Practice question

Segment polarity genes expressed in fourteen stripes maintain parasegment borders through local signaling. Core module includes wingless secreted from anterior row cells binding Frizzled and hedgehog secreted from posterior row binding Patched, establishing mutually reinforcing loop sustaining engrailed expression. Wingless is Wnt family member, hedgehog belongs to Hedgehog family, both lipid-modified morphogens. Notch governs neurogenesis, BMP patterns dorsal-ventral axis, FGF patterns trachea, not primary for segment polarity. Wnt-Hedgehog reciprocal signaling ensures compartment boundary stability, polarity preservation, and prevents fusion of adjacent parasegments during development and imaginal disc patterning later.