32 Neffgen, Anna Klinner, Ulrich 100000 Publikationsserver der RWTH Aachen University Aachen German IV, 135 S. : Ill., graph. Darst. It was the aim of this work to design and validate a test system, which makes it possible to recognize mutagenic and recombinogenic effects. The system consists of two S. cerevisiae strains. In the haploid strain HAN alpha ura3(disrupted) trp1(disrupted) ADE2::URA3::kanMX4 the URA3 gene and the kanMX4 cassette were inserted on chromosome XV distal to the ADE2 locus. On chromosome XV the diploid strain DAN alpha/alpha ura3(disrupted)/ura3(disrupted) trp1(disrupted)/trp1(disrupted) PHO80/pho80::TRP1 ade2-101/ADE2::URA3::kanMX4 contains the same construction as the strain HAN. The TRP1 gene is inserted into the PHO80 locus, which is next to the centromere on the other arm of the homologue of chromosome XV. The two strains were designed by series of targeted mutations and by fusion of the protoplasts. The genotype was verified by molecular-genetic methods. The use of the antibiotic resistance and the counterselective markers URA3-ura3 and TRP1-trp1 makes the direct quantitative registration of different genetic events possible. With the help of the URA3 gene in the strain HAN forward mutations can be detected. The close coupling of the URA3 gene with the ADE2 locus and the kanMX4 cassette makes it possible to detect beside point mutations also more spacious sequence changes such as deletion, insertion or inversion. In the diploid strain DAN the determination of the total number of uracil auxotrophs allows the simultaneous registration of mutations, mitotic gene conversions, crossing over events as well as chromosome losses. The frequency of mitotic recombination events is determined by the calculation of the difference between this total number and the mutation frequency in the strain HAN. The selection of tryptophan auxotrophes supplements the assessment of the chromosome losses. The close coupling between the ADE2, URA3, and kanMX4 loci in the strain DAN allows a phenotypic differentiation of gene conversions according to their length, between short (SGCs), medium (MGCs) and long (LGCs) events. The homocygoticity of the mating type it prevents the falsification of the results by meiotic recombination events. Using the strain system, the frequency of spontaneous mutations and recombination events was as had been expected. Deviations concerned the frequency of gene conversions and crossing over events in the strain DAN. They occurred less frequently than in some other yeast test systems. A cause for this can be the homocygote configuration of the mating type alleles. Validating the test system with substances with well-known effect provided the expected results. MNNG and UV-radiation led mainly to the increase of the mutation frequency. To a smaller extent frequencies were induced by gene conversions and crossing over events. An effect caused by ethidiumbromide or benomyl could not be proven under the incubation conditions, which had been chosen. A weak mutagenic and recombinogenic effect of aniline was observed. The HAN/DAN system is a test system, with which mutagenic and recombinogenic influences can be recognized within few days. Beyond that the genetic events can be characterized by applying phenotypic and molecular-biological methods. Further advantages of the test system developed in this work are its easy handling and its reasonable price as well as the possibility to identify potential danger materials in a sensitive way. Aachen, Techn. Hochsch., Diss., 2004 ; PUB:(DE-HGF)11, ; 2, ; Mutagenitätstest Rekombination Genetik Biotest Saccharomyces cerevisiae Dissertation / PhD Thesis 2005 RWTH-CONV-121585 2005 https://publications.rwth-aachen.de/record/59839