Practice question

Morphogens encode positional information through concentration variation across tissue, converting analog gradient into digital transcriptional domains. Secreted source creates descending gradient; cells read local dose via receptor occupancy and intracellular effector activity such as Gli ratio for Shh or Smad phosphorylation for BMP. Distinct enhancer affinities cause different targets to activate only above specific thresholds, generating striped fate domains. This mechanism underlies Drosophila Decapentaplegic gradient, vertebrate limb Shh gradient and retinoid gradient, and is fundamental to embryonic axis patterning and French flag interpretation.