Flies homozygous or hemizygous for ac1 lack all four dorsocentral bristles. No phenotypes are seen in heterozygotes.
The total number of bristles on the basitarsi of the second legs is reduced. The number of bractless bristles on the basitarsi remains normal. Significantly more bristles are missing from the anterior side of the basitarsus than from the posterior side. One or the other of the distal sensilla is sometimes missing, and an ectopic sensillum sometimes forms proximally between bristle rows 3 and 4.
Posterior dorsocentral bristles missing; also posterior supra-alar and anterior vertical bristles frequently missing. Anterior dorsocentrals displaced anteriorly (FBrf0020635). Garcia-Bellido (FBrf0033191) finds anterior dorsocentral bristles more strongly decreased than posterior dorsocentrals. Hairs usually fewer near position of posterior dorsocentrals; interocellar hairs invariably fewer, typically absent. Eyes partly devoid of hairs. Trichomes unaffected. Limited nonautonomy near the borders of somatic spots with respect both to numbers and positions of bristles and hairs (FBrf0009297; FBrf0013897; FBrf0020635).