Loss of the middle part of the chromosome. The loss of a section of a chromosome is called. Less common chromosomal abnormalities

All hereditary diseases are caused by mutations—defects in the genetic material.

Chromosomal diseases- diseases caused by chromosomal and genomic and

Changes that cause diseases:

• loss of a section of a chromosome;
• adding new sections or even entire chromosomes

As we know, there are non-sex chromosomes - .

let's consider autosomal(chromosomal) diseases - those that are inherited and do not depend on gender

Deletions- chromosomal rearrangements, in which a section of a chromosome is lost. The deletion may be due to a chromosome break or the result of unequal crossing over.

1. There is a common one deletion of chromosome 5

(cry-cat syndrome)

The disease is quite rare, its symptoms are:

• developmental delay;
• muscular dystrophy;
• cat-like face (set eyes);
• a violation in the structure of the larynx, so the child produces a cry similar to a cat’s meow (hence the name)

2. Deletion 3rd chromosome

Such organisms are not viable.

It turns out that rearrangement or loss of even one small section of a chromosome leads to quite significant complications.

Deletion 21st chromosome

(bleeding, leukemia, anemia)

This chromosomal disease is characterized by the fact that either few red blood cells are produced or they are shaped like a sickle (sickle cell anemia). Because red blood cells are responsible for transporting oxygen, the disease is severe.

3. Trisomy on chromosome 21

(Down syndrome)

The karyotype of such an organism contains not two, but three 21 chromosomes.

This is a very common chromosomal disorder. Birth frequency is 1: 500 (0.2%).

Symptoms:

1) Mongoloid type of face;

2) shortened limbs;

3) mental retardation (many scientists argue with this statement. People with Down syndrome have rather “different” mental activity than most normal people);

Causes of trisomy:

Typically, each human cell contains 23 pairs of different chromosomes. Each chromosome carries genes that are necessary for the proper development and maintenance of our body. Conceptually, a person inherits 23 chromosomes from the mother (via the egg) and 23 chromosomes from the father (via the sperm). However, sometimes a person inherits an additional chromosome set from one of the parents. In the case of Down syndrome, it is most often inherited two copies of chromosome 21 from mother and one 21st chromosome from the father, for a total of three chromosomes 21. It is because of this type of inheritance that Down syndrome is called trisomy 21.

There are several more chromosomal diseases (trisomies), but we will not discuss them in detail...

Sex chromosome mutations

1. Trisomy X

An organism with this disease has XXX instead of two Xs. Morphological and functional disorders are associated mainly with the reproductive system. People with this mutation may not even be aware of their karyotype.

(There are also tetrasomy - XXXX, and pentasomy, but developmental deviations in these cases are already serious)

2. Monosomy X

(Turner syndrome)

There are deviations in both mental and physical (mainly sexual) development.

3. XXY or XYU syndrome

(Kleintelfer syndrome)

XXY - manifests itself as an effeminate physique (secondary sexual characteristics) in men. People with such a chromosomal disease are mentally healthy, but infertile.

XYY - healthy, can have offspring, but aggressive (socially dangerous).

These are not all mutations known to science and medicine. Many of them lead to death at the embryonic stage. Therefore, unlike gene diseases, chromosomal diseases less likely to be inherited.

Yesterday, my husband and I watched one of the episodes of the series “The Female Doctor,” where there was a story about a mother carrying twins, where the boy was suspected of having Down syndrome. My husband began to question me in detail - where does this come from and why do chromosomal diseases occur in children if their parents are completely healthy and there are no problems in the family?

The question is correct, serious and very complex, it is difficult to answer, because medicine, alas, does not fully know why breakdown occurs in chromosomes. But the problem is existing, real, and many women are very worried during pregnancy when the doctor tells them to undergo a screening test for such tests. Let's talk about this in detail.

Why do they occur and how does it happen?

Breakdowns of genes and chromosomes are serious disorders of the body, since genes are responsible for the development of the body, its full functioning and various types of diseases. Back in school, you studied the basics of genetics and have a general idea of ​​what happens inside cells. The nucleus of each cell in the body contains information about its life program and functions. Densely packed into 46 chromosomes. All body cells have a double (even set of chromosomes), but sex cells have a half set.

