| Classification of mutations:
According to varied criteria, several classifications of mutations exist. Muller suggested to divide mutations according to the nature of changes in the functioning of genes into hypomorphic (the changed alleles operate in the same direction as wild type alleles; synthesized only less protein product), amorphous (the mutation looks at the full loss of gene, for example, the mutation white in Drosophila), antimorphic (the mutant feature changes; for example, color of the grain of corn changes from purple into brown) and neomorphic.
The more formal classifications, based on the nature of the structural changes of individual genes, chromosomes and genomes as a whole is accepted in modern educational literature. The following types of mutations are distinguished within the frameworks of this classification:
* Gene or point (the change of the molecular structure of the genes, occurring due to the replacement, insertion or deletion of nucleotides);
* Chromosomal (the structural changes of chromosomes, appearing due to the translocation or deletion of chromosomes, significant on the extension of parts);
* Genome (changes in the numbers of chromosomes).
Mutagenesis – incorporating changes in the nucleotide sequence of DNA (mutations). Two types of mutagenesis are: Natural (spontaneous) and artificial (induced) mutagenesis.
Natural or spontaneous mutagenesis occurs due to the influence of mutagenic factors of the environment such as UV radiation and chemical mutagens on the genetic material of living organisms.
Artificial mutagenesis is widely used for studying proteins and improving their properties (directional evolution).
Changes with a specific probability are incorporated into the DNA sequence using the non-directional mutagenesis method. Various chemical and physical influences - mutagen substances, UV and radiation can be mutagenic factors (mutagens). Screening and selection on those, which satisfy the mutagenesis purpose, are done after obtaining mutant organisms. Non-directional mutagenesis is more labor-consuming and carrying it out is justified if the effective mutant screening system is developed.
Changes are incorporated in the DNA in much earlier known sites in directional (site-specific) mutagenesis. For this purpose, to carry out synthesis of the short single-stranded molecules of DNA (primers), complementary target DNA except the mutation place.
The uridine matrix i.e. is the same molecule in which the remains of thymine are replaced with uracil, is obtained for bacterial plasmids (extra chromosomal circular DNA). The primer is annealed on a matrix and the completion of it into vitro with the help of polymerases up to circular DNA, complementary uridine matrix. Bacterial cells are transformed by two-stranded hybrid DNA and uridine matrix inside the cells is broken into foreign and the second strand is completed on the mutant single-stranded circular DNA. The efficiency of such mutagenesis methods is less than 100%.
PCR allows in carrying out site-directed mutagenesis with the use of a pair of primers, carrying mutation and also random mutagenesis. In the last case, mistakes in the DNA sequence are incorporated by polymerase in conditions lowering its specificity.
Mutation in the news: Recently, a southwestern Indiana farmer found a sick bald eagle that subsequently tested positive for mercury poisoning. State wildlife officials state that it remains unclear if the bird was poisoned by eating contaminated fish caught in an Indiana waterway. One environmental watchdog organization stated that the state ranks fourth national in mercury emissions from coal-fired power plants, the contamination ultimately ending up in the food chain. Catherine Bowe of the National Wildlife Federation stated that the eagle should send a strong message to people in regard to environmental contamination.
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