Practice question

Kruppel transcription factor gap gene shows bell-shaped expression centrally. Activation requires intermediate Bicoid and Hunchback co-activation; repression by high Hunchback anteriorly, Knirps and Giant posteriorly defines borders. Bicoid alone insufficient, high Hunchback represses. Combinatorial integration illustrates threshold model for morphogen interpretation. Wingless does not regulate Kruppel; instead regulates engrailed later. Dual activation ensures robust positioning of Kruppel stripe which then represses abdominal gap genes, forming mutually repressive network sharpening gap domains critical for positioning thorax and establishing correct thoracic identities during early embryonic patterning and cellular blastoderm stage formation.