - AF is increased with: threatened miscarriage; intrauterine fetal death; Rh incompatibility between mother and fetus; multiple pregnancy; umbilical cord hernia; neural tube defects; sacrococcygeal teratoma. Low level -FP observed in Down syndrome.

Direct research methods: non-invasive (ultrasonography) andinvasive (amniocentesis, chorionic villus biopsy, fetoscopy).

Direct non-invasive methods are indicated to all pregnant women women (safe for mother and fetus).

Ultrasonography - the use of ultrasound to obtain an image of the fetus and its membranes on a monitor. The method is used at 12–15 weeks of pregnancy, when all organ systems of the fetus are formed, and makes it possible to identify multiple pregnancies and major defects (hydrocephalus, anencephaly, aplasia of the limbs, etc.).

Direct invasive methods are carried out according to strict indications (woman’s age is more than 35 years; structural rearrangements of chromosomes in one of the parents; the first child has a disease with a recessive type of inheritance; pregnancy due to psychological trauma, serious illness, etc.).

Amniocentesis. After treating the skin, the abdominal wall and uterus are pierced with a needle, and amniotic fluid is extracted with a syringe under the control of ultrasonography. The liquid is used for biochemical research (diagnosis of gene mutations), and the fetal cells contained in it are used for cytogenetic research (diagnosis of chromosomal and genomic mutations).

Chorionic villus biopsy performed under ultrasonography control at 8–12 weeks of pregnancy. Using a catheter with a plastic cannula connected to a syringe, 10–25 mg of chorionic villi are extracted and used for cytogenetic, biochemical studies and DNA analysis. Method allows you to diagnose various mutations in early pregnancy.

Fetoscopy (amnioscopy) carried out at 18–22 weeks of pregnancy using a fiberoptic endoscope inserted under local anesthesia into the amnion cavity through the abdominal wall of the uterus. The method allows examine the fetus, placenta, umbilical cord and take fetal blood from the umbilical cord to diagnose hereditary blood diseases. Rarely used; in 5–10% of cases it can cause miscarriage.

The number of various diseases that can significantly limit human life and even lead to death is constantly growing. At the same time, it is worth understanding an important fact: some of the pathologies that disrupt the functions of the body are not acquired, but, as they say, are rooted in genetics. We are talking about the inheritance of autosomal traits that are passed on from generation to generation.

What is meant by an autosomal trait?

Delving into the essence of this term, it is important first of all to pay attention to such a property of any living creature as heredity. In most cases, children are similar to their parents, but at the same time, certain differences are almost always noticeable among representatives of the same family.

In other words, everyone has their own individual characteristics, but they are actually part of the genetic heritage. Thus, an autosomal trait is nothing more than the inheritance of the genetic characteristics of the parents.

Disease transmission

In addition to specific individual characteristics, a person can inherit some diseases from his father and mother. This fact is due to the influence of mutations of genes that are localized in autosomes. Moreover, such traits can be divided into two key areas: dominant and recessive. Both have a significant impact on the structure of a particular person's heritage.

Autosomal dominant trait

Each type of inheritance has its own characteristics. If we consider autosomal dominant, then it is worth noting that in this case, in order to obtain it, transmission of the mutant allele of either parent is sufficient. This trait of inheritance can occur equally in both men and women. Essentially, autosomal dominant inheritance can be defined as the transmission of a trait that is controlled by the dominant allele of an autosomal gene. With this type of inheritance, one mutant allele localized in the autosome will be sufficient for the manifestation of the disease.

The good news is that most diseases that are transmitted in this way do not cause significant harm to health, nor do they have a significant detrimental effect on human reproductive functions. If we compare the level of influence on the percentage of diseases, then dominant traits more often become the cause of any deviations than recessive ones. If one of the spouses has such a mutation and the other is in full health, the risk of transmitting the disease is 50%. For this reason, an autosomal dominant trait, manifested in the form of a mutation, can be transmitted from generation to generation and thus have a familial character. Unlike autosomal recessive traits, these traits appear in heterozygotes, which have one mutant and one normal allele on homologous chromosomes.

Diseases with autosomal dominant inheritance

With this type of transmission of hereditary characteristics, a heterozygous carrier of the mutation is sufficient for the disease to manifest in the next generation. An interesting fact is that a dominant autosomal trait implies the same frequency of diseases in both girls and boys.

