Haploid and diploid yeast cell strains of Saccharomyces cerevisiae were labeled with$[6\text{-}{}^{3}{\rm H}]\text{uracil}$, a general precursor of nucleic acids. Damage from tritium decay was accumulated at 4°C. Tritium-induced reproductive death, gene conversion, and mutation were compared to the same effects produced by gamma radiation. In all cases, the results were qualitatively similar to gamma rays, suggesting that the genetic hazard from incorporated environmental tritium in eucaryotic cells is similar to an equivalent dose of X rays. The most sensitive genetic assay for the effects of tritium decay in diploid yeast is the induction of genetic recombination. This induction of genetic recombination also occurs during normal growth of cells at 30°C at total activities of as little as 1 μCi/ml. Therefore, many experiments, using small amounts of tritium precursors, may be affected by tritium-induced genetic recombination. This effect of tritium should be considered in experimental designs, using tritium isotopes.

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