That is, a human egg or sperm has only 23 chromosomes. Therefore, from mom and dad, each person receives half the set of chromosomes and, accordingly, characteristics. That's why we look like both parents. But not all of the genes on these chromosomes work; some of them come into operation immediately, others as they grow and develop, others at the stage of aging, etc. Which genes and which sections of chromosomes received from parents will be working and non-working - only Mother Nature can predict this, we cannot know this, at least for now...

Sometimes breakdowns occur in the chromosome set, there may be defects at the level of one gene, at the level of a group of genes - then more often it is not developmental defects that occur, but hereditary diseases and syndromes, for example, phenylketonuria. Sometimes entire sections of chromosomes may suffer (the so-called chromosome arms), which can break off, change their place, etc.
Loss or duplication of some chromosomes in one of the pairs may occur, and a person is born with a different set of chromosomes - most often this is trisomy (instead of two chromosomes, three) in one of the pairs of chromosomes, as for example in Down syndrome (trisomy of 21 pairs of chromosomes), Edwards syndrome (18 pairs of chromosomes) or Patau syndrome (13 pairs of chromosomes).

This can occur as a result of disruption of the division process and decreased control over it by the body. That is, as a result of cell division (whether it is a germ cell or an embryo cell). All chromosomes in a pair are tied in the middle by a kind of bridge or rope; during division, this bridge or rope must unravel and the halves of the chromosome must disperse to different poles of the cell. Then the body will add a similar mirror copy to each half - then cell division will be equivalent.

If, as a result of division, the bridge is not untied, then two pieces of chromosome will go to one cell, and none to the other. Then in one cell there will be one extra chromosome - and in the other it will be missing. Cells with an incomplete set of chromosomes are usually not viable and die, but cells with an additional set survive quite well. If a woman produces an egg with such an additional set, then when fertilized, she can give birth to a child with a chromosomal abnormality. While the body is young, it quite tightly and clearly controls the process of formation of such cells, although control is still not one hundred percent, but as you age, control decreases. Therefore, doctors talk about an increased risk of having a child with hereditary and chromosomal abnormalities as a woman (and a man too) gets older.

Incorrect unequal cell division can be influenced by various environmental factors and the internal state of the body. Thus, when women and men work in hazardous production conditions, the risks increase, as do those who live in poor environmental conditions, often get sick, have a family history of hereditary diseases, etc. Unfortunately, it is impossible for a man to know the condition of his eggs and sperm in terms of genetic abnormalities. Only one out of every 400 eggs in a lifetime may be formed with a defect, or one out of a billion defective sperm may be formed. It is impossible to calculate this. But the risk factor in the form of age is a reality, but not a death sentence!

Types of chromosomal syndromes.

I won’t bore you with long lectures on genetics and molecular technologies; let’s outline possible anomalies in general terms that may arise. In total, more than two hundred chromosomal syndromes and anomalies are known, given that a person has 23 pairs of chromosomes in each of them. Including sex chromosomes, various types of abnormalities are possible. Options can be different - complete or incomplete (partial trisomy), chromosome deletion, monosomy of a chromosome pair, mosaic translocation, gene defects, etc. Each type is more or less favorable in terms of prognosis for life and health.

The most prognostically favorable syndrome in terms of chromosomal abnormalities are the so-called balanced translocations - this is the exchange of sections of similar chromosomes with each other. In such people, the appearance and functioning of the body are no different from an ordinary person; the features of their genetics can only be revealed through special research. But such people have a sharply increased rate of having a child with genetic disorders. Since they themselves are carriers of pathological chromosomes. For such parents, the risk of having babies with anomalies increases to 50%, from 5% under normal conditions.

Another variant of chromosomal disorders is mosaic trisomy or chromosome deletions. This is the presence of such cells not in all organs and tissues, and the more tissues with defects, the worse the prognosis for life and health, in terms of the formation of developmental defects. The most severe variants are complete trisomies (one pair of three chromosomes in all cells) or monosomy (one pair of only one chromosome in all cells). With such defects, most pregnancies end in termination of pregnancy in the early stages due to the triggering of the mechanism of natural selection by nature.

