The construction of the first balancer chromosome for the Mediterranean fruit fly, Ceratitis capitata

The construction of the first balancer chromosome: FiM1, for the medfly Cer atitis capitata is described. This chromosome has three overlapping pericen tric inversions and is marked with dominant and recessive mutations. The in version breakpoints of FiM1 suppress recombination throughout the length of the fifth chromosome, allowing lethal mutations to be recovered and mainta ined. This chromosome will provide a powerful tool for the manipulation of laboratory stocks, in particular, the recovery of new mutant and transgenic strains. We demonstrate the use of FiM1 for the recovery and maintenance o f chromosomes carrying lethal mutations.