At 18oC 76% of expected scsisB-2 homozygotes survive to adulthood, but this drops to 35% when these animals are raised at 25oC. 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.
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.