As the complete human genome sequence emerges, research shifts from questions of genomics to those of proteomics--determining the function of individual gene products and mapping global gene expression patterns. Gene expression patterns change continually during the course of tissue development and differentiation. The expression of different gene products at any given time within a particular cell defines the cell's characteristics and helps determine how it will react to external stimuli. Alterations in these expression patterns often accompany various disease states. Thus, understanding how the expression of certain genes is toggled on and off during normal development and in disease, and how environmental factors affect these patterns, helps researchers focus drug development efforts.

Researchers have many tools at their disposal to measure differential gene expression.1 Certainly microarrays are a viable option,2 but relatively few researchers have access to this big ticket technology. Instead scientists often rely on relatively "low...

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