Cyclic variations in sensitivity to X-irradiation during meiosis in Saccharomyces cerevisiae.

Cyclic variation in mutation induction and lethality was found following X-irradiation during meiosis in Saccharomyces cerevisiae. An enhanced mutagenic response was found in meiotic G1 phase cells in comparison to cells later in meiosis, similar to the response shown during mitosis, but meiotic G1 phase cells appeared more resistant to the lethal effects of X-irradiation than mitotic G1 phase cells. Resistance to the lethal effects of X-rays was found during meiotic DNA synthesis in the strain SK1, which may indicate the operation of a sister-chromatid exchange repair mechanism. A difference was found between gene conversion which appeared to be at a maximum by the end of meiotic DNA synthesis and reciprocal recombination, which could be induced up to prophase I.