Lindsley & Grell, 1972, pp. 22-23
origin: Spontaneous in a female.
discoverer: Tice, l3b.
references: 1914, Biol. Bull. 26: 221-30 (fig.).
Morgan and Bridges, 1916, Carnegie Inst. Wash. Publ. No. 237: 66 (fig.). Morgan, Bridges, and Sturtevant, 1925, Bibliog. Genet. 2: 29-33.
phenotype: Eye restricted to narrow vertical bar of about 90 facets in the male and 70 facets in the female as contrasted with normal numbers of about 740 for males and 780 for females [Sturtevant, 1925, Genetics 10: 117-47 (fig)]. Homozygous female fully viable. B/+ female has about 360 facets and shows indentation terminating in horizontal fissure on anterior margin of eye, producing a kidney-shaped eye. B/B and B/+ completely separable from wild type, but in some genetic backgrounds B/B overlaps B/+ slightly. Classifiable in single dose in triploids by slight anterior nick in eye (Schultz, 1934, DIS l: 55); is useful in the recognition of triploids. Eyes of female heterozygous for a deficiency for B and a normal X are normal (Sutton, 1943, Genetics 28: 97-107). Log of facet number inversely proportional to temperature of development (Hersh, 1930, J. Exptl. Zool. 57: 283-306). Bi (infrabar): less reduction in eye than B.
Nonautonomous over short distances (Sturtevant, 1932, Proc. Intern. Congr. Genet., 6th, Vol. 1: 304-7). Facet development enhanced in organ culture by addition of wild type cephalic complexes [Kuroda and Yamaguchi, 1956, Japan J. Genet. 31: 97-102 (fig.)]. Facet number can be increased by addition of a number of compounds to the medium; probably not a specifie inhibition of effect of B (see work of Chevais, Khouvine, Kaji, Abd-E1-Wahab, and DeMarinis).
Embryological studies [Chen, 1929, J. Morphol. 47: 135-99 (fig.); Steinberg, 1941, Genetics 26: 325-46 (fig.); 1942, Genetics 27: 171-72; Power, 1942, Genetics 27: 161. DeMarinis, 1952, Genetics 37: 75-89 (fig.)] indicate that phenotype results from reduced number of cells in optic disk and reduced rate of cell division in anterior part of eye. Facet development responds strongly to environmental factors around 60 hr after oviposition (Luce, Quastler, and Chase, 1951, Genetics 36: 488-99). Pigmented but nonfaceted part of eye shows retinulae and dioptic apparatus lacking, but rudimentary ommatidia present, consisting of hypertrophied accessory cells (Wolsky and Huxley, 1936, Proc. Zool. Soc. London 485-89). RK1A.
cytology: Located in 16A1-2. Associated with Dp(1;1)B = Dp(1;1)15F9-16A1;16A7-B1.
other information: Since B is a tandem duplication, B homozygotes may give rise to a nonduplicated chromosome (reversal to normal phenotype) and a triplicated chromosome (i.e., double Bar = BB) as reciprocal products of unequal crossing over (Sturtevant and Morgan, 1923, Science 57: 746-47). From successive unequal crossovers in attached X's, Rapoport (1940, Zh. Obshch. Biol. 1: 235-70; 1941, DIS 15: 36-37) has been able to accumulate as many as 7 or 9 Bar regions in a single chromosome. Bar is the first recorded instance of position effect. Presumably results from the new band association 16A7-16A1 and can he reversed by rearrangements that separate these bands. Also the first case of cis-trans position effect, two 16A7-16A1 associations in the same chromosome producing greater facet reduction than two associations in homologous chromosomes; e.g., facet number in B/B is greater than in BB/+ (Sturtevant, 1925).
color figure: P. A. Otto (original)
b & w figure: Sturtevant and Beadle, 1939, An Introduction to Genetics, Saunders, Philadelphia (original drawn by Edith M. Wallace)
photograph: P. A. Otto (original)