The microchaetae of Sb^sbd-VX1 mutants are shorter, fatter and straighter than in wild type. Further, Sb^sbd-VX1 microchaetae contain twice the number of actin bundles compared to wild type and these bundles are linked by more cross-bridges than in wild type. During development, these bristles grow more slowly than in wild type; the bristles therefore experience less constraint from the inner pupal case than wild-type bristles, which could account for the lack of curvature seen in the mutant bristles.

Longitudinal actin bundles in the bristle cells of Sb^sbd-VX1/Df(3R)sbd45 mutants exhibit a triangular cross-sectional profile that is larger than wild type. The filaments are packed hexagonally, like in wild type.

First difference from wild type evident at around 40 hours of pupal development, when the number of actin filament bundles becomes abruptly reduced, then disorganised at the tip accounting for the resulting frayed bristle ends.

phenotype more extreme when homozygous than when hemizygous; may not be null.