Larval development 4 days longer than normal resulting in giant larvae, pupae, and imagos. Adult weight
1.7 times normal; increased size caused by increase in cell
size and not cell number [Simpson and Morata, 1980, Development and Neurobiology of Drosophila (Siddiqi, Babu, Hall and
Hall, eds.). Plenum Press, New York and London, pp. 129-40].
Pupariation delayed owing to delayed increase in ecdysteroid
titers; level reached at pupariation lower than normal; pupal
interval of normal length (Schwartz, Imberski, and Kelly,
1984, Dev. Biol. 103: 85-95). Not all genetically giant
flies show the giant character, the rest have normal size;
distribution sharply bimodal. Percentage giant greatest in
well-fed cultures, also raised by modifying action of bb11.
Penetrance of viable alleles enhanced in heterozygotes with
lethal alleles and deficiencies; viability decreased (Kaufman,
1972, Genetics 71: s28-29). Abnormalities in DNA metabolism
found in homo- or heteroallelic third instar gt females (Narachi and Boyd, 1985). Salivary gland chromosomes of double
thickness in some cells (Bridges, 1935, J. Heredity 26: 60-64). Feulgen staining shows extra round of DNA synthesis;
polytene chromosome can be analyzed in gt/Df larvae (Kaufman,
1972, Genetics 71: s28-29). Embryos carrying lethal giant
mutations have defects in the anterior and the posterior
domains (Petschek et al., 1987; Mohler et al., 1989). Posterior compartment of the labial segment deleted from blastoderm; cell death at germ-band elongation deletes anterior compartments of abdominal segments 5-7. Posterior-compartment
structures of A5-7 in the peripheral nervous system fuse in
mature embryos (Petschek and Mahowald). Hemizygotes for
lethal alleles, gt13z and gtX11, fail to hatch (Kaufman, 1973,
Genetics 74: s133); denticle belts of the fifth through the
seventh abdominal segments partially or completely absent;
internally corresponding neuromeres absent; eight abdominal
neuromeres disconnected from remainder. Head does not complete involution, shows characteristic "buttonhead" phenotype
with ventral skeleton extruded from the anterior end of the
larva (Mohler et al., 1989), pharynx and pharyngeal chitinized
sclerites shorter, and brain lobes somewhat smaller than normal; extensive cell death in epidermal and neural components
of embryo (Honisch and Campos-Ortega, 1982, DIS 58: 76-77).
Effect cell autonomous in mosaic embryos. (Gergen and
Wieschaus, 1986, Wilhelm Roux's Arch. Dev. Biol. 195: 49-62).
Germline clones viable (Garcia-Bellido and Robbins, 1983,
Genetics 103: 235-47). gt stocks (homo- or heteroallelic)
show an increase in the frequency of spontaneous mutations,
including deletions of y and w loci (Green, 1982, Proc. Nat.
Acad. Sci. USA 79: 5367-69); these stocks also synthesize DNA
of a reduced molecular weight and show many single-strand and
double-strand breaks, suggesting abnormalities in DNA metabolism (Narachi and Boyd, 1985). RK3.