survey the expression of all human genes simultaneously and map the specific subset of genes that are active in a given cell at a given point in time. One surprising finding from the field of “functional genomics” is that the expression of a specific gene is often more an exception than the rule. Cells are highly selective about which genes they express, and our DNA encodes a great deal more genetic potential than is realized in RNA and protein. Even more striking has been the discovery that the social world outside our bodies influences which genes are transcribed within the nuclei of our cells (the RNA “transcriptome”).
