At 18
oC 76% of expected
scsisB-2 homozygotes survive to adulthood, but this drops to 35% when these animals are raised at 25
oC. 50-89% of
scsisB-1 homozygous adults lack upper humeral and anterior orbital bristles. With variable penetrance,
scsisB-1/
In(1)sc8Lsc4R adults lack ocellar, anterior orbital, posterior orbital, postvertical, upper humeral, anterior supraalar, notopleural, posterior postalar, lower humeral and presutral bristles. With variable penetrance
scsisB-1/
Df(1)sc19 adults lack all head bristles apart from the posterior vertical bristles, and all bristles of the dorsal thorax apart from the posterior notoplural, posterior dorsocentral and scutellar bristles.
Temperature-sensitive mutation.
Embryonic lethality of females rescued by maternal ectopic expression of
ac or
l(1)sc. Maternal
ac or
sc can rescue
scsisB-1 females.
Original hypomorphic allele recovered as a reversion of
sc3 to nearly wild-type
ac and
sc phenotype in hemizygote and homozygote. Locus also characterized by dominant effects of deficiencies and duplications of the ASC region and later by mutant alleles
sc10-1 and
acHw-49c that affect ASC functions more than
scsisB-1 functions.
scsisB-1 reduces viability of homozygous females and hemizygous females are lethal; yet hemizygous males fully viable. Dominant synergistic female-specific lethal interactions with loss-of-function alleles of
Sxl,
sisA, and/or maternal
da; magnitude of viability effects depends on genetic background and inversely correlates with background effects on male-lethal effects; interactions temperature-dependent, generally more extreme at higher temperatures. Female viability effects suppressed by gain-of-function
SxlM1 allele and by duplications of
Sxl+ or
sisA+. Duplication of
scsisB-1+ male-lethal in combination with duplication of
Sxl+ and/or
sisA+, more so at lower temperatures. Male lethality of duplication combinations suppressed by
Sxl-. Phenotype of 2X;3A intersexes strongly dependent on dose of
scsisB-1+. The dose-dependent interactions of this gene identify it as a positive regulator of
Sxl+ and part of the numerator of what is referred to as the X/A balance, the primary sex-determination signal. This is a character it shares with
sisA. RK2.
Temperature shift experiments showed that lowering sc activity in the presence of extra copies of
dpn+ results in the death of females but not males.
The viability of homozygous females ranges from 100% at 18oC to less than 1% at 29oC.
Flies show a mild bristle phenotype. Sex determination is affected much more strongly by
scsisB-1 than is neurogenesis, and the two aspects show different temperature dependencies. Temperature sensitive period for feamle lethal affect corresponds to peak of
sc expression between nuclear cycles 9 and 14 in the embryo.
Homozygous females show reduced viability hemizygous female lethal.
