bio

Positional information

Lewis Wolpert's 1969 idea that a cell knows what to become by sensing its position within a tissue, usually via the concentration of a morphogen. Wolpert illustrated it with a three-colored flag — the same strip of cells, but each cell picks its "color" from the concentration threshold it meets, so the whole strip partitions itself into three clean regions. A body is not drawn pixel by pixel; it is built from position-reading rules like this.