Reprinted with permission from AAAS
 COLORFUL NOISE: Bacterial cells simultaneously expressing two different fluorescent proteins (red and green) from identical promoters. Because of stochasticity or noise in the process of gene expression, even two nearly identical genes often produce unequal amounts of protein.

Listen. Gene expression tends to be noisy. As beautifully regulated as it sometimes seems, the path from gene to message to protein picks up interference; a nagging variability in expression rates that can be found between seemingly identical organisms and even between identical genes in the same cell. For researchers, this noise, commonly known as stochasticity, renders results difficult to interpret.

Reports dot the literature about unexplained randomness, such as variable chemotactic responses observed in clonal bacteria grown under homogenous conditions. Eukaryotes, too, share this randomness: Protein levels in an egg cell account for variable phenotypes in genetically identical lab mice; that variability from a single cell...

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