Homozygous embryos have defects in myoblast fusion.

Paired vesicles are present at wild type levels and disappear as in wild type. However, the plasma membrane never vesiculates, instead extensive electron-dense plaques are present along apposed plasma membranes between pairs of myoblasts during stage 13. By stage 14 electron dense plaques have disappeared, groups of myoblasts are aligned in the same positions as mature myotubes but the membranes have failed to fuse.

Dorsal vessel and visceral mesoderm is unaffected but major distortions occur in somatic mesoderm. Strong allele: Late stages of embryonic development show mostly unfused myoblasts. First distortions are visible during germ-band retraction. Unfused myoblasts are often arranged in specific locations where in the wild type ventral, pleural and longitudinal muscles form.