Chromosome mutations: a brief description and classification

Quite often in nature there is a phenomenon called chromosomal mutations. It is associated with a change in the structure or number of chromosomes and leads to the further development of various defects in the body. Mutations of chromosomes are usually divided into structural chromosomes (there is a change in their structure) and numerical (characterized by a change in the number of chromosomes in a pair of genomes).

Structural chromosomal mutations. This is a violation that is associated with the rupture and subsequent binding of chromosome regions, as a result of which the original genetic material changes. They may be:

- balanced - in this case there is no deficit or excess of genetic material, so in most cases they are not manifested in any way. But there is a huge risk of transferring an unbalanced set of genetic material during reproduction.

- unbalanced - in this case the child born has a number of severe pathologies.

There are the following ways to change the structure of chromosomes:

• Deletions are chromosomal mutations that are associated with the rupture of the chromosomal strand and the loss of its important part. Such changes lead to severe consequences, and in some cases also to death.
• Duplications are mutations that are associated with the doubling of a specific region of DNA, with severe pathologies absent.
• Translocation - is carried out by rupture of two adjacent chromosomes. As a result, both chromosomes exchange their parts, forming a new set of genetic material.
• Injections - characterized by the transfer of a section of one chromosome to another.
• Inversion - with this form of mutation, the chromosome break occurs in two places simultaneously. After that, the area that is located between the breaks, rotates around the axis, changing the genetic sequence.

Numerical chromosomal mutations . As already mentioned, these kinds of mutations are associated with a change in the number of chromosomes. There are the following types:

• Trisomy is a chromosomal mutation, which is accompanied by the appearance in the genetic set of an additional chromosome. This happens if the daughter chromosomes do not diverge during cell division . Similar changes cause and phenotypic pathologies. Some trisomies lead to intrauterine fetal death already at the early stages of its development. The causes of the mutation to the end has not yet been clarified.
• Monosomy is a chromosomal mutation, which is characterized by the disappearance of one chromosome. In most cases, such an organism is not viable, so it dies in the early stages of embryonic development.
• Polyploidy is a very rare phenomenon that is characterized by the presence in a cell of a triple, and sometimes even quadruple, chromosome. An organism with such deviations is not able to live - it either dies before the birth, or immediately afterwards.
• Numerical changes in sex chromosomes - a fairly common phenomenon, which is accompanied by an increase in the number of chromosomes in the last, 23rd pair.

Chromosomal mutations: examples

Modern medicine knows many cases of the birth of children with chromosomal defects. As mentioned earlier, some chromosomal mutations do not cause visible reactions from the body, and some are simply not compatible with survival. But there are also fairly well-known genetic diseases that arise precisely as a result of a change in genetic material.

For example, Down syndrome is a trisomy of 21 pairs of chromosomes. Such a disorder is accompanied by congenital heart and circulatory defects , as well as features in the appearance of a person and a delay in mental development.

The Patau syndrome is trisomy in 13 pairs. Accompanying such a violation is the incorrect development of bones, changes in the shape of the skull, mnogopalosti on the legs or hands (six fingers), a violation in the work of the cardiovascular and nervous systems.

Turner syndrome is a monosomy of the 23 (sexual) pair of chromosomes, as a result of which the fetus receives only one X chromosome. Such people have a slow development of the reproductive system and a weak manifestation of secondary sexual characteristics.