[Relative competitiveness of haploid and diploid yeast cells growing in a mixed population]

Saccharomyces cerevisiae was grown in a rich medium under the conditions of "quasi-continuous" cultivation and, after 200-300 generations, its diploid cells almost completely displaced haploid cells from the original mixed "haploid-diploid" population where the ratio between diploid and haploid strains was either 1:1 or 1:100. The cultivation at 40 degrees C did not change the relative competitive ability of haploids and diploids. When cells were cultivated in a rich medium at 6 degrees C or in a minimal medium at 30 degrees C, none of the strains showed an advantage over others for about 200 generations. Haploid cells had an advantage over diploid cells during "quasi-continuous" growth in the minimal medium at 30 degrees C. When the temperature was elevated to 40 degrees C, diploid cells displaced haploid cells from the mixed population. No advantage was found for diploid or haploid cells grown in a medium with an elevated KCl content (1.5 M). Haploid cells had an advantage over diploid cells when Pichia pinus was cultivated in a minimal medium. The results are discussed using the hypothesis about the diploid phase being fixed in the course of biological evolution.