Spatiotemporal gene expression - Wikipedia, the free encyclopedia: "Spatiotemporal gene expression refers to the activation of genes within specific tissues of an organism at specific times during development. Gene activation patterns vary widely in complexity. Some are straightforward and static, such as the pattern of tubulin, which is expressed in all cells at all times in life. Some, on the other hand, are extraordinarily intricate and difficult to predict and model, with expression fluctuating wildly from minute to minute or from cell to cell. Spatiotemporal variation plays a key role in generating the diversity of cell types found in developed organisms; since the identity of a cell is specified by the collection of genes activately expressed within that cell, if gene expression was uniform spatially and temporally, there could be at most one kind of cell."