Evidence for Two Types of X-Ray-Induced Lethal Damage in Saccharomyces cerevisiae

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Abstract
Cells of two complementary mating type haploid strains of the yeast Saccharomyces cerevisiae were paired by micromanipula-tion and zygote formation and viability were studied. Irradiation of one of the cells before pairing did not affect conjugation, but the diploid zygote formed showed many evidences of radiation damage including delay of division, abnormal divisions, swelling, and death. The percentage of inviable zygotes increased with dose in a multiple-hit fashion. Doses lethal to 99.9% of the haploid cells reduced the zygote survival to about 50%. The results were interpreted in terms of recessive and dominant lethal damage.