Heterozygous flies have very short and highly branched arista laterals. The decreased length of the laterals is associated with a decreased rate of elongation and premature cessation of elongation. There is no delay in lateral outgrowth. Initially a single lateral is formed, but it is thicker than normal and sometimes individual bundles of actin filaments can be seen. The laterals split near the distal tip as they elongate and at later stages they appear to be split over more of their length. The shape of the laterals in cross section is often irregular, in contrast to the circular wild-type laterals. The actin bundles are irregular in shape and extend further into the centre of the lateral than normal, although most are still associated with the plasma membrane. The actin filaments occupy more of the lateral cross section than normal, although they appear less tightly packed than wild type. The density of microtubules is significantly reduced and their distribution is more irregular compared to wild type.

Bsb², Sb[+]/Sb¹ has visible | dominant phenotype

Bsb², Sb[+]/Sb¹ has ocellar bristle phenotype