Transposon tagging (1 ) is a method for the isolation of genes, which display a mutant phenotype, Mutants that contain the transposon insert are “tagged” with the transposon and often display the characteristic chimeric or variegated phenotype owmg to transposase-medtated excision. With the help of the transposon sequences, the mutant allele and then the corresponding wild type gene can be isolated (2 )