Types of mutations

Basic types are:

• gene mutations,
• chromosomal mutations,
• genomic,
• cytoplasmic.

The listed types of mutations can occur in both sex and somatic cells. In the latter case, they can be transferred to the next generation of organisms only via vegetative reproduction.

Regardless of the type of mutation, most of them are harmful and are removed from a population in the process of natural selection. However, there are neutral or even useful mutations that increase the viability of an organism. In addition, changes in genes, harmful and neutral in certain environmental conditions, in others become useful.

Also mutations are divided into spontaneous and induced. The first arise less often and accidentally. The second results of the action of mutagens: chemicals, various radiations, biological objects, for example, viruses.

Gene mutations

This type of mutations affects the change of one gene. In turn, different types of gene mutations are distinguished:

• Substitution of one complementary nucleotide pair on another. For example, A-T is replaced by G-C. In another way, such gene mutations are called point mutations.
• Insertion or removal of a complementary pair of nucleotides, possibly several, leading to a shift in the reading frame during transcription.
• Inversion (a 180° turn) of a small portion of the DNA molecule affecting only one gene.

The main sources of gene mutations are errors in the processes of replication, repair, and cross-over. They can occur spontaneously or under the action of various chemicals.

As a result of gene mutations, the sequence of nucleotides in the genes changes. This means that when the translation of such genes occurs, the sequence of amino acids in the protein changes. If there was only a substitution of one nucleotide for another, then in the protein in place of one amino acid may be another. However, due to the redundancy of the genetic code, the altered codon can encode the same amino acid as the original one. In this case, the mutation has no consequences.

The shift of the reading frame is a more dangerous kind of gene mutations, since it leads to changes in an essential part of the peptide molecule or its synthesis is generally meaningless.

Gene mutations give a lot of alleles of the same gene. Most gene mutations persist in a recessive state. If a dominant gene mutates, then the probability of death of an offspring is great, and consequently this gene will disappear, since most mutations are harmful.

Chromosomal mutations

Chromosomal mutations arise as a result of chromosome rearrangement, when DNA regions involving many genes are affected. Such rearrangements of the genotype are more dangerous than the genetic ones, and often lead to the launch of mechanisms of self-destruction in the cell, since it can no longer divide.

With conjugation and other processes, parts of the chromosomes may be lost, doubled and inverted, and exchanges between non-homologous chromosomes may occur.

Chromosomal mutations usually arise because of the breaks of a chromatids, after which they are joined in a different way.

Genomic mutations

Genomic mutations affect not individual genes and parts of the chromosome, but the whole genome of the cell, as a result, the number of chromosomes changes. This type of mutation arises as a result of errors in the divergence of chromosomes in the process of meiosis.

The change in the number of chromosomes in the reproductive cell can be a multiple (2n, 3n, etc., instead of n) or non-multiple (eg, n + 1, n + 2). A multiple change is called polyploidy, non-multiple - aneuploidy.

Polyploidy is widespread in the world of plants, although there are also animals, which in the process of evolution arose precisely through a multiple increase in the number of chromosomes.

Aneuploidy usually leads to loss or decrease in the viability of the body, whereas polyploidy increases the size of cells and organs.

Cytoplasmic mutations

DNA is contained not only in the nucleus, but also in mitochondria and chloroplasts. The DNA of these organelles can also mutate and be transmitted to the next generation of cells and organisms.

In the case of germ cells, cytoplasmic mutations are usually transmitted along the female line, since the egg is larger than the spermatozoon and includes many organelles.