With an ever-increasing number of genomes available for analysis, there has been a shift in emphasis away from the study of single genes and a greater attempt to understand gene expression at the network or systems level. A report in the March 1 PNAS shows that power laws—a universal mathematical dynamic—govern the process.

Hiroki Ueda and colleagues at the Center for Developmental Biology describe the mathematical principle underlying observed levels of gene expression. They used information from public databases of whole genome sequences and from their own microarray analyses. Proportional dynamics, also known as “rich-travel-more,” showed that power law levels of gene expression were observed not only in different organisms, but also within discrete organs or at specific developmental times in the same organism (PNAS, DOI:10.1073/pnas.0306244101, March 1, 2004).

The team examined how genes change their expression in different conditions and observed that highly expressed genes change more,...

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