Comparison of dominant lethal and heritable translocation methodologies

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Groups of male Alderly Park mice of proven fertility were dosed by gavage for 5 consecutive days per week for 8 weeks or 5 consecutive days only with 100 or 150 mg/kg bodyweight ethyl methanesulphonate (EMS) or by intraperitoneal injection once a week for 8 weeks or once only with 500 mg/kg shikimic acid. Animals dosed in this manner were compared in the dominant lethal and heritable translocation assays. Animals were mated for 2 consecutive weeks following the 8-weak treatment and for 8 consecutive weeks after the 1-week treatment: regimes which were thus non-specific and specific respectively for the stages of spermatogenesis. An additional method of measuring dominant lethality involving counting uterine scars after weaning (Soares (1972) Mutation Res., 16, 425–427) was used and also compared with the conventional method. EMS was clearly confirmed as a mutagen but this was not the case for shikimic acid. For screening purposes the dominant lethal 8-week mating assay was much more efficient in return for the same effort for detecting mutagenic responses than an 8-week mating heritable translocation assay, since the induction of dominant lethal effects paralleled the induction of heritable translocations. 8-week treatment with EMS showed increased dominant lethality but severely reduced fertility and the small numbers of male offspring born made potential heritable effects difficult to assess. The 1-week treatment with EMS produced both dominant lethal and heritable effects. Soares' method can be useful for determining determinant lethal effects in a heritable translocation assay. The “sieving” method of mating to determine partial and total sterility questions the necessity for a negative control in a heritable translocation study.