If the fetus develops before 20-22 weeks, severe pregnancy pathologies often occur with miscarriage, threats of miscarriage, increased uterine tone, premature aging of the placenta, hypoxia and toxicosis. There may also be options for the development of pregnancy before term, and then the prognosis for the child will depend on the severity of certain abnormalities; on average, the life expectancy of people with chromosomal pathology is about 30 years. The state of health and level of intelligence of such people depends on the degree and depth of the damage; many of the children live and develop quite normally and can take care of themselves. They do quite feasible work and communicate with their peers. It is very difficult to say during pregnancy how problematic the unborn child will be; much depends on the level of damage to the genetic material.

How to conduct research?

Many future parents ask the question: is it possible to find out in advance in the early stages whether the child has chromosomal pathologies and which ones? Today, medicine is making attempts to detect such disorders early, so that parents, together with doctors, can decide whether to continue the development of pregnancy or whether it is better to terminate it. There is a certain set of criteria by which one can suspect (but not with one hundred percent probability determine) the presence of genetic and chromosomal diseases. These include the threat of miscarriage in the early stages and later, throughout pregnancy, constant nagging pain in the abdomen. This is a nonspecific symptom. The threat of termination of pregnancy also occurs with an absolutely normal fetus; there are a lot of factors for its occurrence; this fact alone is not at all sufficient for suspicion.

The following indicators may be additional reasons for suspicion:

An increase in the thickness of the cervical fold in the fetus according to ultrasound data at 12 weeks of pregnancy,
- low motor activity of the fetus and insufficient movements,
- low levels of alpha-fetoproterin and PAPP-A, against the background of increased levels of human chorionic gonadotropin at 12-14 weeks of pregnancy,
- a lag in the growth of bones from 20-22 weeks and an increase in the fetal renal pelvis from the same period,
- underdevelopment and early aging of the placenta,
- signs of fetal hypoxia, unsatisfactory data on Dopplerometry and CTG.
- manifestations of polyhydramnios or oligohydramnios.

However, all these signs are not one hundred percent proof that there is a problem with the child; this can only be known for sure by carrying out invasive research methods. This is a biopsy of the chorionic villus (placenta), as well as an analysis of amniotic fluid and umbilical cord blood sampling for examination and identification of the fetal genotype.
Tomorrow we will talk about examination for suspected Down syndrome, as the most common chromosome defect.

Methods for diagnosing Down syndrome during pregnancy.

Chromosomal mutations (otherwise called aberrations, rearrangements) are unpredictable changes in the structure of chromosomes. They are most often caused by problems that occur during cell division. Exposure to initiating environmental factors is another possible cause of chromosomal mutations. Let's figure out what manifestations of this kind of changes in the structure of chromosomes can be and what consequences they have for the cell and the entire organism.

Mutations. General provisions

In biology, a mutation is defined as a permanent change in the structure of genetic material. What does "persistent" mean? It is inherited by the descendants of an organism that has mutant DNA. This happens as follows. One cell receives the wrong DNA. It divides, and two daughters copy its structure completely, that is, they also contain altered genetic material. Then there are more and more such cells, and if the organism proceeds to reproduction, its descendants receive a similar mutant genotype.

Mutations usually do not pass without leaving a trace. Some of them change the body so much that the result of these changes is death. Some of them force the body to function in a new way, reducing its ability to adapt and leading to serious pathologies. And a very small number of mutations benefit the body, thereby increasing its ability to adapt to environmental conditions.

Mutations are divided into gene, chromosomal and genomic. This classification is based on differences occurring in different structures of genetic material. Chromosomal mutations, thus, affect the structure of chromosomes, gene mutations affect the sequence of nucleotides in genes, and genomic mutations make changes to the genome of the whole organism, adding or subtracting a whole set of chromosomes.

Let's talk about chromosomal mutations in more detail.

What types of chromosomal rearrangements can occur?

Depending on how the changes are localized, the following types of chromosomal mutations are distinguished.

1. Intrachromosomal - transformation of genetic material within one chromosome.
2. Interchromosomal - rearrangements, as a result of which two non-homologous chromosomes exchange their sections. Non-homologous chromosomes contain different genes and do not occur during meiosis.

Each of these types of aberrations corresponds to certain types of chromosomal mutations.