If the disease resulting from exposure of this type transmission of heredity, is present in the child, while both parents are healthy, this fact means the occurrence of a new mutation in the germ cells of the mother or father. It is important to understand that in one family the impact of a dominant gene on the condition of children may differ. This means that clinical picture and the severity of the diseases will not necessarily be the same.

Examples of diseases

The autosomal trait of the dominant type is clearly manifested through a disease such as Marfan syndrome. Such a diagnosis means that the connective tissue in the human body is damaged. Patients suffering from Marfan syndrome typically have thin, thin fingers, and the length of the limbs is disproportionate. Such people often develop defects of the aorta and heart valves.

Another hereditary disease, which is determined by the presence of autosomal dominant inheritance traits, is brachydactyly, also known as short-fingeredness. This is a fairly rare symptom that occurs in one of the parents. The manifestation of this disease is noticeable already in the first time after birth due to unnatural changes in the phalanges of the toes and hands.

Hereditary deafness is an autosomal trait that can also be defined as dominant.

Amyotrophic lateral sclerosis (ALS, or Charcot's disease) is also a consequence of an autosomal dominant inheritance trait and belongs to the group of motor neuronal diseases. This disease can be defined as a fatal, progressive, neurodegenerative disorder that was caused by the degeneration of cells of the central nervous system- motor neurons. The main function of these cells is to maintain muscle tone and ensure motor coordination.

Autosomal recessive trait: features

This type of inheritance has several key characteristics:

• may not affect the condition of children even if there were many carriers of a hereditary disease in the pedigree, since recessive traits do not appear in every generation (horizontal inheritance, in contrast to dominant traits);
• a recessive mutant gene (a) manifests itself phenoptically only when it is in a homozygous state (aa);
• hereditary disease manifests itself equally often in both females and males;
• the likelihood that a born child will be sick increases significantly in the case of consanguineous marriages;
• Phenoptically healthy parents of a child with manifest disease may be heterozygous carriers of the mutant gene.

It is worth noting that among all hereditary pathologies, recessive autosomal inheritance of traits is the most common. Diseases that can be identified as a consequence of this symptom include a large group of fermentopathies leading to metabolic disorders, diseases of the blood (including homeostasis), kidneys, immune system, etc.

Examples of autosomal recessive diseases

• This group of symptoms includes (glycogenosis). The manifestation of this genetic disorder is caused by a deficiency of the enzyme glucose-6-photosphatase, which leads to a significant deterioration in the liver’s ability to reproduce glucose. Violation is so important process inevitably leads to hypoglycemia.
• - This is also an autosomal trait that can be defined as recessive. This disease has another name - leucinosis. This diagnosis implies a metabolic disorder resulting from improper metabolism of branched-chain amino acids. This disease can be classified as organic acidemia.
• Tay-Sachs disease, which also has names such as early childhood amaurotic idiocy and hexosaminidase deficiency. This disease is genetic, autosomal recessive and leads to a progressive deterioration of the child's physical and mental abilities.
• It is worth noting that, unlike a disease such as deafness, the autosomal trait of color blindness is recessive, but it can be classified as “sex-linked”. can be either partial or complete. The most common is a distorted perception of the color red. It is worth noting that in some cases, impaired perception of a particular color is compensated by better discrimination of shades of other colors.

• Phenylketonuria is an autosomal recessive trait that implies an inherited metabolic disease. This disorder is caused by a deficiency of the enzyme phenylalanine.

What is meant by sex-linked diseases?

Diseases in this group are caused by the fact that men have one X chromosome, and women have two. Accordingly, a male representative, having inherited a pathological gene, is hemizygous, and a female is heterozygous. Hereditary traits that are transmitted in an X-linked manner can occur with different probabilities in both sexes.

If we consider dominant diseases, it is worth noting that such cases are more common in women. This is explained by the increased possibility of receiving a pathological allele from one of the parents. As for men, they are able to inherit a gene of this type only from their mother. Moreover, in the male line, the dominant autosomal trait linked to the X chromosome is transmitted to all daughters, while in sons the disease does not manifest itself, since they do not receive the father’s chromosome.

