The random fluctuations—also known as noise—of gene expression could account for phenotypic variations ranging from the minor—such as different fingerprints in identical twins—to the major, including normal embryonic development, according to a study in the May 27 Science.

The authors, Erin K. O'Shea and Jonathan M. Raser at the Howard Hughes Medical Institute, University of California at San Francisco, say their measurements of noise in single budding yeast cells suggest that noise also provides a means, albeit temporary, of cellular adaptation to the environment.

O'Shea and Raser cloned two—cyan and yellow—fluorescent protein reporter genes under the control of identical budding yeast PHO5 gene promoters to look at cell-to-cell differences in a population of yeast cells. When all cells express similar quantities of the fluorescent proteins at similar times, then little variability—meaning little randomness—in gene expression is occurring, Raser said.

"If we see substantial differences between two independent but identical genes—if...

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