[Yeasts as an object for the detection and testing of mutagens. I. Estimation of mitotic crossing-over and the problems of a statistical evaluation of its frequency].

Spontaneous frequencies of the total mitotic segregation (ms) and mitotic crossing over (mco) in two strains of Saccharomyces cerevisiae, T1(RAD RAD) and T2(rad2 rad2) have been studied. 90 independent experiments were conducted for T1 and 75 for T2. We observed the following frequencies: 0.17 +/- 0.19% ms, T1; 0.30 +/- 0.034% ms, T2: 0.23 +/- 0.0055% mco, T1; 0.043 +/- 0.0142% mco, T2. The following experimental design is proposed for mutagen screening: at least three independent experiments for control and treatment, with 1000 or more colonies checked in every experiment. If the results of control as well as experimental sets are homogenous, then the Kastenbaum - Bowman test can be applied to evaluate the difference between control and treated groups.