If you pay attention to the autosomal recessive X-linked trait of inheritance, you will notice that such diseases develop predominantly in hemizygous men. In turn, women are virtually always heterozygous and, therefore, phenoptically healthy. X-linked hereditary traits include diseases such as hemophilia, Hunter syndrome and others.

As for Y-linked inheritance, these characteristics are due to the presence of the Y chromosome exclusively in men. The action of such a gene can only be transmitted from father to son over many generations.

Features of the mitochondrial method of inheritance

This type of inheritance stands out among others in that the transmission of traits occurs through mitochondria located in the plasma of the egg. Moreover, the ring chromosome is located in each mitochondria, and there are approximately 25,000 of them in the egg. Gene mutations in mitochondria appear when progressive ophthalmoplegia, mitochondrial myopathies and Leberaf are present in the body. Diseases that are a consequence of the action of this factor can be transmitted from mothers equally often to both daughters and sons.

In general, both autosomal unlinked traits and other types of hereditary mutations can have a significant impact on physical condition several generations and are the cause of many serious diseases.

The gene is autosomal G., localized on any chromosome, with the exception of the sex chromosomes.

Large medical dictionary. 2000 .

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Autosomal dominant inheritance (Gr. autos- himself and soma- body; lat. dominare- dominate, dominate) - inheritance of a trait controlled by the dominant allele of an autosomal gene; a type of inheritance in which one mutant allele located on an autosome is sufficient for a trait or disease to manifest itself.

Autosomal dominant traits, in contrast to autosomal recessive traits, appear in heterozygotes who have one mutant and one normal allele on homologous chromosomes.

Since a single mutant gene is sufficient to produce the phenotypic manifestations of an autosomal dominant disease, these conditions arise in many patients as a result of a new mutation. The more severe the disease, the greater the incidence of cases resulting from de novo gene mutations. In severe diseases, decreased reproductive function limits the transmission of the mutant gene from generation to generation. In some cases, the emergence of a new mutation has been noted old age parents (over 40 years old).

Genes that are part of 22 pairs of non-sex chromosomes are called autosomal. Autosomal dominant diseases are diseases in which one mutant gene (allele) in a heterozygous state is sufficient for the appearance of phenotypic manifestations.

Autosomal dominant inheritance of diseases is characterized by a number of the following signs, which are detected in most cases:

• the disease is transmitted vertically along the pedigree, and cases of the disease are diagnosed in each generation;
• the risk of inheriting the disease for any of the patient's children is 50%;
• phenotypically normal family members do not inherit diseases to their offspring;
• both sexes are affected with equal frequency;
• a significant proportion of cases of the disease are caused by a new mutation.

With autosomal dominant inheritance, in contrast to the X-linked type, transmission of the disease through the male line is possible. Since a man passes on a Y rather than an X chromosome to his sons, in cases where a hereditary disease is passed from father to son, X-linked inheritance is excluded.

With autosomal dominant inheritance, there is significant variability in clinical manifestations within a family. In most cases, this is due to variable expression of the mutant gene. The exact cause of this variability is unknown, but it is most likely that it is due to the influence of modifier genes and environmental factors on the phenotype. In some families, obligate carriers of the mutant gene do not have phenotypic manifestations of the disease. This phenomenon of autosomal dominant inheritance is called incomplete penetrance, i.e. inheritance follows the “all or nothing” principle. In some cases, when there is an impression of a lack of penetrance, the patient may have a low degree of somatic mosaicism or germline cell mosaicism for this gene. Somatic mosaicism occurs at the stage of embryonic development due to a mutation in a somatic cell, leading to the formation of mixed genotypes in fetal cells, some of which contain the mutation, while others lack it. Typically, in these patients, the effects of the mutant gene are less pronounced or absent. Germline cell mosaicism occurs in the embryo after conception and is limited to cells that are the precursors of eggs or sperm. It is often observed in conditions such as osteogenesis imperfecta and syndromes associated with craniostenosis (Apert and Crouzon syndromes).

Since a single mutant gene is sufficient for the phenotypic manifestations of autosomal dominant inheritance, these conditions arise in many patients as a result of a new mutation. The more severe the disease, the greater the incidence of cases arising from de novo gene mutations. In severe diseases, decreased reproductive function limits the transmission of the mutant gene. In some cases of the occurrence of a new mutation, the parents are elderly (over 40 years old).

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