The delayed appearance of haploid and homozygous diploid Saccharomyces cerevisiae yeast cells of wild-type and radiosensitive mutants surviving after exposure to gamma rays and alpha particles

The aim of this paper is experimental investigations of the delayed appearance of haploid and homozygous diploid Saccharomyces cerevisiae yeast cells of wild-type and radiosensitive mutants surviving after exposure to gamma rays and alpha particles. Delayed appearance of colonies exemplifying genetic instability are presented for cells surviving after radiation exposure to 60Co γ-rays and 239Pu α-particles. Relative biological effectiveness (RBE) of densely ionizing radiation was shown to be practically identical both for cell survival and the delayed appearance of clones. The RBE values are determined by cell ability to recover from radiation damage. These findings are not new for cell survival, while they are fundamentally new for genetic instability. The degree of genetic instability is mainly determined by cell ploidy: both resistant and radiosensitive diploid strains in contrast to haploids demonstrate large extent of the delayed appearance of clones surviving after irradiation (100% vs. 20%). The primary conclusion may be formulated as follows: the delayed appearance of clones by cells surviving after radiation is mainly determined by cell ploidy rather than the sigmoidal shape of survival curve and ability of cells to recover from radiation damage as it is traditionally assumed for Saccharomyces cerevisiae yeast cells. It may be expected that the genetic instability would be more expressed for diploid somatic cells than for haploid sex cells if these patterns can be retained for the higher eukaryotes also.