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mutagenesis
Mutagenesis is a process by which the genetic information of an organism is changed in a stable manner, resulting in a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using laboratory procedures. In nature mutagenesis can lead to cancer and various heritable diseases, but it is also a driving force of evolution. Mutagenesis as a science was developed based on work done by Hermann Muller, Charlotte Auerbach and J. M. Robson in the first half of the 20th century.
==Background==
DNA may be modified, either naturally or artificially, by a number of physical, chemical and biological agents, resulting in mutations. In 1927, Hermann Muller first demonstrated that mutation with observable changes in the chromosomes can be caused by irradiating fruit flies with X-ray, and lent support to the idea of mutation as the cause of cancer. His contemporary Lewis Stadler also showed the mutational effect of X-ray on barley in 1928, and ultraviolet (UV) radiation on maize in 1936. In 1940s, Charlotte Auerbach and J. M. Robson, found that mustard gas can also cause mutations in fruit flies.
While changes to the chromosome caused by X-ray and mustard gas were readily observable to the early researchers, other changes to the DNA induced by other mutagens were not so easily observable, and the mechanism may be complex and takes longer to unravel. For example, soot was suggested to be a cause of cancer as early as 1775, and coal tar was demonstrated to cause cancer in 1915. The chemicals involved in both were later shown to be polycyclic aromatic hydrocarbons (PAH). PAHs by themselves are not carcinogenic, and it was proposed in 1950 that the carcinogenic forms of PAHs are the oxides produced as metabolites from cellular processes. The metabolic process was identified in 1960s as catalysis by cytochrome P450 which produces reactive species that can interact with the DNA to form adducts, the mechanism by which the PAH adducts give rise to mutation however is still under investigation.
Mammalian nuclear DNA may sustain more than 60,000 damages per cell per day, as listed with references in DNA damage (naturally occurring). If left uncorrected, these adducts, after misreplication past the damaged sites, can give rise to mutations. In nature, the mutations that arise may be beneficial or deleterious — it is the driving force of evolution, an organism may acquire new traits through genetic mutation, but mutation may also result in impaired function of the genes, and in severe cases, causing the death of the organism. In the laboratory, however, mutagenesis is a useful technique for generating mutations that allows the functions of genes and gene products to be examined in detail, producing proteins with improved characteristics or novel function, as well as mutant strains with useful properties. Initially the ability of radiation and chemical mutagens to cause mutation was exploited to generate random mutations, but later techniques were developed to introduce specific mutations.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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