Homozygotes and ss^aB/ss^aP88 flies show transformation of the arista to distal mesothoracic tarsus. Expressivity of the phenotype is higher in ss^aB/ss^aP88 flies than in ss^aB homozygotes. The expressivity of the phenotype decreases with increasing temperature in ss^aB/ss^a, ss^aB/ss^ax, ss^aB/ss^aP88 or ss^aB/ss^a40a flies. Homozygous or ss^aB/ss^aP88 flies do not generally produce an ectopic tarsal response to chemical stimulation. Homozygous and ss^aB/ss^aP88 flies can sometimes fly.

Bristles of female like a slight Minute, especially postscutellars. At 25^oC, aristae inconspicuously thickened at base, plumed or threadlike for rest of extent. At 18^oC penetrance is 7% and expression weak; at 14^oC, ss^aB enhanced and resembles ss^a; al causes reduction of ss^aB arista at 25^oC but has no effect on transformed arista at 14^oC (Villee, 1943). Legs frequently have lumps at second joint of tarsi; more pronounced in male and result in doubling of sex combs, which are strung along first and second fused joints. Eyes a little flattened. Except at low temperatures, all characters slight and may overlap wild type. ss^aB/ss¹ has slight Minute phenotype but wild-type legs and aristae. ss^aB/ss^aSp like ss^aSp with large tarsal aristae. RK2. Struhl (198) and Posakony. weak allele cold-sensitive