METHODOLOGICAL ASPECTS OF THE WHITE-IVORY ASSAY OF DROSOPHILA-MELANOGASTER

The white-ivory somatic assay of Drosophila melanogaster was developed to detect genotoxic agents which induce loss of a tandem duplication. Although the mechanism of this loss is not known, some suggestions po int to intrachromosomal recombination as the main reversion mechanism. Since the few papers published to date on this assay present controve rsial methodologies, prior to a larger study of chemicals with differe nt mechanisms of action, we have carried out an analysis to optimize s ome conditions of this assay. For this purpose, we have used three dif ferent strains and four well characterized mutagenic chemicals: N-ethy l-N-nitrosourea (ENU), methyl methanesulfonate (MMS), ethyl methanesul fonate (EMS) and hexamethyl phosphoramide (HMPA). The results obtained allow us to conclude that: (i) the best strain for this assay is C(1) DX,y,f/Dp(1:1:1:1)w(i),y(2), although the use of strain FM6,l(1)(66a)/ Dp(1:1:1:1)w(i),y(2);st/st could be considered for some mechanistical studies; (ii) developmental reasons make it necessary to use as estima te of reversion frequency the proportion of eyes showing at least one spot; (iii) reversion frequency cannot be used as estimate of mutation efficiency, neither can spot size evaluate time of spot induction; (i v) the four chemicals clearly induce loss of the w(i) duplication; acc ording to their activities they rank ENU > HMPA > MMS approximate to E MS.