Correct option is D
Correct Answer: Option 4
Explanation: -Axis specification in Drosophila follows a hierarchical gene-regulation sequence: gap genes → pair-rule genes → segment-polarity genes. -Krüppel is a gap gene involved early in broad regional patterning. -Hairy and fushi tarazu are pair-rule genes that refine segmental boundaries. -Wingless is a segment-polarity gene essential for final stabilization of segments. -Hence, the correct sequential order is Krüppel → hairy → fushi tarazu → wingless.
