Mutation is a change in the genome inherited by descendants. Changes in the hereditary material enclosed in the cell are divided into three groups. On genomic, chromosomal and gene. It is about gene or, in other words, point mutation that will be discussed. It is she who is considered the real problem in modern genetics.
What is a point mutation?
Gene changes are more common than chromosomal and polyploid (genomic). What it is? Point mutations are the substitution, deletion, or insertion of one nitrogenous base (pyrimidine derivatives) in place of another. Changes occur in non-coding (junk) DNA and generally do not manifest themselves.
The process of change occurs when DNA is duplicated in living cells (replication), crossing over (exchange of homologous regions of chromosomes) or at other periods of the cell cycle. During the regeneration of cellular structures, changes and damage to DNA are eliminated. In addition, they themselves can cause mutations. For example, if a chromosome is broken, then when itrecovery, part of the nucleosite phosphate pair is lost.
If the regeneration processes for some reason do not work well enough, mutations rapidly accumulate. If changes have occurred in the genes responsible for repair, the work of one or many elements may be interrupted. As a result, the number of mutations will increase dramatically. However, sometimes the opposite effect occurs, when a change in the genes of regeneration enzymes leads to a decrease in the frequency of mutations of other structural units of heredity.
Most point mutations, like others, are harmful. Their occurrence with useful signs occurs infrequently. But they are the basis of the process of evolution.
Types of point mutations
The classification of gene changes is based on the transformations that the changed nitrogenous base has on the triplet. Clinically, they are manifested by symptoms of metabolic disorders in the body. Varieties of gene or point mutations:
- Missense change. This species refers to the process of changing the genome, in which the structural unit of the genetic code encodes a different amino acid. Depending on how the properties of proteins differ from the original proteins, acceptable, partially acceptable and unacceptable missense mutations are distinguished.
- Nonsense mutation - changes in the DNA sequence, leading to a premature final stage of protein synthesis. Pathologies that they can cause include cystic fibrosis, Hurler syndrome and others.
- Silence mutation - tripletcodes for the same amino acid.
Base substitution mutations
There are two main classes of nitrogenous base substitution mutations.
- Transition. Translated from Latin, transition means "moving". In genetics, value refers to a point mutation, in which one organic compound, a purine derivative, is replaced by another, for example, adenine for guanine.
- Transversion - replacement of a purine base (adenine) with a pyrimidine base (cytosine, guanine). Base substitution mutations are also classified into target, non-target, delayed.
Open reading frame shift mutations
The reading frame of a gene is a sequence of nucleoside phosphates capable of encoding a protein. Mutations are contrasted with complex ones and classified as follows:
- Deletion is the loss of one or more nucleoside phosphates from a DNA molecule. According to the localization of the lost site, deletions are divided into internal and terminal. In some cases, this type of mutation leads to the development of schizophrenia.
- Insertion is a mutation characterized by the insertion of nucleotides into the DNA sequence. Movements can be within the genome, an extracellular viral agent can be integrated.
In some cases, changes occur in undamaged sections of DNA. These are called non-target frameshift changes.
Gene mutations do not always develop immediately after the negative impact of a mutagen. Sometimes changes appear after a fewreplication cycles.
Causes of occurrence
The causes of a point mutation are divided into two groups:
- Spontaneous - developing for no apparent reason. The frequency of spontaneous mutations is from 10⁻¹² to 10⁻⁹ for each DNA nucleoside phosphate.
- Induced - arising from the influence of external factors: radiation, viral agents, chemical compounds.
Substitution type mutations occur for various reasons. Changes in the type of frameshift are spontaneous.
Examples of gene mutations
The mutation process is the source of changes that lead to various pathologies. To date, although rare, there are persistent changes in the genetic material of the cell of the body.
Examples of point mutations:
- Progeria. A rare defect characterized by premature aging of all organs and the body as a whole. People with this mutation rarely live beyond their thirties. Changes affect the development of strokes, heart pathologies. Strokes and heart attacks are the leading cause of death in patients with Progeria.
- Hypertrichosis. People with Ambras syndrome are characterized by increased hairiness. Vegetation occurs on the face, shoulders.
- Marfan syndrome. One of the most common mutations. Patients have disproportionately developed limbs, fusion of the ribs is observed, as a result of which the chest sinks.
Mutations in modern genetics
Human evolution is notlimited by the past. The mechanisms that cause mutations continue to work today. Mutation is a process inherent in living organisms, which underlies the evolution of absolutely all forms of life and consists in changing genetic information.
Genetics is an important area of biology. People use genetic methods in animal husbandry and crop production. By selecting the best populations, a person crosses them, creating the best varieties and breeds that have the necessary qualities. Genetics has achieved high positive results in explaining the nature of heredity. But unfortunately, it still cannot rule out independent changes in the genome.
Gene and point mutations are synonymous, meaning a change in one or more nucleotides. In this case, one nitrogenous base can be replaced by another, fall out, duplicate or turn 180 °.
We can confidently say that the change in genes and almost all aberrations (deviations from the norm) of chromosomes are unfavorable both for an individual organism and for a population. Most chromosomal abnormalities that occur during embryonic development lead to severe congenital malformations. Point mutations lead to congenital pathologies or system defects.
The task of science is to determine how to prevent or at least reduce the likelihood of mutations and eliminate changes in DNA through genetic engineering.
