Мутация людей представляет собой изменения, that occur in the cell at the DNA level. They can be of different types. Mutation of people can be neutral. In this case, synonymous nucleoid replacement occurs. Changes can be harmful. They are characterized by an intense phenotypic effect. Also mutation of people can be useful. In this case, the changes have a small phenotypic effect. Next, we take a closer look at how a person mutates. Examples of changes will also be given in the article.
Classification
There are different types of mutations. Some of the categories have, in turn, their own classification. In particular, there are the following types of mutations:
- Somatic.
- Chromosomal.
- Cytoplasmic.
- Genomic mutations in humans and others.
Changes occur under the influence of differentfactors. One of the bright cases of such changes is Chernobyl. Mutations of people after the disaster began to appear not immediately. However, over time they became more pronounced.
Human chromosomal mutations
These changes are characterized by structuralviolations. Breaks occur in the chromosomes. They are accompanied by various restructuring. Why do human mutations occur? The reasons are external factors:
- Physical. These include gamma and X-rays, ultraviolet light, temperatures (high / low), electromagnetic field, pressure, and so on.
- Chemical. This category includes alcohols, cytostatics, heavy metal salts, phenols and other compounds.
- Biological. These include bacteria and viruses.
Spontaneous adjustment
A mutation of people in this case occurs innormal conditions. However, such changes in nature are extremely rare: for 1 million instances of a specific gene, 1-100 cases. The scientist Haldane calculated the average probability of spontaneous adjustment. It amounted to a generation of 5 * 10-5. The development of a spontaneous process depends on external and internal factors - the mutational pressure of the environment.
Characteristic
Chromosomal mutations for the most part includeto the category of harmful. Pathologies that develop as a result of reorganizations are often incompatible with life. The main characteristic of chromosomal mutations is the randomness of restructuring. Because of them, diverse new "coalitions" are being formed. These changes rearrange gene functions, distribute elements across the genome randomly. Their adaptive value is determined in the selection process.
Chromosomal mutations: classification
There are three options for such changes.In particular, iso-, inter- and intrachromosomal mutations are isolated. The latter are characterized by abnormalities (aberrations). They are detected within a single chromosome. This group of changes includes:
- Deletions. These mutations are lossinternal or terminal region of the chromosome. A restructuring of this kind can provoke many abnormalities during embryonic development (for example, congenital heart disease).
- Inversion. This change assumes rotationchromosomal fragment 180 degrees. and setting it on the former site. At the same time, the order of arrangement of structural elements is violated, but this does not affect the phenotype if there are no additional factors.
- Duplications. They represent the multiplication of a fragment of a chromosome. Such a deviation from the norm provokes hereditary mutations of a person.
Interchromosomal rearrangements (translocations) are an exchange of sites between elements that have similar genes. These changes are divided into:
- Robertsonovskie. The formation of one metacentric instead of two acrocentric chromosomes.
- Non-reciprocal. In this case, the area of one chromosome moves to another.
- Reciprocal. At such rearrangements there is an exchange between two elements.
Isochromosomal mutations occur due tothe formation of chromosome copies, mirror sections of the other two, which contain the same gene sets. Such a deviation from the norm is referred to as a centric compound due to the fact that the chromatids are transversely separated by centromeres.
Types of changes
There are structural and numerical chromosomalmutations. The latter, in turn, are divided into aneuploidy (this is the appearance (trisomy) or loss (monosomy) of additional elements) and polyploidy (this is a multiple increase in their number).
The interaction of various kinds of restructuring
Genomic mutations are characterized by changes innumber of structural elements. Gene mutations are disorders in the structure of genes. Chromosomal mutations affect the structure of the chromosomes themselves. The first and last, in turn, have the same classification by polyploidy and aneuploidy. Transitional restructuring between them is the Robertsonian translocation. These mutations are united in such a direction and concept in medicine as "chromosomal abnormalities". It includes:
- Somatic pathology. These include radiation pathology, for example.
- Intrauterine disorders. This may be spontaneous abortions, miscarriages.
- Chromosomal diseases. These include Down syndrome and others.
Today we know about a hundred anomalies. All of them are investigated and described. About 300 forms are presented as syndromes.
Features of congenital abnormalities
Hereditary mutations are presented fairlyextensively. This category is characterized by multiple evils in development. Violations are formed due to the most serious changes in DNA. Damage occurs during fertilization, maturation of gametes, in the initial stages of the separation of the egg. Failure may even occur when a completely healthy parental cells merge. This process today is still uncontrollable and not fully understood.
Effects of change
Complications of chromosomal mutations, as a rule, are very unfavorable for humans. Often they provoke:
- In 70% - spontaneous abortion.
- Malformations.
- In 7.2% stillbirth.
- The formation of tumors.
Against the background of chromosomal pathologies, the level of damage inorgans are caused by various factors: the type of anomaly, excessive or insufficient material in the individual chromosome, environmental conditions, the genotype of the organism.
Pathology groups
All chromosomal diseases are divided into twocategories. The first is caused by a violation in the number of elements. These pathologies constitute the bulk of chromosomal diseases. In addition to trisomy, monosomy, and other forms of polysomies, tetraploidy and triploidy are included in this group (death occurs either in the womb or in the first few hours after birth). Most often revealed Down syndrome. It is based on genetic defects. Down's disease is named after the pediatrician who described it in 1886. Today, this syndrome is considered the most studied of all chromosomal abnormalities. There is a pathology in about one of 700 cases. The second group includes diseases caused by structural changes in the chromosomes. The signs of these pathologies include:
- Growth retardation
- Mental retardation.
- Roundness of the tip of the nose.
- Deep landing eyes.
- Heart defects (congenital) and others.
Some pathologies are caused by a change.quantities in sex chromosomes. Patients with such mutations have no offspring. To date, there is no clearly developed etiological treatment of such diseases. However, diseases can be prevented through prenatal diagnosis.
Role in evolution
Against the background of pronounced changes in conditions, the formerharmful mutations can be beneficial. As a result, such rearrangements are considered material for selection. If the “silent” DNA fragments are not affected by the mutation or it provokes the replacement of one code fragment with a synonym, then, as a rule, it does not manifest itself in any way in the phenotype. However, such adjustment can be detected. For this, methods of gene analysis are used. Due to the fact that changes occur due to the impact of natural factors, then, assuming that the main characteristics of the external environment remain unchanged, it turns out that mutations appear approximately at a constant frequency. This fact can be applied in the study of phylogeny - analysis of kinship and the origin of different taxa, including humans. In this regard, the restructuring in the "silent genes" act as a "molecular clock" for researchers. The theory also assumes that most changes are neutral. Their rate of accumulation in a particular gene is weak or completely independent of the influence of natural selection. As a result, the mutation becomes constant over a long period. However, for different genes the intensity will be different.
Finally
Изучение механизма возникновения, дальнейшего development of rearrangements in the mitochondrial deoxyribonucleic acid, which goes to the offspring on the maternal line, and in Y-chromosomes transmitted from the father, is widely used today in evolutionary biology. The collected, analyzed and systematized materials, research results are used in studies of the origin of different nationalities and races. Of particular importance are the information in the direction of the reconstruction of the biological formation and development of mankind.
