Practice question

British developmental biologist Lewis Wolpert proposed French flag model to explain how single morphogen gradient can generate multiple discrete territories in a field of cells. High concentration near source activates blue genes, intermediate concentration activates white genes, low or absent activates red, analogous to French tricolor flag. Cellular interpretation depends on threshold responses mediated by differential enhancer affinity and cooperative transcription factor binding. Classic illustrations include Bicoid activating distinct gap genes along anteroposterior axis and Activin concentration patterning Xenopus mesoderm into dorsal notochord versus ventral blood and intermediate muscle, underpinning positional information concept.