[The proof of real increase in the frequency of reverse mutations in haploid yeasts in media with decreased adenine content].

It has been shown by the direct experiment in the haploid yeast Saccharomyces cerevisiae, strain p192 (a ade2-192), that, if cultivated in the solid media containing 1 and 10 mg/l of adenine, the reversion frequencies (5.6 X 10(-8) and 0.82 X 10(-8), respectively) do not depend on the number of cells (from 10(2) to 10(7)) in colonies growing on either medium. This means that the difference in the reversion frequencies mentioned is not connected with the "selection effect" and is only caused by the varying initial content of adenine in the medium. A method combining the technique of ordered plating and the use of nuclear filters is recommended for the study of mutagenesis in microorganisms.