Pregastrula and gastrula embryos exhibit nuclear defects, an excess of irregularly shaped internal chromatin masses, blastoderm nuclei are non-uniform in size and chromatin condensation and asynchronous in the cell cycle. Embryos have uneven blastoderm nuclear sizes, and fewer than normal nuclei at the beginning of gastrulation. There is an excess of irregularly shaped internal chromatin masses, and chromatin condensation is asynchronous. During preblastoderm and early blastoderm cleavages lagging chromosomes during anaphase are common.

Embryos derived from bcd⁶/bcd⁷ females show some development of at least thoracic and frequently head structures when injected at the anterior tip with cytoplasm taken from the anterior tip of wild-type embryos. Cytoplasm taken from the anterior tip of embryos derived from swa¹/swa² females shows reduced rescuing activity compared to wild-type cytoplasm when injected into the anterior tip of embryos derived from bcd⁶/bcd⁷ females. The phenotype of embryos derived from swa¹/swa² females is more or less unmodified if cytoplasm is removed from the anterior tip of the embryo.

maternal-effect lethal weak allele embryonic development normal but abnormal larval mouth parts prevent feeding. female-sterile.