Deletions

Deletion is the separation or loss of any part of a chromosome. It is easy to guess that this type of mutation is intrachromosomal.

If the outermost part of a chromosome is separated, the deletion is called terminal. If genetic material is lost closer to the center of the chromosome, such a deletion is called interstitial.

This type of mutation can affect the viability of the organism. For example, the loss of a section of a chromosome encoding a certain gene provides a person with immunity to the immunodeficiency virus. This adaptive mutation arose approximately 2,000 years ago, and some people with AIDS managed to survive only because they were lucky enough to have chromosomes with an altered structure.

Duplications

Another type of intrachromosomal mutation is duplication. This is the copying of a section of a chromosome, which occurs as a result of an error during the so-called crossover, or crossing over, during cell division.

A section copied in this way can maintain its position, rotate 180°, or even be repeated several times, and then such a mutation is called amplification.

In plants, the amount of genetic material can increase precisely through repeated duplications. In this case, the ability of an entire species to adapt usually changes, which means that such mutations are of great evolutionary significance.

Inversions

Also refers to intrachromosomal mutations. Inversion is a rotation of a certain section of a chromosome by 180°.

The part of the chromosome turned over as a result of inversion can be on one side of the centromere (paracentric inversion) or on opposite sides of it (pericentric). The centromere is the so-called region of the primary constriction of the chromosome.

Typically, inversions do not affect the external signs of the body and do not lead to pathologies. There is, however, an assumption that in women with an inversion of a certain part of chromosome nine, the likelihood of miscarriage during pregnancy increases by 30%.

Translocations

Translocation is the movement of a section of one chromosome to another. These mutations are of the interchromosomal type. There are two types of translocations.

1. Reciprocal is the exchange of two chromosomes in certain areas.
2. Robertsonian - fusion of two chromosomes with a short arm (acrocentric). During the Robertsonian translocation, short sections of both chromosomes are lost.

Reciprocal translocations lead to problems with childbearing in humans. Sometimes such mutations cause miscarriage or lead to the birth of children with congenital developmental pathologies.

Robertsonian translocations are quite common in humans. In particular, if a translocation occurs involving chromosome 21, the fetus develops Down syndrome, one of the most frequently reported congenital pathologies.

Isochromosomes

Isochromosomes are chromosomes that have lost one arm, but have replaced it with an exact copy of their other arm. That is, in essence, such a process can be considered deletion and inversion in one bottle. In very rare cases, such chromosomes have two centromeres.

Isochromosomes are present in the genotype of women suffering from Shereshevsky-Turner syndrome.

All types of chromosomal mutations described above are inherent in various living organisms, including humans. How do they manifest themselves?

Chromosomal mutations. Examples

Mutations can occur in sex chromosomes and in autosomes (all other paired chromosomes of the cell). If mutagenesis affects sex chromosomes, the consequences for the body are usually severe. Congenital pathologies arise that affect the mental development of the individual and are usually expressed in changes in the phenotype. That is, outwardly mutant organisms differ from normal ones.

Genomic and chromosomal mutations occur more frequently in plants. However, they are found in both animals and humans. Chromosomal mutations, examples of which we will consider below, manifest themselves in the occurrence of severe hereditary pathologies. These are Wolf-Hirschhorn syndrome, “cry the cat” syndrome, partial trisomy disease on the short arm of chromosome 9, as well as some others.

Cry of the cat syndrome

This disease was discovered in 1963. It occurs due to partial monosomy on the short arm of chromosome 5, caused by a deletion. One in 45,000 children is born with this syndrome.

Why did this disease get such a name? Children suffering from this disease have a characteristic cry that resembles a cat's meow.

When the short arm of the fifth chromosome is deleted, different parts of it may be lost. The clinical manifestations of the disease directly depend on which genes were lost during this mutation.

The structure of the larynx changes in all patients, which means that “cat cry” is characteristic of everyone without exception. Most people suffering from this syndrome experience a change in the structure of the skull: a decrease in the brain region, a moon-shaped face. In case of “cry the cat” syndrome, the ears are usually located low. Sometimes patients have congenital pathologies of the heart or other organs. Mental retardation also becomes a characteristic feature.

Typically, patients with this syndrome die in early childhood, only 10% of them survive to the age of ten. However, there have also been cases of longevity with the “cry of the cat” syndrome - up to 50 years.

