The thick and thin filaments of the indirect flight muscles of homozygous animals appear normal at eclosion. In flies more than 2 days old, the fibres show a partial hypercontraction phenotype (fibres are pulled at the posterior end).

Heterozygotes rarely exhibit free myofibril fibres and if present they are cut, fragmented, torn and gapped. Indirect flight muscle fibres are disrupted in homozygotes and heterozygotes.