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 (a change in their structure is observed) and numerical (characterized by a change in the number of chromosomes in the genome pair).
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 can be:
- balanced - in this case there is no shortage or excess of genetic material, so in most cases they do not appear. But there is a huge risk of transmitting an unbalanced set of genetic material during reproduction.
- unbalanced - in this case, the born child has a number of serious pathologies.
The following methods of changing the structure of chromosomes are distinguished:
- Deletions are chromosomal mutations that are associated with rupture of the chromosomal filament and the loss of its important part. Such changes lead to serious consequences, and in some cases to death.
- Duplications - mutations that are associated with the doubling of a certain section of DNA, while severe pathologies are absent.
- Translocation - performed when two adjacent chromosomes break. As a result of this, both chromosomes exchange their parts, forming a new set of genetic material.
- Insecia - characterized by the transfer of a section of one chromosome to another.
- Inversions - with this form of mutation, a chromosome break occurs in two places at the same time. After that, that section, which is located between the gaps, rotates around the axis, changing the genetic sequence.
Numerical chromosome mutations . As already mentioned, this kind of mutation is associated with a change in the number of chromosomes. The following types are distinguished:
- Trisomy is a chromosomal mutation that is accompanied by the appearance of an additional chromosome in the genetic set. This occurs if, during cell division, the daughter chromosomes do not diverge. Similar changes cause phenotypic pathologies. Some trisomies lead to fetal death in the fetus already in the early stages of its development. The causes of the mutation have not yet been elucidated.
- Monosomy is a chromosomal mutation that is characterized by the disappearance of one chromosome. In most cases, such an organism is not viable; therefore, it dies in the early stages of embryonic development.
- Polyplodia is a very rare phenomenon, which is characterized by the presence in the cell of a tripled, and sometimes even quadruple, set of chromosomes. An organism with such deviations is not able to live - it either dies before childbirth, or immediately after them.
- Numerical changes in the sex chromosomes are 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 changes in genetic material.
For example, Down syndrome is trisomy for 21 pairs of chromosomes. Such a violation is accompanied by congenital malformations of the heart and circulatory system, as well as features in the appearance of a person and a delay in mental development.
Patau syndrome - trisomy of 13 pairs. Such a violation is accompanied by abnormal bone development, changes in the shape of the skull, multi-fingering on the legs or arms (six fingers), and a violation in the work of the cardiovascular and nervous systems.
Turner syndrome is a monosomy of 23 (sexual) pairs 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.