Wolf-Hirschhorn syndrome

This syndrome is much less common - 1 case per 100,000 births. It is caused by the deletion of one of the segments of the short arm of the fourth chromosome.

The manifestations of this disease are varied: delayed development of the physical and mental sphere, microcephaly, characteristic beak-shaped nose, strabismus, cleft palate or upper lip, small mouth, defects of internal organs.

Like many other human chromosomal mutations, Wolf-Hirschhorn disease is classified as semi-lethal. This means that the viability of the body with such a disease is significantly reduced. Children diagnosed with Wolf-Hirschhorn syndrome usually do not live beyond the age of 1 year, but one case has been recorded in which the patient lived for 26 years.

Partial trisomy syndrome on the short arm of chromosome 9

This disease occurs due to unbalanced duplications in the ninth chromosome, as a result of which there is more genetic material on this chromosome. In total, more than 200 cases of such mutations in humans are known.

The clinical picture is described by delayed physical development, mild mental retardation, and a characteristic facial expression. Heart defects are found in a quarter of all patients.

With partial trisomy syndrome of the short arm of chromosome 9, the prognosis is still relatively favorable: most patients survive to old age.

Other syndromes

Sometimes chromosomal mutations occur even in very small sections of DNA. Diseases in such cases are usually caused by duplications or deletions, and are called microduplications or microdeletions, respectively.

The most common such syndrome is Prader-Willi disease. It occurs due to microdeletion of a section of chromosome 15. Interestingly, this chromosome must be received by the body from the father. As a result of microdeletions, 12 genes are affected. Patients with this syndrome have mental retardation, obesity, and usually have small feet and hands.

Another example of such chromosomal diseases is Sotos syndrome. A microdeletion occurs on the long arm of chromosome 5. The clinical picture of this hereditary disease is characterized by rapid growth, an increase in the size of the hands and feet, the presence of a convex forehead, and some mental retardation. The incidence of this syndrome has not been established.

Chromosomal mutations, more precisely, microdeletions in areas of chromosomes 13 and 15, cause Wilms tumor and retinblastoma, respectively. Wilms tumor is a kidney cancer that occurs primarily in children. Retinoblastoma is a malignant tumor of the retina that also occurs in children. These diseases are treatable if diagnosed in the early stages. In some cases, doctors resort to surgical intervention.

Modern medicine eliminates many diseases, but it is not yet possible to cure or at least prevent chromosomal mutations. They can only be detected at the beginning of fetal development. However, genetic engineering does not stand still. Perhaps soon a way to prevent diseases caused by chromosomal mutations will be found.

Chromosomal mutations (rearrangements, or aberrations)- These are changes in the structure of chromosomes that can be identified and studied under a light microscope.

Various types of rearrangements are known:

1. a lack of, or defiance,- loss of the terminal sections of the chromosome;
2. deletion- loss of a section of a chromosome in its middle part;
3. duplication - double or multiple repetition of genes localized in a specific region of the chromosome;
4. inversion- rotation of a chromosome section by 180°, as a result of which genes in this section are located in the reverse sequence compared to the usual one;
5. translocation- change in the position of any part of a chromosome in the chromosome set. The most common type of translocations are reciprocal, in which regions are exchanged between two non-homologous chromosomes. A section of a chromosome can change its position without reciprocal exchange, remaining in the same chromosome or being included in some other one.

At deficiencies, deletions And duplications the amount of genetic material changes. The degree of phenotypic change depends on how large the corresponding chromosome regions are and whether they contain important genes. Examples of deficiencies are known in many organisms, including humans. Severe hereditary disease - "cry of the cat" syndrome(named after the nature of the sounds made by sick babies) is caused by heterozygosity for deficiency in the 5th chromosome. This syndrome is accompanied by severe growth impairment and mental retardation. Children with this syndrome usually die early, but some survive

Genomic mutations- change in the number of chromosomes in the genome of body cells. This phenomenon occurs in two directions: towards an increase in the number of entire haploid sets (polyploidy) and towards the loss or inclusion of individual chromosomes (aneuploidy).

