What looks like a simple light board, is actually a DNA microarray, and what you see here is a visual representation of genes responding to a chemical. Scientists know how a chemical affects gene activity in a cell by comparing the genes in exposed cells to those in unexposed cells. Each dot represents one gene. Red dots indicate genes that were more active in the exposed cells, green dots indicate genes that were less active, and yellow dots indicate genes that were equally active in both exposed and unexposed cells.courtesy of Jeff Tucker, NIEHS/NIH/DHHS