A direct screen identifies new flight muscle mutants on the Drosophila second chromosome

An ethyl methanesulfonate mutagenesis of Drosophila melanogaster was undert aken, and >3000 mutagenized second chromosomes were generated. More than 80 0 homozygous viable lines were established, and adults were screened direct ly under polarized light for muscle defects. A total of 16 mutant strains i n which the indirect flight muscles were reduced in volume or disorganized or were otherwise abnormal were identified. These fell into seven recessive and one semidominant complementation groups. Five of these eight complemen tation groups, including the semidominant mutation, have been mapped using chromosomal deficiencies and meiotic recombination. Two complementation gro ups mapped close to the Myosin heavy chain gene, but they are shown to be i n different loci. Developmental analysis of three mutations showed that two of these are involved in the early stages of adult myogenesis while the ot her showed late defects. This is the first report of results from a systema tic and direct screen for recessive flight muscle defects. This mutant scre en identifies genes affecting the flight muscles, which are distinct from t hose identified when screening for flightlessness.