The phenotype of embryos resulting from crosses involving viable alleles of cos and Pka-R2^Cos-A1, Pka-C1^Cos-2 or Pka-C1^Cos-3 indicate a maternal effect on the interaction between cos and Pka-C1 and the interaction between cos and Pka-R2. If the female parent is heterozygous for a viable allele of cos and Pka-R2^Cos-A1, Pka-C1^Cos-2 or Pka-C1^Cos-3, and the male parent for Pka-R2^Cos-A1, Pka-C1^Cos-2 or Pka-C1^Cos-3, 11% of the embryos show a strong bicaudal phenotype (whereas the reciprocal cross produces less than 1% bicaudal embryos). cos^V2, Pka-C1^Cos-2/Df(2R)CA58 animals die at various stages of development. The most extreme imaginal phenotypes are observed in those flies that metamorphose but fail to hatch from the pupal case. Pattern duplications can occur on the anterior compartments of all segments of the body, by addition of extra pattern elements, with the possible exception of the clypeolabrum. In the abdomens the smaller anterior bristles are replaced by larger bristles, similar to those that are seen posteriorly, which point anteriorly. The dark pigment is also seen anteriorly. This deletion-duplication phenotype is reminiscent of that seen in cos mutant embryos.