Genes conversion

Using mitotic crossing-over as a test system has definite advantages. According to currently held views (see Holliday damage to the 

Mitotic intragenic recombination is mostly due to gene conversion, and it can be induced with a large variety of mutagens. A strain heteroallelic at loci ade2 and trp5, called D4, has been used to demonstrate genetic 

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S. cerevislae D7 Mitotic gene conversion No data + Yadav et al. 1982... 

Endosulfan is toxic to yeast but is also mutagenic without activation (Yadav et al. 1982). In vitro, endosulfan induced reverse mutations and mitotic gene conversion and increased the percentage of aberrant colonies in Saccharomyces cerevisiae but did not induce mitotic cross-overs (Yadav et al. 1982). 

Besides unequal crossover and transposition, a third mechanism can effect rapid changes in the genetic material. Similar sequences on homologous or nonhomol-ogous chromosomes may occasionally pair up and eliminate any mismatched sequences between them. This may lead to the accidental fixation of one variant or another throughout a family of repeated sequences and thereby homogenize the sequences of the members of repetitive DNA families. This latter process is referred to as gene conversion. 

Eukaryotic organisms Fungi Saccharomyces cerevisiae D7 Gene conversion Kochetal. 1988 ... 

Sharon D., Glusman G., Pilpel Y., Khen M., et al. (1999). Primate evolution of an olfactory receptor cluster diversification by gene conversion and recent emergence of pseudogenes. Genomics 61, 24-36. 

S. cerevisiae Gene conversion or mitotic recombination — — Fukunaga et al. 1982 Kharab and Singh 1985 Nestmann et al. 1979 Simmon 1979a... 

Brooks TM, Gonzalez LP, Calvert R, et al. 1985. The induction of mitotic gene conversion in the yeast Saccharomyces cerevisiae strain JD1. In Ashby J, de Serres FJ, et al., eds. Progress in mutation research. Vol. 5. Evaluation of short-term tests for carcinogens. Amsterdam, The Netherlands Elsevier Science Publishers, 225-228. 

Murthy MS Induction of gene conversion in diploid yeast by chemicals Correlation with mutagenic action and its relevance in geno-toxicity screening. Mutat Res 1979 64 1-17. 

Negative results for mutagenicity of d.v-chlordanc and tran.v-chlordanc were reported in various strains of bacteria and in hepatocyte cultures of small mammals. But technical chlordane proved mutagenic to selected strains of Salmonella typhimurium and induced gene conversions in certain strains of the yeast, Saccharomyces cervisiae (IARC 1979 USEPA 1980, 1988 WHO 1984). 

Mitotic gene conversion in Saccharomyces cerevisiae (August 1998)... 

Positive results from the Saccharomyces cerevisiae mitotic recombination assay indicate that a substance induces DNA recombination in this test system, i.e., mitotic gene conversion (within a gene) and/or mitotic crossing-over (between a gene and its centromere). 

The use of yeast cells as a eukaryotic complement to the Ames test led to the development of several protocols for the detection of mutation, gene conversion and recombination. The formal introduction of methods [23] followed by much development work from Zimmermarm s laboratory led to large systematic studies [24, 25] and OECD guidelines for the test battery (OECD 480, 481). However the assays are now rarely used, at least in part because of concerns over low sensitivity, thought to reflect limited permeability of the cell wall. 

Figure 19.4 Experimental procedure for the assessment of phototoxicity of formulations using the yeast assay. Formulations are spread on agar previously seeded by yeast cells. Photocytotoxicity is assessed by colonies counting after growth on complete medium, whereas genetically altered colonies (here gene conversion involving the t ptophan locus) are detected using selective growth medium (here tryptophan-free), [39].

Zimmermann, F.K., Kern, R. and Rasenberger, H.A. (1975) Yeast strain for simultaneous detection of induced mitotic crossing over, mitotic gene conversion and reverse mutation. Mutation Research, 28, 381-388. 

Singh I. 1984. Induction of gene conversion and reverse mutation by manganese sulphate and nickel sulphate in Saccharomyces cerevisiae. Mutat Res 137 47-49. 

Fortunately, a number of in situ, short-term bioassays to detect genotoxic and related effects have become available. These include a variety of measured endpoints such as aneuploids, chromosal aberrations, DNA damage, dominant lethal mutation, gene mutation, inhibition of intercellular communication, micronuclei, mitotic recombination and gene conversions, and sister chromatid exchange and cell transformation (IARC, 1989). A detailed discussion of these tests is beyond the scope of this book. However, such tests are important from our perspective as atmospheric chemists because, as we shall see, they can be used to detect biologically active compounds in very complex mixtures, and hence serve to focus chemical analysis efforts (IARC, 1989, p. 20). We emphasize in advance the... 

Saccharomyces cerevisiae, gene conversion - - 2000 Brooks etal. (1985)... 

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