Processes such as the development from a caterpillar into a butterfly entail dramatic changes in patterns of gene expression. The expression levels of thousands of genes can be monitored through the use of DNA arrays. At the right, a DNA microarray reveals the expression levels of more than 12,000 human genes; the brightness and color of each spot indicates a change in the expression level of the corresponding gene.
[(Left) Cathy Keifer/istockphoto.com. (Right) Agilent Technologies.]