The term "mutation" goes back to the Latin word "mutatio", which literally means change or change. Mutational variability denotes persistent and obvious changes in genetic material, which is displayed in hereditary traits. This is precisely the first link in the chain of formation of hereditary diseases and pathogenesis. This phenomenon began to be actively studied only in the second half of the 20th century, and nowadays one can increasingly hear that mutational variability should be studied, since knowledge and understanding of this mechanism becomes key to overcoming the problems of mankind.
There are several types of mutations in cells. Their classification depends on the variety of the cells themselves. Generative mutations occur in germ cells, and gametic cells also exist. Any changes are inherited and often found in the cells of descendants, from generation to generation a number of deviations are transmitted, which eventually become the cause of diseases.
Somatic mutations are related to asexual cells. Their peculiarity is that they appear only in the individual in whom they appeared. Those. changes are not inherited by other cells, but only when dividing in one organism. Somatic mutational variation is more pronounced when it begins in the early stages. If a mutation occurs in the first stages of zygote fragmentation, then more cell lines with different genotypes will appear. Accordingly, already more cells will carry the mutation, such organisms are called mosaic.
Inheritance Levels
Mutational variability is manifested in hereditary structures that differ in different levels of organization. Mutations can occur at the gene, chromosomal and genomic levels. Depending on this, the types of mutational variability also change.
Gene changes affect the structure of DNA, as a result of which it changes at the molecular level. Such changes in some cases do not affect the viability of the protein, i.e. functions do not change in any way. But in other cases, defective formations can occur, which already ceases the ability of the protein to perform its function.
Mutations at the chromosomal level already pose a more serious threat, because they affect the formation of chromosomal diseases. The result of this variability is changes in the structure of chromosomes, and several genes are already involved here. Because of this, the usual diploid set can change, which in turn can affect DNA as a whole.
Genomic mutations as well as chromosomal mutations can cause the formation of a chromosomal disease. Examples of mutational variation at this level are aneuploidy and polyploidy. This is an increase or decrease in the number of chromosomes, which for humans are most often fatal.
Trisomy refers to genomic mutations, meaning the presence of three homologous chromosomes in the karyotype (an increase in the number). Such a deviation leads to the formation of Edwards syndrome and Down syndrome. Monosomy means the presence of only one of two homologous chromosomes (reduction in number), which virtually eliminates the normal development of the embryo.
The reason for the occurrence of such phenomena are violations at different stages of the development of germ cells. This happens as a result of anaphase lag - homologous chromosomes during cell division move to the poles, and one of them may lag. There is also the concept of "nondisjunction" when the chromosomes could not separate at the stage of mitosis or meiosis. The result is a manifestation of violations of varying severity. Studying this phenomenon will help to unravel the mechanisms and, probably, will make it possible to predict and influence these processes.