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| | Classification of mutations:
According to varied criteria, several classifications of mutations exist. Muller suggested to divide mutations according to nature of changes in functioning of gene into hypomorphic (changed alleles operate in the same direction as wild type alleles; synthesized only less protein product), amorphous (mutation looks as full loss of gene, for example, mutation white in Drosophila), antimorphic (mutant feature changes; for example, color of grain of corn changes from purple into brown) & neomorphic.
More formal classification, based on the nature of structural changes of individual genes, chromosomes & genome as a whole is accepted in modern educational literature. The following types of mutations are distinguished within the frameworks of classification:
* Gene or point (change of molecular structure of genes, occurring doe to replacement, insertions or deletions of nucleotides);
* Chromosomal (structural changes of chromosomes, appearing due to translocation or deletion of chromosomes, significant on the extension of parts);
* Genome (changes in the numbers of chromosomes).
Mutagenesis – incorporating changes in nucleotide sequence of DNA (mutations). Two types of mutagenesis are: Natural (spontaneous) & artificial (induced) mutagenesis.
Natural or spontaneous mutagenesis occurs due to the influence of mutagenic factors of environment such as UV, radiation & chemical mutagens on the genetic material of living organisms.
Artificial mutagenesis is widely used for studying proteins & improving their properties (directional evolution).
Changes with specific probability are incorporated into the DNA sequence using the non-directional mutagenesis method. Various chemical & physical influences - mutagen substances, UV& radiation can be mutagenic factors (mutagens). Screening & selection o those, which satisfy the mutagenesis purpose, are done after obtaining mutant organisms. Non-directional mutagenesis is more labor-consuming & carrying it out is justified if effective mutant screening system is developed.
Changes are incorporated in DNA in much earlier known site in directional (site-specific) mutagenesis. For this purpose, carry out synthesis of short single-stranded molecules of DNA (primers), complementary target DNA except the mutation place.
Uridine matrix, i.e same molecule in which the remains of thymine are replaced with uracil, is obtained for bacterial plasmids (extra chromosomal circular DNA). Primer is annealed on matrix & carry out completion of it into vitro with the help of polymerases upto circular DNA, complementary uridine matrix. Bacterial cells are transformed by two-stranded hybrid DNA & uridine matrix inside the cells is broken into foreign & second strand is completed on mutant single-stranded circular DNA. Efficiency of such mutagenesis method is less than 100 %.
PCR allows in carrying out site-directed mutagenesis with the use of pair of primers, carrying mutation & also random mutagenesis. In the last case, mistakes in 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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