A mutation is a genome inherited by descendants. Changes in hereditary material enclosed in a cell are divided into three groups. On genomic, chromosomal and gene. It is about a gene or, in another way, point mutation that will be discussed. It is she who is considered a 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, exclusion, or insertion of one nitrogenous base (pyrimidine derivatives) instead of another. Changes occur in non-coding (junk) DNA and, basically, do not manifest themselves.
The process of change occurs when DNA is doubled in living cells (replication), crossing over (exchange of homologous chromosome regions), or during other periods of the cell cycle. During the regeneration of cell structures, changes and DNA damage are eliminated. In addition, they themselves can cause mutations. For example, if a chromosome is broken, then part of the nucleophosphate pair is lost during its restoration.
If the regeneration processes for some reason do not work well enough, mutations are rapidly accumulating. 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. Nevertheless, sometimes the opposite effect occurs when a change in the genes of regeneration enzymes leads to a decrease in the mutation frequency 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 evolutionary process.
Types of point mutations
The classification of gene changes is based on the transformations that an altered nitrogen base has on a triplet. Clinically, they are manifested by symptoms of metabolic disorders in the body. Varieties of gene or point mutations:
- Missense change. By this type is meant the process of changing the genome, in which the structural unit of the genetic code encodes another amino acid. Depending on how the properties of the proteins differ from the original proteins, an acceptable, partially acceptable and unacceptable missense mutation is isolated.
- Nonsense mutation - changes in the DNA sequence, leading to a premature final stage of protein synthesis. The pathologies that they may cause may include cystic fibrosis, Hurler syndrome, and others.
- Silencing mutation - a triplet encodes the same amino acid.
Substitution mutations
There are two main classes of nitrogen base substitution mutations.
- Transition. Translated from Latin, transition means "moving." In genetics, by value is meant a point mutation in which one organic compound, a derivative of purine, is replaced by another, for example, adenine with guanine.
- Transversion is the replacement of purine base (adenine) with pyrimidine (cytosine, guanine). Also mutations of base substitution are classified as target, non-target, delayed.
Open Frame Shift Mutations
A gene reading frame is a sequence of nucleoside phosphates that can encode a protein. Mutations are contrasted with complex ones and classified as follows:
- Deletion - 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 a DNA sequence. Movements can be within the genome, an extracellular viral agent can be integrated.
In some cases, changes occur on undamaged sections of DNA. They are called non-target frame shift changes.
Gene mutations do not always develop immediately after the negative impact of a mutagen. Sometimes changes appear after several cycles of replication.
Causes of occurrence
The causes of the 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 nucleoside phosphate of DNA.
- Induced - arising due to external factors: radiation, viral agents, chemical compounds.
Substitution mutations occur for various reasons. Changes in the type of reading frame shift are spontaneous.
Examples of gene mutations
The mutation process is a source of changes that lead to various pathologies. Today, although rare, there are persistent gene changes in the hereditary material of the body’s cells.
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 to be thirty years old. Changes affect the development of strokes, heart pathologies. Strokes and heart attacks are the main cause of death in patients with progeria.
- Hypertrichosis. People with Ambras syndrome have increased hairiness. Vegetation occurs on the face, shoulders.
- Marfan's syndrome. One of the most common mutations. In patients, limbs are disproportionately developed, fusion of the ribs is observed, as a result of which the chest cages.
Mutations in modern genetics
Human evolution is not limited to the past. The mechanisms that cause mutations continue to work now. Mutation is a process characteristic of living organisms, which underlies the evolution of absolutely all life forms and consists in changing genetic information.
Genetics is an important area of biology. People use genetic methods in animal husbandry and crop production. Selecting the best populations, a person crosses them, creating the best varieties and breeds with 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 synonyms that mean 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 (abnormalities) of chromosomes are unfavorable for both an individual organism and a population. Most chromosomal abnormalities that arose during embryonic development lead to severe congenital malformations. Point mutations lead to congenital abnormalities 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 using genetic engineering.