Practice question

Drosophila early embryogenesis is dominated by syncytial specification, where rapid nuclear divisions occur without cytokinesis, generating a syncytial blastoderm with nuclei sharing common cytoplasm. Maternal gradients including Bicoid, Hunchback and Caudal diffuse among nuclei, establishing positional codes before membranes enclose cells. Gap, pair-rule and segment polarity genes activate sequentially based on threshold responses to these gradients through cooperative enhancer binding. This mode permits long-range morphogen action unrestricted by membranes, distinct from autonomous or conditional mechanisms requiring localized determinants or cell-cell signaling after cellularization and essential for fast insect development.