Initial pattern is sparse. To visualize the pattern of differentiation prior to the appearance of visible heterocysts, the gene encoding green fluorescent protein (from a jellyfish) was fused to the differentiation-specific gene, hetR. This procedure allows hetR expression to be seen as green fluorescence. Hours after inducing differentiation, hetR is expressed in groups of adjacent cells that otherwise appear no different from vegetative cells. Several hours later, heterocysts have appeared, and hetR expression is confined to those cells.