Practice question

Lewis Wolpert introduced French flag analogy illustrating how uniform field of competent cells could generate three distinct stripes if exposed to graded morphogen where high triggers blue genes, medium triggers white, low triggers red. Model predicted threshold-based activation of different transcriptional programs, later validated using synthetic promoters with varying affinity for Bicoid or Dorsal and quantitative imaging of gap genes. Gurdon's nuclear transfer tested genomic equivalence and totipotency, Meselson-Stahl tested semi-conservative DNA replication, Griffith tested bacterial transformation. Wolpert's model provided conceptual framework linking quantitative gradient to qualitative gene expression boundaries fundamental to modern pattern formation theory and positional information concept.