Video narration
How can one signal steer nearby stem cells toward different fates? A smell is strongest near its source and fades as it spreads. In developing tissue, a morphogen is a signal whose concentration changes from place to place, creating a concentration gradient. Cells at different positions receive different amounts. A cell receiving one amount can activate one set of genes; farther away, a different amount can activate a different set. Those changes help pattern tissue and guide what cells become. The same signal does not give every cell the same instruction. Cells respond to the amount they receive, in their particular context. A high level does not automatically mean the same body part in every tissue. Timing, a cell's state, and other signals shape its fate. So one signal guides different outcomes, but it is not a complete blueprint.