Drosophila 'Gap genes' are primary targets of maternal effect genes. What is the phenotypic result of a mutation in a gap gene?

Correct answer: Deletion of contiguous body segments

Gap genes such as Krüppel, Knirps, and giant define broad domains along the embryonic axis in response to maternal morphogen gradients. Loss-of-function mutations produce 'gaps' — the deletion of several consecutive body segments — leaving a discontinuous, truncated body plan.