Mutation of people. Chromosomal mutations in humans

The mutation of humans is a change that takes place in a cell at the level of DNA. They can be of different types. The mutation of people can be neutral. In this case, a synonymous replacement of nucleoids 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, let us consider in more detail how a human mutation occurs. Examples of changes will also be given in the article.

Classification

Allocate 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 different factors. Chernobyl is considered one of the brightest manifestations of such changes. Mutations of people after the disaster began to appear not immediately. However, over time they became more pronounced.

Chromosomal mutations in humans

These changes are characterized by structural disturbances. Gaps occur in chromosomes. They are accompanied by various rearrangements in the structure. Why do human mutations arise? The reasons are external factors:

• Physical . These include gamma and X-rays, ultraviolet, temperature (high / low), electromagnetic field, pressure and so on.
• Chemical . This category includes alcohols, cytostatics, heavy metal salts, phenols and other compounds.
• Biological . They include bacteria and viruses.

Spontaneous restructuring

The mutation of people in this case occurs in normal conditions. However, such changes in nature are extremely rare: 1 million copies of a certain gene are 1-100 cases. The scientist Haldane calculated the average probability of spontaneous restructuring. It amounted to a generation of 5 * 10-5. The development of the spontaneous process depends on external and internal factors - the mutational pressure of the environment.

Characteristic

Chromosomal mutations are mostly classified as harmful. Pathologies that develop as a result of restructuring are often incompatible with life. The main characteristic of chromosomal mutations is the chance of perestroika. Because of them, diverse new "coalitions" are being formed. These changes rearrange the gene functions, distribute the elements by genome randomly. Their adaptive value is determined in the selection process.

Chromosomal mutations: classification

There are three options for such changes. In particular, isolate iso-, inter- and intrachromosomal mutations. The latter are characterized by abnormalities (aberrations). They are detected within a single chromosome. This group of changes includes:

• Deletions . These mutations represent the loss of the inner or terminal portion of the chromosome. A restructuring of this kind can provoke a variety of anomalies during embryonic development (eg, congenital heart disease).
• Inversion . This change involves the rotation of the chromosome fragment by 180 degrees. And putting him on the previous plot. At the same time, the order of the arrangement of structural elements is disrupted, but this does not affect the phenotype unless there are additional factors.
• Duplications . They represent the multiplication of a fragment of a chromosome. Such deviation from the norm provokes hereditary mutations of a person.

Interchromosomal rearrangements (translocations) are the exchange of sites between elements that share similar genes. These changes are divided into:

• Robertsonovsky . A metacentric is formed instead of two acrocentric chromosomes.
• Non-offensive . In this case, the site of one chromosome moves to another.
• Reciprocal . With such rearrangements, there is an exchange between the two elements.

Isochromosomal mutations arise due to the formation of chromosomal copies, mirror regions of the other two, which contain the same gene sets. This deviation from the norm is referred to as the centric connection due to the fact of the cross-sectional separation of the chromatids, which takes place through the centromores.

Types of changes

There are structural and numerical chromosome mutations. 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). Structural rearrangements are represented by inversions, deletions, translocations, insertions, centric rings and isochromosomes.

The interaction of various rearrangements

Genomic mutations are distinguished by changes in the number of structural elements. Gene mutations are disorders in the structure of genes. Chromosome mutations affect the structure of the chromosomes themselves. The first and last, in turn, have the same classification for polyploidy and aneuploidy. Transitive rearrangement between them is the Robertsonian translocation. These mutations are united by such a direction and concept in medicine as "chromosomal abnormalities". It includes:

• Somatic pathologies. These include radiation pathology, for example.
• Intrauterine disorders. These can be spontaneous abortions, miscarriages.
• Chromosomal diseases. They include Down syndrome and others.

To date, about a hundred anomalies are known. All of them are investigated and described. About 300 forms are presented as syndromes.

Features of congenital pathologies

Hereditary mutations are represented quite extensively. This category is characterized by multiple vices in development. Disorders are formed due to the most serious changes in DNA. Damage occurs when fertilization, maturing gametes, at the initial stages of separation of the egg. Failure can even occur when merging perfectly healthy parental cells. This process is not yet controlled and is not fully understood.

Consequences of changes

Complications of chromosomal mutations, as a rule, are very unfavorable for humans. Often they provoke:

• In 70% - spontaneous abortion.
• Developmental flaws.
• In 7.2% - stillbirth.
• Formation of tumors.

Against the background of chromosomal pathologies, the level of lesion in the organs is due to various factors: the type of anomaly, excess or insufficient material in the individual chromosome, environmental conditions, genotype of the organism.

Groups of pathologies

All chromosomal diseases are divided into two categories. The first is attributed to the violation in the number of elements. These pathologies constitute the bulk of chromosomal diseases. In addition to trisomy, monosomy and other forms of polysomy, tetraploidy and triploidy are included in this group (with them death occurs either in the womb or in the first few hours after birth). The most common syndrome is Down syndrome. Its basis is made up of genetic defects. Down's disease is named after the pediatrician who described her in 1886. Today, this syndrome is considered the most studied of all chromosomal abnormalities. There is a pathology in about one case out of 700. The second group includes diseases caused by structural changes in chromosomes. The signs of these pathologies include:

• Delay in growth.
• Mental retardation.
• Roundness of the tip of the nose.
• Deep ears.
• Heart defects (congenital) and others.

Some pathologies are caused by a change in the number of sex chromosomes. Patients with such mutations have no offspring. To date, there is no well-developed etiological treatment of such diseases. However, it is possible to prevent diseases through prenatal diagnosis.

Role in evolution

Against the backdrop of pronounced changes in conditions, previously harmful mutations can be useful. As a result, such adjustment is considered a material for selection. If the "silent" fragments of DNA 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. Nevertheless, such adjustment can be detected. For this, methods of gene analysis are used. Due to the fact that changes occur due to natural factors, then assuming that the main characteristics of the external environment remain unchanged, it appears that the mutations appear approximately at a constant frequency. This fact can be applied in the study of phylogeny - analysis of kinship ties and the origin of different taxa, including humans. In connection with this, perestroika in "silent genes" advocate for researchers as "molecular clocks". The theory also assumes that most of the changes are neutral. Their rate of accumulation in a particular gene is weak or completely independent of the effect of natural selection. As a result, the mutation becomes permanent over an extended period. Nevertheless, for different genes the intensity will be different.

Finally

The study of the mechanism of the appearance, further development of the rearrangements in mitochondrial deoxyribonucleic acid, which passes to the progeny along the maternal line, and in Y-chromosomes transmitted from the father, is widely used today in evolutionary biology. Collected, analyzed and systematized materials, the results of research are used in studies of the origin of different nationalities and races. Special attention is paid to the reconstruction of the biological formation and development of mankind.