Isolation and characterization of flightless mutants in Drosophila melanogaster.

Since animal behaviour is executed through neuronal circuits including sensory receptors and muscle, genes vital for their development and differentiation must be found among mutants having behavioural anomaly. After mutagenesis with ethyl methanesulphonate (EMS), we screened for X-linked flightless mutants of Drosophila melanogaster by using column-type flight tester. Approximately 10(4) individuals were screened and 21 mutant genes were isolated. Chromosomal mapping and complementation experiments revealed that they belong to 15 cistrons randomly located on X chromosome, three cistrons having more than two alleles. Two of the isolated mutants (fltO2 and fltH, which are recessive both behaviourally and morphologically) were analysed with the mosaic fate mapping technique, and both were found to have their primary foci in mesodermal region of blastoderm, suggesting that the genes exert their primary effect in indirect flight muscle. Electronmicroscopic studies on the muscles from four alleles of the fltO2 cistron revealed an abnormality in myofibrillar arrangement. A possible deficit within Z-band components is discussed in relation to wings-up B mutants. The indirect flight muscle of flltH was also examined, and it was found that sarcomere length and diameter of myofibrils were abnormal. It was postulated that a possible factor which controls size of myofibrils is defective in this mutant. These examples indicate the advantage of combining ultrastructural examination with genetic mosaic mapping technique.