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[en] Two Drosophila melanogaster stains were treated with independent and combined doses of ethylmethane sulfonate (EMS) and 60Co gamma radiation. The Columbia (CO3) and Riverside, California (RC1) strains were treated with three EMS doses (0.003; 0.006 and 0.12 M) or with four radiation doses (2.5, 5, 10 and 15 KR), or yet again with three combined doses of the two mutagens (0.002 M + 10 KR; 0.003 M + 5 KR and 0.004 M + 2.5 KR). Differences in sensitivity between the two stains were studied in terms of induction of sex-linked recessive lethal mutations, and the relationships between high mutagenic doses and frequency of induced mutation were determined. The relationship between EMS treatment and production of lethal mutations was distributed within a parabolic curve, a behavior due to selective elimination of the most sensitive cells from the point of view of mutability, or to the saturation of the ability to absorb the mutagen when administered at high doses. At the 0.006 M EMS dose, the percentage of lethal mutations obtained indicated the presence of resistence to this mutagen in the CO3 strain. With the combined EMS and radiation treatments, the CO3 strain showed a synergistic effect, while strain RC1 showed and additive effect. Previous data suggest that the CO3 strain has a more efficient repair mechanism since combined treatment seems to inhibit the repair enzymes. The CO3 strain is more affected by this type of inhibition. (Author)
[pt]
Duas linhagens de Drosophila melanogaster foram tratadas com doses independentes e conjuntas de etilmetanosulfonato (EMS) e radiacao gama de 60Co. As linhagens Columbia (CO3) e Riverside, California (RC1) foram tratadas com tres doses de EMS (0.003; 0.006 e 0.012 M), ou com quatro doses de radiacao (2.5; 5; 10 e 15 KR) ou, ainda, com tres doses conjuntas dos dois mutagenicos (0.002 M + 10 KR; 0.003 + 5 KR e 0.004 M + 2.5 KR). Foram estudadas diferencas de sensibilidade entre as duas linhagens, quanto a inducao de letais recessivos ligados ao sexo, e determinadas as relacoes existentes entre altas doses de mutagenico e frequencia da mutacao induzida. A relacao entre dose de EMS e producao de letais se distribuiu dentro de uma curva parabolica. Tal comportamento decorreu ou da eliminacao seletiva das celulas mais sensiveis sob o ponto de vista da mutabilidade, ou da saturacao na capacidade de absorcao do mutagenico, quando administrado em altas doses. Na dose de 0.006 M de EMS, a percentagem de letais obtida indicou a existencia, na linhagem CO3, de resistencia a acao deste mutagenico. No tratamento conjunto com EMS e radiacao, a linhagem Co3 apresentou um efeito sinergistico, enquanto a RC1 mostrou um efeito aditivo. Dados anteriores sugerem que a linhagem CO3 apresenta um mecanismo de reparo mais eficiente, ja que o tratamento conjunto parece inibir as enzimas de reparo, a linhagem CO3 e mais atingida por este tipo de inibicao. (Autor)Journal
Revista Brasileira de Genetica; ISSN 0100-8455; 
; v. 3(3); p. 251-264
; v. 3(3); p. 251-264