Polyploidy- multiple increase in the haploid set of chromosomes. Cells with different numbers of haploid sets of chromosomes are called triploid (3n), tetraploid (4n), hexanloid (6n), octaploid (8n), etc.

Most often, polyploids are formed when the order of chromosome divergence to the cell poles is disrupted during meiosis or mitosis. This can be caused by physical and chemical factors. Chemicals such as colchicine suppress the formation of the mitotic spindle in cells that have begun to divide, as a result of which the duplicated chromosomes do not separate and the cell becomes tetrahedral.

For many plants the so-called polyploid series. They include forms from 2 to 10n and more. For example, a polyploid series of sets of 12, 24, 36, 48, 60, 72, 96, 108 and 144 chromosomes is made up of representatives of the genus Solanum. The genus wheat (Triticum) represents a series whose members have 34, 28 and 42 chromosomes.

Polyploidy results in changes in the characteristics of an organism and is therefore an important source of variation in evolution and selection, especially in plants. This is due to the fact that hermaphroditism (self-pollination), apomixis (parthenogenesis) and vegetative propagation are very widespread in plant organisms. Therefore, about a third of the plant species common on our planet are polyploids, and in the sharply continental conditions of the high-mountain Pamirs, up to 85% of polyploids grow. Almost all cultivated plants are also polyploids, which, unlike their wild relatives, have larger flowers, fruits and seeds, and more nutrients accumulate in storage organs (stems, tubers). Polyploids adapt more easily to unfavorable living conditions and tolerate low temperatures and drought more easily. That is why they are widespread in the northern and high mountain regions.

The basis for the sharp increase in the productivity of polyploid forms of cultivated plants is the phenomenon polymers.

Aneuploidy, or heteroploidy,- a phenomenon in which the cells of the body contain an altered number of chromosomes that is not a multiple of the haploid set. Aneuploids arise when individual homologous chromosomes do not separate or are lost during mitosis and meiosis. As a result of chromosome nondisjunction during gametogenesis, germ cells with extra chromosomes can arise, and then, upon subsequent fusion with normal haploid gametes, they form a zygote 2n + 1 (trisomic) on a specific chromosome. If there is one less chromosome in the gamete, then subsequent fertilization leads to the formation of a zygote 1n - 1 (monosomic) on any of the chromosomes. In addition, there are forms 2n - 2, or nullisomics, since there is no pair of homologous chromosomes, and 2n + X, or polysomics.

Aneuploids are found in plants and animals, as well as in humans. Aneuploid plants have low viability and fertility, and in humans this phenomenon often leads to infertility and in these cases is not inherited. In children born to mothers over 38 years of age, the likelihood of aneuploidy is increased (up to 2.5%). In addition, cases of aneuploidy in humans cause chromosomal diseases.

In dioecious animals, both under natural and artificial conditions, polyploidy is extremely rare. This is due to the fact that polyploidy, causing a change in the ratio of sex chromosomes and autosomes, leads to disruption of the conjugation of homologous chromosomes and thereby complicates sex determination. As a result, such forms turn out to be sterile and less viable.

There are several reasons for violations of the genetic program of a cell.

Changes in the biochemical structure of genes include:

• point mutations with the loss of any of the nucleotides, leading to dysfunction in the programming of genetic information;
• loss of part of a chromosome;
• polymerization with the formation of additional chromosome regions.

One or more new chromosomes may be missing or appear.

Activation of pathological genes may be related:

• with structural changes in regulatory genes,
• with activation of lethal genes due to homozygosity for autosomal recessive genes or the manifestation of pathogenic genes associated with sex.

In addition, the manifestation of a pathogenic autosomal recessive trait may be associated with another gene (linked genes and traits).

Introduction of a foreign DNA fragment with pathogenic properties into the genome, for example, a virus, can lead to cell death or persistence of the virus inside it. This persistence often leads to the occurrence of malignant tumor growth. Under experimental conditions, researchers introduce both pathological and missing genes into a cell (genetic engineering).

All of the listed genomic disorders can be transmitted by inheritance, if they arose in germ cells, or lead to somatic changes in the animal’s body without inheritance (the genome is changed in somatic cells).

The genetic material can be changed so grossly that it becomes clearly visible even when studying chromosomes using light microscopy during division. These are the so-called genomic and chromosomal mutations.

