Most often mean permanent change of a genotype which can be inherited by descendants by a mutation. In other words, this change of DNA of a cage. Mutations can happen because of influence of external or internal environment, for example, of ultraviolet, X-rays (radiation), etc.
Essence of gene mutations
Within formal classification distinguish:
- genomic mutations – change of quantity of chromosomes; • chromosomal mutations – reorganization of structure of separate chromosomes;
- gene mutations are changes of number and/or the sequence of components of genes (nucleotides) in structure of DNA which consequence is a change of quantity and quality of the corresponding proteinaceous products.
Gene mutations occur by replacement, a deletion (loss), a translocation (movement), duplication (doubling), inversion (change) of nucleotides within separate genes. When it is about transformations within one nucleotide, use the term – a tochkovy mutation.
Similar transformations of nucleotides become the reason of emergence of three mutant codes: • with the changed meaning (missens-mutation) when in polypeptide, replacement of one amino acid with another happens the coded this gene; • with not changed sense (neutral mutations) – replacement of nucleotides is not followed by replacement of amino acids and has no noticeable impact on structure or function of the corresponding protein; • senseless (nonsense mutation) which can become the reason of break of a polypeptide chain and possess the greatest damaging action.
Mutations in various parts of a gene
If to consider a gene about the positions of the structurally functional organization then happening in it losses, inserts, replacements and movements of nucleotides can be divided into two groups conditionally: 1. mutations in regulatory areas of a gene (in a pro-motor part and in the polyadenylation website) which cause quantitative changes of the corresponding products and are shown clinically depending on limit of proteins, but their function still remains; 2. mutations in the coding areas of a gene: • in exons – become the reason of the premature end of proteinaceous synthesis; • in introns – can generate the new websites of a splaysing which, as a result, replace initial (normal); • in the splaysing websites (in a zone of a joint of exons and introns) – lead to broadcast of senseless proteins. For elimination of consequences of such damages there are special reparation mechanisms. Which essence at a distance of the wrong site of DNA, and then on this place is restored initial. Only if the reparation mechanism did not work or did not cope with damage, there is a mutation.