A human mutation is a change that occurs in a cell at the DNA level. They can be of different types. Human mutation can be neutral. In this case, a synonymous substitution of nucleoids occurs. The changes can be harmful. They are characterized by an intense phenotypic effect. Mutation of humans can also be beneficial. In this case, the changes have little phenotypic effect. Next, let's take a closer look at how a person's mutation occurs. 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 various factors. Chernobyl is considered one of the brightest cases of manifestation of such changes. Mutations of people after the catastrophe did not appear immediately. However, over time they became more pronounced.
Human Chromosomal Mutations
These changes are characterized by structural disturbances. Breaks occur in chromosomes. They are accompanied by differentrestructuring in the structure. Why do human mutations occur? The reasons are external factors:
- Physical. These include gamma and x-rays, ultraviolet exposure, temperatures (high/low), electromagnetic field, pressure, and more.
- Chemical. This category includes alcohols, cytostatics, s alts of heavy metals, phenols and other compounds.
- Biological. These include bacteria and viruses.
Spontaneous adjustments
Mutation of people in this case occurs under normal conditions. However, such changes in nature are extremely rare: for 1 million copies of a particular gene, 1-100 cases. Scientist Haldane calculated the average probability of spontaneous rearrangement occurring. It amounted to 510-5 for a generation. The development of a 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 randomness of rearrangement. Because of them, diverse new "coalitions" are being formed. These changes rearrange gene functions, distribute elements randomly throughout the genome. Their adaptive value is determined by a selection process.
Chromosomal mutations: classification
There are three options for such changes. In particular, there are iso-, inter- andintrachromosomal mutations. The latter are characterized by deviations from the norm (aberations). They are found within the same chromosome. This group of changes includes:
- Deletions. These mutations represent the loss of an internal or terminal portion of a chromosome. A rearrangement of this kind can provoke many anomalies during embryonic development (for example, a congenital heart defect).
- Inversions. This change involves the rotation of the chromosome fragment by 180 degrees. and placing it in its original position. 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 human hereditary mutations.
Interchromosomal rearrangements (translocations) are the exchange of sites between elements that have similar genes. These changes are divided into:
- Robertsonian. One metacentric chromosome is formed instead of two acrocentric chromosomes.
- Non-reciprocal. In this case, a section of one chromosome moves to another.
- Reciprocal. With such rearrangements, there is an exchange between two elements.
Isochromosomal mutations arise as a result of the formation of chromosome copies, mirror sections of the other two, which contain the same gene sets. Such a deviation from the norm is called a centric connection due to the facttransverse separation of chromatids, which occurs through centromeres.
Types of changes
There are structural and numerical chromosomal 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.
Interaction of various rearrangements
Genomic mutations are distinguished by changes in the number of structural elements. Gene mutations are disturbances in the structure of genes. Chromosomal mutations affect the structure of the chromosomes themselves. The first and last, in turn, have the same classification for polyploidy and aneuploidy. The transitional 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. It can be spontaneous abortions, miscarriages.
- Chromosomal diseases. These include Down syndrome and others.
To date, about a hundred anomalies are known. All of them have been researched and described. About 300 forms are presented as syndromes.
Features of congenital pathologies
Hereditary mutations are quite extensive. This categorycharacterized by multiple developmental defects. Violations are formed due to the most serious changes in DNA. Damage occurs during fertilization, maturation of gametes, at the initial stages of egg division. Failure can even occur when perfectly he althy parental cells merge. This process today is not yet under control and has not been fully studied.
Consequences of change
Complications of chromosomal mutations are usually very unfavorable for humans. They often provoke:
- 70% spontaneous abortion.
- Defects.
- At 7.2% - stillbirth.
- Tumor formation.
Against the background of chromosomal pathologies, the level of damage in organs is determined by various factors: the type of anomaly, excess or insufficient material in an individual chromosome, environmental conditions, the genotype of the organism.
Pathology groups
All chromosomal diseases are divided into two categories. The first includes those provoked by a violation in the number of elements. These pathologies make up the bulk of chromosomal diseases. In addition to trisomy, monosomy and other forms of polysomy, this group includes tetraploidy and triploidy (in which death occurs either in the womb or in the first few hours after birth). Down syndrome is the most common. 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. Pathology occurs in about one case out of 700. The second group includes diseases caused by structural changes in the chromosomes. The signs of these pathologies include:
- Stunting.
- Mental retardation.
- Roundness of the tip of the nose.
- Deep-set eyes.
- Heart defects (congenital) and others.
Some pathologies are caused by a change in the number of sex chromosomes. Patients with these mutations do not have 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, mutations that were previously harmful can become beneficial. As a result, such rearrangements are considered material for selection. If the mutation does not affect "silent" DNA fragments or it provokes the replacement of one code fragment with a synonymous one, then, as a rule, it does not manifest itself in any way in the phenotype. However, such rearrangements can be found. For this, genetic analysis methods are used. Due to the fact that changes occur due to the influence of natural factors, then, assuming that the main characteristics of the external environment remain unchanged, it turns out that mutations appear at an approximately constant frequency. This fact can be applied in the study of phylogeny - the analysis of family ties and the origin of different taxa, including humans. In connection withThus rearrangements in "silent genes" act as a "molecular clock" for researchers. The theory also assumes that most of the changes are neutral. Their accumulation rate in a particular gene is weakly or completely independent of the influence of natural selection. As a result, the mutation becomes permanent over a long period. However, different genes will have different intensity.
In closing
Studying the mechanism of occurrence, further development of rearrangements in mitochondrial deoxyribonucleic acid, which passes to offspring through the maternal line, and in Y-chromosomes transmitted from the father, is widely used today in evolutionary biology. Collected, analyzed and systematized materials, research results are used in studies of the origin of different nationalities and races. Information is of particular importance in the direction of the reconstruction of the biological formation and development of mankind.
