The dependence of radiation-induced genetic instability on yeast cell ploidy

The data for the survival and the delayed appearance of colonies by isogenic haploid and diploid yeasts Saccharomyces cerevisiae of wild-type and homozygous radiosensitive mutants surviving radiation exposure are presented. The delayed appearance of colonies by irradiated cells is regarded as one of the genetic instability features. An original data showing a well-defined genetic instability for radiosensitive diploid mutants with exponential survival curves has been obtained. In spite of defects in the repair of DNA double-strand breaks diploid, but not haploid mutants, inherit some sub-lesion resulting in genetic instability. Therefore, the effect of the late appearance of colonies by irradiated diploid yeast cells is not related uniquely to the shape of the survival curve and with the cell ability to recover from the double-strand DNA breaks. It is concluded that radiation-induced genetic instability is determined by cell ploidy rather than the sigmoid shape of the survival curve and the ability of cells to recover from radiation damage as it has traditionally assumed for yeast cells.