Essential protein that may function as a transcription regulator. Vital for pupal development. Required for proper development of the optic lobes and wings, and abdominal pigmentation.

(UniProt, Q24432)

Longitudinal veins fused at base of wing into bifid stalk. L3 delta-like at tip; L4 often incomplete at tip. Wing margins often excised at tip of L4. Wings spread in proportion to their shortness. High temperature enhances and low temperature produces overlapping of wild type. Stronger in male than in female. Hypomorphic allele; females heterozygous for bi and a deficiency for bi have outspread, crumpled, and very flimsy wings with an extreme bifid fusion of the basal regions of the longitudinal wing veins (Craymer and Roy, 1980, DIS 55: 204). Enhances Bx alleles as well as sd, cp, and vgnp (Waletzky). RK1.

Adults expressing omb1, the only allele studied in phenotypic detail, are impaired in optomotor turning responses in tests involving tethered or freely moving flies (Heisenberg et al., 1978; Blondeau and Heisenberg, 1982; Kulkarni, Steinlauf, and Hall, 1988, Genetics 118: 267-285; Dushay, Rosbash, and Hall, 1989, J. Biol. Rhythms 4: 1-27). The mutant is also aberrant in orientation to vertical stripe (Heisenberg et al., 1978). More detailed examination of "yaw torque" optomotor responses show that omb1 is restricted in responses to stimulation of "frontal visual field", with mutant behavior summarized as retaining "object responses" but missing "large field responses" (Bausenwein et al., 1986). The mutant is relatively normal in "lift/thrust" response to vertical pattern movement and in regard to landing response elicited by front-to-back horizontal motion. Slow phototaxis, using Y-tube, was markedly subnormal (Dushay et al., 1989). Giant arborizing fibers in lobula plate. Since isolation and the original histological examinations, anatomical abnormalities have become more pronounced, e.g., the optic lobes remain in "pre-imaginal" orientation in some omb adults, viz., long axis of medulla optic ganglia oriented more frontally than in wild-type (Blondeau and Heisenberg, 1982); other behavioral abnormalities: omb shows anomalous avoidance reaction, i.e., "antifixation" to objects in Y-maze test (Bulthoff, 1982, Biol. Cybernet. 45: 63-70); courting males exhibit diminished tracking responses of and turning responses to moving females (Cook, 1980, Biol. Cybernet. 37: 41-51; Tompkins, Gross, Hall, Gailey, and Siegel, 1982, Behav. Genet. 12: 295-307). Visual stimulus-induced metabolic activity in the optic lobes (monitored by distribution of radioactive 2-deoxyglucose) is normal, suggesting that basic structure and function of ganglia distal to lobula plate is normal (Bulthoff and Buchner, 1985, J. Comp. Physiol. 156: 25-34). Without effect on locomotor activity rhythm (Helfrich, 1986, J. Neurogenet. 3: 321-43).

Broad dark band on margins of all abdominal tergites, giving abdomen superficial appearance of uniform darkness. Viability of heterozygous female normal, of homozygous female < 10% normal, and of male 30% normal. Qd/Df(1)bi4 exhibit homozygous Qd phenotype as well as bi-like phenotype; Qd/bi and Qd/+ are normal with respect to bi (Banga, Bloomquist, Brodberg, Pye, Larrivee, Mason, Boyd, and Pak, 1986, Chromosoma 93: 341-46). RK2.