Quite often found in nature phenomenon called chromosomal mutations.It is associated with a change in the structure or number of chromosomes and lead to further development of various defects in the body.Mutations of chromosomes are divided into structural (there is a change in their structure) and numeric (characterized by a change in the number of chromosomes in a pair of the genome).
structural chromosomal mutations. This disorder is associated with a discontinuity, and subsequent binding of chromosome, resulting in a change of the original genetic material.They can be:
- balanced - in this case there is a shortage or an excess of genetic material, so in most cases they do not appear.But there is a huge risk of transmission of an unbalanced set of genetic material in reproduction.
- unbalanced - in this case the unborn child has a number of severe pathologies.
are the following ways to change the structure of chromosomes:
- Deletions - chromosomal mutations that are associated with chromosomal strand break and the loss of its important parts.Such changes lead to serious consequences, and in some cases death.
- Duplications - mutations that are associated with a doubling of a specific region of DNA, with no serious pathology.
- Translocation - carried out at break of two adjacent chromosomes.As a result, the two chromosomes exchange their units, forming a new set of genetic material.
- Insetsii - characterized by the transfer portion of one chromosome to another.
- Inversions - with this form of break chromosome mutation occurs in two places at once.Thereafter, the portion that is located between the discontinuities, is rotated about an axis, changing the genetic sequence.
numerical chromosomal mutations .As already mentioned, such mutations are associated with changes in chromosome number.The following types:
- Trisomy - chromosomal mutation, which is accompanied by the appearance of the genetic set of an extra chromosome.This happens if during cell division daughter chromosomes are not at odds.Such changes cause and phenotypic pathology.Some of trisomy lead to fetal death in the early stages of its development.Causes of mutations is not yet fully understood.
- monosomy - chromosomal mutation which is characterized by the disappearance of one chromosome.In most cases, such an organism is not viable, however he died at early stages of embryonic development.
- Poliplodiya - a very rare phenomenon, which is characterized by the presence in the cell tripled, and sometimes even quadruple set of chromosomes.The body with such disabilities can not live - or he dies before birth or shortly after.
- numerical changes in the sex chromosomes - a fairly common phenomenon, which is accompanied by an increase in the number of chromosomes in the last twenty-third pair.
chromosomal mutations: examples
Modern medicine knows many cases of children born with chromosomal defects.As mentioned earlier, some chromosomal mutations do not cause visible reactions of the body, and some are simply not compatible with survival.But there is a fairly well-known genetic diseases that occur is due to changes in the genetic material.
example, Down syndrome - trisomy 21 is a pair of chromosomes.Such a violation is accompanied by congenital malformations of the heart and circulatory system, as well as features in the appearance of the person and mental retardation.
Patau syndrome - trisomy 13 pair.Followed by a similar wrong development of bones, changes in the shape of the skull, polydactyl on the legs or arms (six fingers), in violation of the cardiovascular and nervous systems.
Turner Syndrome - a monosomy 23 (sexual) pair of chromosomes, causing the fetus receives only one X chromosome.These people slow the development of the reproductive system, and weak expression of secondary sexual characteristics.
