The myofibrils of heterozygotes show striated fibres with a tendency to fray.

Myofibrillar bundles of thick and thin filaments are present but lack Z-discs and all sarcomere repeats. Aberrant Z-discs are seen as dense filament bundles in the myofibril at pupal stages and move to the periphery of the fibrils at adult stages. The mutant actin can bind myosin as seen by comparing the kinetics of force generation of wild type actin. The absence of Z-discs, α-actinin and 2 high molecular weight proteins suggest that the substitution at residue 93 affects the binding of mutant actin to a protein which is necessary for Z-disc assembly or maintenance.