Genomic mutations lead to gross change in structure nuclear hereditary material in general. Accompanied by changes in the number and shape of chromosomes, the ratio of their content in different cells. Often, genomic mutations are characterized by aneuploidy, heteroploidy or polyploidy, which is often observed in malignant tumor cells when mitosis is impaired (with reduced mitosis). A genomic mutation may be due to the fact that one of the chromosomes is represented not by two, as usual in a somatic cell, but by three or more copies. An example of such a mutation is Down syndrome.

Chromosomal mutations occur when the structure of individual chromosomes changes, the size of the arms increases or decreases, a section of one chromosome is translocated to another, or a section of a chromosome is rotated 180°. The lack of one of the chromosome sections is called deletion. The loss of significant sections of a chromosome usually leads to the death of the organism. Duplication of a part of a chromosome - duplication A 180° reversal of a chromosome section is designated as an inversion and may not be phenotypically manifested. Exchange of regions between non-homologous chromosomes - translocation- usually leads to developmental disorders of the body that are incompatible with life.

Gene or point mutation is a replacement of individual nucleotides or small sections of the genome within one gene. The gene mutation is invisible during histological examination, but changes the phenotype of the cell, which leads to the formation of new characteristics in the cell and/or in the body as a whole.

Highlight conformational mutations when one nucleotide is replaced by another, changing the DNA double helix.

Sometimes a mutation does not change the information stored by the genome. This change in the genome is called silent mutation . If a mutation causes a distortion of the information stored by the genome, then it is called a mutation that distorts the biological meaning of hereditary information. This leads to the formation of enzymes with altered activity, providing new characteristics that are unusual for the cell and the whole organism.

Under a mutation that makes no sense , understand a gene mutation that changes the structure of a gene in such a way that reading information from it becomes impossible, or an mRNA sequence is formed that cannot be translated by the ribosome.

Mutagens - these are factors of any nature that change the structure of the genome and cause mutations. Highlight endogenous and exogenous mutagens. These may be impacts physical nature(ionizing radiation, ultraviolet radiation, injury, elevated temperature). Chemical mutagens are some pesticides, industrial poisons (benzene, benzopyrene, epoxides, some aldehydes), mercury compounds, cytostatics. Some have a mutagenic effect nutritional supplements(cyclamates, aromatic carbohydrates), lipid peroxide compounds, free oxygen radicals contained in hydrogen peroxide and ozone.

As a result of mutations, genetic diseases arise.

• Diseases caused entirely by the influence of a pathological gene. These disorders always appear regardless of the characteristics that precede the vital activity of cells and the organism as a whole. Typically, manifestations caused by such mutations can be observed from the moment the animal or person is born.
• Diseases in which the genetic factor manifests itself only in the presence of appropriate environmental conditions and characteristics of individual development. Thus, a tendency to diabetes mellitus may manifest itself depending on dietary habits. This type of hereditary disease is almost always detected after birth, sometimes in old age.
• Diseases in which heredity is the leading causative factor. The disease manifests itself, but its degree, speed and severity are different due to the level of accumulation in the body of the consequences of the influence of etiological factors that arise in the process of life.

Hereditary diseases can be transmitted by an autosomal dominant, autosomal recessive mechanism of inheritance and be sex-linked.

Hereditary diseases associated with sex are caused by the transmission of gene disorders in the sex chromosomes, therefore the manifestations of the disease are directly related to the gender of the individual.

Sometimes gene mutations are transmitted through somatic chromosomes and their occurrence is gender dependent. For example, vascular atherosclerosis, under the same conditions, develops earlier in males, since female sex hormones block the development of the disease.

Violations in the implementation of the genetic program are associated with the following phenomena.

Mitosis disorders are accompanied by uneven distribution of chromosomes (reduced mitosis or amitosis) and lead to dysplasia (the formation of monster cells).

Another possible consequence is the formation of polyploid or multinucleated cells. Massive suppression of mitosis when cells lose the ability to divide leads to impaired regeneration of organs and tissues. The reasons are changes in the regulation of the operon, damage to the cell center or microtubules, changes in cytotomy against the background of impaired formation of microtubules and actominiyosin interactions, impaired energy supply for division, etc.