Spontaneous mutation

At this point, it may be interesting to indicate that the fact that the G-C pairs constitute the unstable part of the genome and that they mutate spontaneously more frequently than the A-T pairs has been reported in a number of publications.180-182 One cannot and should not, however, conclude from this situation that miscouplings through tautomerization of bases are the principal cause of spontaneous mutations, because those are definitely known to be due to a large series of causes, the relative importance of which is difficult to ascertain. The concordance between the theoretical predictions and the experimental facts is, however, worthwhile stressing, as an eventual discordance would certainly have been by some. 

The health consequence of deleterious mutation in populations is poorly understood, despite the large effort that has been expended in the study of mutation. Spontaneous-mutation rates are known only roughly, the forces that maintain or alter gene frequencies in populations are not well understood, and the relative impacts of different types of mutations are obscure. 

Mutagenlzed seed of thallana gives rise to Ml plants chimeric for a large number of heterozygous mutations. Spontaneous... 

When dealing with pleiotropic respiratory-deficient mutants of yeast, three practical difficulties constantly arise. The major inconvenience is the general genetic instability of the chromosomal pleiotropic respiratory-deficient mutants in S. cerevisiae where an additional p mutation spontaneously arises with very high frequency Since both the nuclear and the mitochondrial mutations are often expressed by deficient cytochromes aas and b, as well as by the loss of oligomycin sensitivity of the ATPase, the biochemical study of these double mutants is very difficult. An easy way out of this difficulty is to use chromosomal respiratory-deficient mutants of a petite-negative yeast species like 5. pombe, where no viable p mutation can be induced. 

The choice of the strain of microorganism is one of the important variables in the process. The strains to be used in manufacture are mutants of the original producer, which are chosen as the result of a planned program of mutant selection. Sometimes a spontaneous mutation occurs usually, it is induced by mutagenic agents or irradiation of various sorts. The choice of the best strain depends on its abiUty to produce large amounts of the proper antibiotic in a reasonable time from ingredients that are economically feasible (73). 

False. Continuous cultures operate for lengthy periods. Spontaneous mutations will arise and if they can compete successfully with the parent organism (by virtue of higher growth rate) they can predominate in the culture. Batch cultures have short growth times and so do not suffer such drawbacks. 

LRP4 is another receptor of the LDL receptor gene family involved in regulation of embryonic patterning, mainly controlling formation of limb structures. Loss of receptor activity in gene targeted mice or spontaneous mutation in bovine cause abnormal limb development and... 

PTEN Cowden disease, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome, Lhermitte-Duclos disease overgrowths of various organs, hamartomas of the skin, mucosa, cerebellar cortex high risk of developing several types of cancer. Spontaneous pten mutations found frequently in human cancers... 

The biflagellate unicellular green alga Chlamydomonas reinhardtii is prone to spontaneous mutations that produce deficiencies in flagellar proteins and MT assembly, substructure, and function. Viable mutants that are either nonmotile or slow moving can be isolated and analyzed biochemically and morphologically, thereby establishing structure-function correlations. Electron microscopic analysis... 

Some established cell lines were derived from malignant tissue. Many of these cell lines can form tumors when injected into susceptible animals. Other established cell lines are not Uunorigenic. However, exposure to carcinogens, and irradiation can cause these cells to form tumors in susceptible animals. In addition, transformation can be caused by spontaneous mutations, by growth factors, and by viral (or oncogenic) transformation (Table 6). Malignant transformation is defined as consisting of the series of events that cause normal cells to develop the capacity to form tumors. 

Rephcation errors, even with a very efficient repair system, lead to the accumulation of mutations. A human has 10 nucleated cells each with 3 X 10 base pairs of DNA. If about 10 cell divisions occur in a lifetime and 10 mutations per base pair per cell generation escape repair, there may evenmaUy be as many as one mutation per 10 bp in the genome. Formnately, most of these will probably occur in DNA that does not encode proteins or will not affect the function of encoded proteins and so are of no consequence. In addition, spontaneous and chemically induced damage to DNA must be repaired. 

Mutations resulting in ethambutol resistance can arise spontaneously. The exact changes are unknown but may involve enzymes in carbohydrate synthesis pathways. 

Hall BG (1990) Spontaneous point mutations that occur more often when advantageous than when neutral. Genetics 126 5-16. 

Oiler, A.R. and Thilly, W.G. (1992). Mutational spectra in human jS-cells. Spontaneous, oxygen and hydrogen peroxide-induced mutations at the hprt gene. J. Mol. Biol. 228, 813-826. 

M3. Maeda, M., Bawle, E. V., Kulkami, R Beutler, E., and Yoshida, A., Molecular abnormality of a phosphoglycerate kinase variant generated by spontaneous mutation. Blood 79,2759-2762 (1992). 

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