| Summary: | Genetic change in meiotic cells of Saccharomyces cerevisiae was examined for comparison to pre-existing mitotic data. The response of meiotic cells to various chemicals indicated that sporulation may be inhibited without a total inhibition of meiotic recombination, but no evidence for the induction of increased meiotic gene conversion above spontaneous levels at ~trp 5, in the strain D7, was found. However, in experiments where meiotic cells were treated before a return to mitotic growth the frequency of coloured colonies were enhanced above spontaneous levels. The coloured colonies were attributed mainly to reciprocal recombination between ads 2 and its centromere and further work will be required to establish whether this reflects a difference between recombination for these different loci, or else a difference between gene conversion and reciprocal recombination. A "meiotic effect" associated with the time of initiation of meiotic DNA synthesis was also found after the treatment of meiotic cells with ethidium bromide, which blocked meiotic recombination and meiotic DNA synthesis, but resulted in no lethality in mitotic cells. Further, it was demonstrated that in untreated cultures the mitochondrial DNA replicated synchronously with the nuclear DNA. Modification of the response of meiotic cells in comparison to mitotic cells was also found for N-methyl-N'-nitro-N-nitrosoguanidine induced mutation and sensitivity to the lethal effects of X-rays and ultraviolet light. In the case of N-methyl-N'-nitro-N-nitrosoguanidine no enhanced mutagenic activity was found during meiotic DNA synthesis unlike during mitotic DNA synthesis which may be due to an absence of enhanced reactivity of the DNA during meiotic DNA synthesis, while cells prior to meiotic DNA synthesis appeared more resistant to the lethal effects of X-rays and ultraviolet light than cells prior to mitotic DNA synthesis. These findings indicate differences do exist between the sensitivities of meiotic cells and mitotic cells of Saccharomyces cerevisiae.
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