Morphogen Gradients and Positional Information
A cell can work out where it is from the local concentration of a diffusible signal, and respond by switching on a different set of genes at different thresholds. This is how a smooth gradient produces sharp stripes, and why the same signal means different things in different tissues.
What a learner can do afterwards
- Explain how a graded signal is read as discrete cell fates through thresholds
- Predict the effect of doubling or removing a morphogen source on the resulting pattern
- Say why the same morphogen can specify different structures in two tissues
1 · Read
A morphogen drifts from its source, so each cell sits in a local concentration that says roughly how far from the source it is. Cells answer by expressing different gene sets above and below set thresholds. Since every cell in the embryo carries the same genes, fates differ only by which genes get switched on.
One threshold splits the field in two: above it fate A, below it fate B, with the boundary exactly where concentration crosses the line. Two thresholds carve three zones: high, middle, and low, each with its own fate. Smooth slope in, sharp stripes out.
Strengthen or double the source and every concentration rises, so boundaries slide outward and high-fate zones widen. Remove the source and the signal drains away, so the dependent fates never appear. The pattern tracks the dose.
The same morphogen can sculpt different structures in different tissues because each tissue offers a different set of ready genes. Location-specific signals start the cascade, but the cell's own program decides what the signal means.
Cells read a smooth signal against thresholds, so dose sets boundaries and tissue program sets meaning.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.