A human mutation is a change that occurs in a cell at the DNA level. They can be of different types. Mutation of people can be neutral. In this case, a synonymous nucleoid replacement occurs. Changes can be harmful. They are characterized by intense phenotypic effect. Also, mutating people can be useful. In this case, the changes have a small phenotypic effect. Next, we consider in more detail how a person mutates. Examples of changes will also be given in the article.
Classification
Different types of mutations are distinguished. Some of the categories, in turn, have their own classification. In particular, the following types of mutations exist:
- Somatic.
- Chromosomal
- Cytoplasmic.
- Human genomic mutations and others.
Changes occur under the influence of various factors. One of the most striking cases of the manifestation of such changes is considered Chernobyl. Mutations of people after the disaster did not begin to appear immediately. However, over time, they became more pronounced.
Human Chromosomal Mutations
These changes are characterized by structural disturbances. Breaks occur in the chromosomes. They are accompanied by various rearrangements in the structure. Why do human mutations occur? The reasons are external factors:
- Physical . These include gamma and X-rays, ultraviolet exposure, temperature (high / low), electromagnetic field, pressure and so on.
- Chemical . This category includes alcohols, cytostatics, salts of heavy metals, phenols and other compounds.
- Biological . These include bacteria and viruses.
Spontaneous adjustment
Mutation of people in this case occurs under normal conditions. However, such changes in nature are extremely rare: for 1 million instances of a particular gene, 1-100 cases. Scientist Haldane calculated the average probability of spontaneous adjustment. She was 5 * 10-5 for a generation. The development of a spontaneous process depends on external and internal factors - the mutational pressure of the medium.
Characteristic
Chromosomal mutations are mostly classified as harmful. Pathologies that develop as a result of perestroika are often incompatible with life. The main characteristic of chromosomal mutations is randomness of rearrangement. Because of them, diverse new “coalitions” are being formed. These changes rearrange gene functions, randomly distribute elements across the genome. 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 deviations from the norm (aberrations). They are detected within one chromosome. This group of changes includes:
- Deletions . These mutations represent the loss of the internal or terminal portion of the chromosome. Perestroika of this kind can provoke many abnormalities during embryonic development (for example, congenital heart disease).
- Inversions . This change involves the rotation of the chromosomal fragment by 180 degrees. and setting it on the previous site. In this case, the 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 in humans.
Interchromosomal rearrangements (translocations) are the exchange of sites between elements that have similar genes. These changes are divided into:
- Robertson's . The formation of one metacentric instead of two acrocentric chromosomes.
- Non-reciprocal . In this case, a section of one chromosome moves to another.
- Reciprocal . With such rearrangements, an exchange occurs between the two elements.
Isochromosomal mutations occur due to the formation of chromosomal copies, mirror regions of the other two, which contain the same gene sets. Such a deviation from the norm is called a centric connection due to the fact of the transverse separation of chromatids occurring 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.
The interaction of all sorts of realignments
Genomic mutations are distinguished by changes in the number of structural elements. Gene mutations are abnormalities in the structure of genes. Chromosomal mutations affect the structure of the chromosomes themselves. The former and the latter, in turn, have the same classification for polyploidy and aneuploidy. The transitional restructuring between them is the Robertson translocation. These mutations are combined in such a direction and concept in medicine as “chromosomal abnormalities”. It includes:
- Somatic pathology. They include radiation pathology, for example.
- Intrauterine disorders. It can be spontaneous abortion, miscarriage.
- Chromosomal diseases. These include Down syndrome and others.
Today, 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 malformations. Violations are formed due to the most serious changes in DNA. Damage appears during fertilization, gamete maturation, in the initial stages of egg separation. Failure can even occur when merging perfectly healthy parent cells. This process is not yet controlled and is not fully understood.
Consequences of Changes
Complications of chromosomal mutations are usually very unfavorable for humans. Often they provoke:
- In 70% - spontaneous abortion.
- Malformations.
- In still 7.2% - stillbirth.
- The formation of tumors.
Against the background of chromosomal pathologies, the level of damage in the organs is caused by various factors: the type of anomaly, excess or insufficient material in the individual chromosome, environmental conditions, and the genotype of the organism.
Pathology groups
All chromosomal diseases are divided into two categories. The first is triggered by a violation in the number of elements. These pathologies make up the bulk of chromosomal diseases. In addition to trisomies, monosomes and other forms of polysomes, tetraploidy and triploidy are also included in this group (with them, death occurs either in the womb or in the first few hours after birth). Most often , Down syndrome is detected . Its basis is made up of 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 approximately one case out of 700. The second group includes diseases caused by structural changes in the chromosomes. The signs of these pathologies include:
- Stunted growth.
- Mental retardation.
- Roundness of the tip of the nose.
- Deep fit eyes.
- Heart defects (congenital) and others.
Some pathologies are caused by a change in the number in the 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, previously mutations that were previously harmful can become useful. As a result, such adjustments are considered material for selection. If the mutation is not affected by “silent” DNA fragments or if 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 adjustments can be detected. For this, methods of gene analysis 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 approximately constant frequency. This fact can be applied in the study of phylogeny - the analysis of family ties and the origin of various taxa, including humans. In this regard, rearrangements in the "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 constant over an extended period. However, for different genes the intensity will be different.
Finally
The study of the mechanism of occurrence and further development of rearrangements in mitochondrial deoxyribonucleic acid, which passes to the offspring of the maternal line, and in the 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 is information in the direction of the reconstruction of the biological formation and development of mankind.