Most homozygotes die during the embryonic stage, although approximately 20% hatch and die as first instar larvae. Among those homozygous embryos that fail to hatch, 43% have a wild-type cuticle, 30% have a "double-line" cuticle phenotype (only two rows of denticles are present in each segment) and 22% have a "ghost" cuticle phenotype (the embryos have secreted cuticle, but no denticles are present).

5-HT2^C1644/Df(3R)HTRI embryos hatch, resulting in small larvae that die quickly with no obvious cuticle defects.

Homozygous embryos show altered cell movements during germband extension. Wild-type embryos show a slight ventral ectoderm contraction before the ectodermal extension starts, but this is not seen in homozygous embryos. During germband extension, ectodermal cells close to the pole cells in homozygous embryos have cell speeds four times that of equivalent cells in wild-type embryos, while the cell speed of these cells in heterozygous embryos is twice that of wild type.