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K Wöhrmann

Publications and source records attributed to K Wöhrmann.

6 recordsLinked to original sources
PubMed1991

[Contribution to the discussion on the release of transgenic organisms. II. Ecologic aspects].

Problems which might be caused by the release of transgenic organisms are discussed from the viewpoint of genetics, population genetics and ecology. On this background, the differences between "classical" methods to recombine genetic information and the more recent ones of gene engineering are pointed out and the predictability of gene interactions is discussed. Moreover, the possibility of uncontrolled reproduction of released transgenic organisms and the distribution of manipulated genes are demonstrated on the basis of our knowledge on nontransgenic organisms. Finally, the problems of risk assessment are emphasized.

Ecology↗
PubMed1991

[Contribution by discussion on the release of transgenic organisms. I. Genetic aspects].

Problems which might be caused by the release of transgenic organisms are discussed from the viewpoint of genetics, population genetics and ecology. On this background, the differences between "classical" methods to recombine genetic information and the more recent ones of gene engineering are pointed out and the predictability of gene interactions is discussed. Moreover, the possibility of uncontrolled reproduction of released transgenic organisms and the distribution of manipulated genes are demonstrated on the basis of our knowledge on nontransgenic organisms. Finally, the problems of risk assessment are emphasized.

Genetic Engineering↗
PubMed1987

Experimental evidence for the adaptive value of sexual reproduction.

It is generally believed that recombination by sexual reproduction is unfavourable in constant environments but is of adaptive value under changing environmental conditions. To test this theory, experimental populations of yeast (Saccharomyces cerevisiae) were set up and maintained at different levels of environmental heterogeneity. Recombination was estimated by determining sporulation rates. Sporulation rates first increased in populations living in highly variable environments, but after some time began to decrease. The decrease started last and was slowest in populations which were maintained under the same conditions for a sufficiently long time, to allow some adaptation of the gene pool to the respective environment. Patterns of genotypic variability could not be interpreted in such simple terms, but there was a statistically significant correlation between sporulation rate and genotypic variability. This correlation is to be expected because recombination generates genotypic variability. Summing up, recombination by sexual reproduction is advantageous in changing environments if the population can track the changes in the environment by changing its genotypic structure.

Alleles↗
PubMed1984

The effect of newly induced mutations on the fitness of genotypes and populations of yeast (Saccharomyces cerevisiae).

This paper analyses the fate of artificially induced mutations and their importance to the fitness of populations of the yeast, Saccharomyces cerevisiae, an increasingly important model organism in population genetics. Diploid strains, treated with UV and EMS, were cultured asexually for approximately 540 generations and under conditions where the asexual growth was interrupted by a sexual phase. Growth rates of 100 randomly sampled diploid clones were estimated at the beginning and at the end of the experiment. After the induction of sporulation the growth rates of 100 randomly sampled spores were measured. UV and EMS treatment decreases the average growth rate of the clones significantly but increases the variability in comparison to the untreated control. After selection over approximately 540 generations, variability in growth rates was reduced to that of the untreated control. No increase in mean population fitness was observed. However, the results show that after selection there still exists a large amount of hidden genetic variability in the populations which is revealed when the clones are cultivated in environments other than those in which selection took place. A sexual phase increased the reduction of the induced variability.

Ethyl Methanesulfonate↗
PubMed1977

Influence of defined gene blocks on the competitive ability of yeast genotypes.

Competition experiments were carried out under varying exogenic and endogenic conditions. The genotypes were marked by combinations of two esterase loci, each with two alleles. When genotypes of the line W7 were used, there was no demonstrable influence of the gene blocks marked by the Est-1 locus on the competitive ability at temperatures of 21 and 29 C. However, genotypes carrying the fast allele of the Est-2 locus were favored. At 38 C, the outcome of the competition was reversed. The defined gene blocks showed different effects when interacting with different genetic backgrounds (line M7). Genotypes marked by the slow allele of the Est-2 locus were now favored (21 and 29 C), and even the gene blocks marked by the alleles of the Est-1 locus influenced the genotypes' competitive abilities. Again, the results were partly reversed at 38 C. The results are discussed with regard to the importance of enzyme variants for the genotypic selection value.

Alleles↗