Null mutations of glass remove photoreceptor cells
in all of the three organs in which they occur. The mutants
have compound eyes that are reduced in size and elliptical or
diamond shaped; the texture is glassy from fused facets and
irregular surface. Ocelli are flattened and lack pigment;
there is no ocellar neuropil (Moses et al., 1989). In larvae,
the visual Bolwig organs are absent in gl2, but present in
gl3. Neither mutant expresses chaoptin (Moses et al., 1989).
Color of compound eyes and Malpighian-tubules variably reduced
depending on allele. In the presence of the dimorphic sex-linked modifier, msd(gl)d, males have more pigment than
females, whereas males have the same eye color as females when
they carry the monomorphic allele msd(gl)m [Birchler, 1984,
Genet. Res. 44: 125-32]. dsx homozygotes of either X constitution but especially XX produce more pigment than dsx+ (Smith
and Lucchesi, 1969, Genetics 61: 607-18); however msd(gl) was
not controlled by Smith and Lucchesi. Pigmentation increases
with increased developmental temperature. At high or very low
levels of pigment production the sexual dimorphism disappears.
Weak alleles have small smooth eyes and normal pigment levels
in both sexes. Mild alleles have eyes reduced to two-thirds
normal size and approximately 20% normal eye-pigment levels
and male levels approximately 2X female levels. Moderate
alleles reduce eye size to half normal and pigment to about 5%
normal levels with male levels approximately 3X those of
females. Strong alleles have eye area less than half normal,
and eyes are virtually colorless in both sexes (Smith and
Lucchesi). The optic lamina is virtually nonexistent and the
medulla is very small and disorganized in gl1; the lamina and
medulla are both small and disorganized in gl2 and gl3 [Meyerowitz and Kankel, 1978, Dev. Biol. 62: 112-42 (fig.)].
Mosaic studies using gl3 show that the gl genotype of the eye,
rather than that of the optic lobe, determines the axon array
of the optic lobe (Meyerowitz and Kankel, 1978). Structures
of individual neurons studied by S.H. Garen and Kankel (1983,
Dev. Biol. 96: 445-56). Retinula cells of the mutant are
irregular and rhabdomeres are lacking; the electroretinogram
shows no response to light (Pak, Grossfield and White, 1969).
gl flies are nonphototactic and males exhibit depressed courtship activity [Merrell and Underhill, 1956, Genetics
41: 469-85; Hall, Tomkins, Kyriacou, Siegal, Von Schilcher
and Greenspan, 1980, Developmental Neurobiology of Drosophila
(Siddiqi, Babu Hall and Hall, eds.). Plenum Press, New York,
pp. 425-56]. Wing beat frequency increased (Williams and
Reed, 1944, Am. Nat. 78: 214-23).
No ERG or deep pseudopupal in none/none flies. In
the compound eye, corneal facets are fused and corneal hairs
displaced, but corneal nipples are present. There is an all-glial cell mass in the peripheral retina and there are no
rhabdomeres or optic cartridges as in the wild-type fly. In
the ocellar area, only remnants of the ocellar lenslets can be
observed.
