THE RELATIVE BIOLOGICAL EFFECTIVENESS OF ACCELERATED CARBON-IONS WITHDIFFERENT LET FOR INDUCING MITOTIC CROSSING-OVER AND INTRAGENIC REVERSION OF THE WHITE-IVORY ALLELE IN DROSOPHILA LARVAE

Purpose: To evaluate the relative biological effectiveness (RBE) of ac celerated carbon ions generated with a synchrotron for inducing mutati ons as a function of linear energy transfer (LET), using the loss of h eterozygosity for wing-hair mutations and the reversion of the mutant while-ivory eye-colour in Drosophila melanogaster. Materials and metho ds: The measurements were made using a combined mutation assay system so that induced mutant wing-hair clones as well as revertant eye-colou r clones can be detected simultaneously in the same fly. Larvae were i rradiated at the age of 72 +/- 6 h post-oviposition with X-rays or car bon ions with LET values of 13, 60 and 95 keV/mu m. Results: The RBE o f carbon ions for producing wing-hair mosaic spots increased with incr easing LET values. The RBE For the induction of eye-colour mutants did not change with LET. The estimated RBE values were found to be in the range 2 to 6.5 for the wing-hair and nearly unity for the eye-colour mosaic spot mutations. Conclusions: RBE-LET relationships were obtaine d for the induction of wing-hair and eye-colour mosaic spots. These re lationships suggest that more complex types of DNA damage, such as non -rejoinable strand breaks that increase with LET, may be responsible f or inducing the wing-hair mutation, while more simple forms of molecul ar damage induce reversion in the white ivory allele.