Dominant Lethality induced by X-Rays in Haploid and Diploid Saccharomyces cerevisiae

Abstract

IN a previous paper¹, evidence was presented for the presence of dominant lethals in X-irradiated haploid yeast cells. Diploid yeast zygotes formed by the conjugation of one irradiated and one un-irradiated haploid cell were found to exhibit signs of radiation damage, including swelling, delay in division and death. The damage responsible for inactivation of these half-irradiated zygotes was defined operationally as dominant lethal damage. The present communication describes a continuation of these experiments in which diploid cells homozygous for mating type were employed along with the two haploid cultures previously used. These diploid cells will conjugate with haploid or diploid cells of opposite mating type when placed in direct contact, thus permitting a similar determination of the frequency of dominant lethals in diploid cells. This was of interest because previous studies of the survival of X-irradiated yeast cells of higher ploidy² suggested that the frequency of this type of damage might increase with increasing ploidy.