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#experimental model

2 public questions tagged with this topic.

Morphogen Induction-l

Which experimental model demonstrated that different morphogen concentrations activate different genes?

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.

Ref: Wolpert, Principles of Development, 6th ed., Chapter 5: French Flag Model and Threshold Genes.

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Morphogen Induction-l

Which of the following is an example of a morphogenetic gradient experiment?

Morphogenetic gradient experiments test dose-dependent fate induction rather than simple presence or absence of signal. In Xenopus, isolated animal cap ectoderm cultured with titrated recombinant Activin differentiates into ventral mesoderm at low dose, muscle at intermediate dose and organizer plus endoderm at high dose, recapitulating in vivo mesoderm patterning along vegetal-animal axis. This demonstrates diffusible factor encoding multiple fates by threshold via Smad2. Spemann organizer transplantation tests inductive capacity not quantitative gradient, CRISPR knockout removes gene but not gradient quantification, GFP tagging visualizes spindle not patterning. Activin dose-response remains classic quantitative proof for morphogen concept in vertebrates.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Activin Gradient Experiments and Morphogen Proof.

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