Homozygous bic females produce variable numbers of eggs that fail to hatch (e.g., 25-50%). bic/Df(2R)vgB females produce higher embryonic mortality. Males of either genotype are normal. A wide array of developmental anomolies observed among arrested embryos. Many fail to show outward signs of initiation of development, although in at least some zygotes nuclear divisions can be demonstrated. Others show replacement of anterior embryonic segments by a mirror-image set of posterior segments. The majority of these bicaudal embryos are symmetrical with opposing sets of the two to five posterior-most segments; mirror-imaged structures include denticle belts, posterior spiracles, Malpighian tubules, genital disc, and posterior midgut invagination. Polar cells form at the original but not the duplicated posterior end. Asymmetrical bicaudal embryos such as 3/6 or 3/7 have fewer duplicated than original posterior segments. Other embryos have the head replaced by posterior abdominal structures or show abnormal development of the cephalopharyngeal apparatus. Finally, some embryos are foreshortened and seem to lack internal segments. Maximum production of bicaudal embryos occurs in the first eggs produced by females developing at 28-29. The incidence of bicaudal embryos falls rapidly during the first 60 hr after eclosion. Incidence of bicaudal embryos and nondeveloping eggs depends on genotype: bic/Df(2R)vgB > bic/Df(2R)vgD > Df(2R)vgB/+ > bic/bic > bic/+ = 0.

An incompletely penetrant dominant female-sterile mutation; heterozygous females produce 60% apparently unfertilized eggs. In heterozygotes with Bic-C or Bic-D, E(Bic) causes a substantial increase in the incidence of double-abdomen embryos, but E(Bic)/+ females produce normal embryos.