“Most species maintain abundant genetic variation and experience a wide range of environmental conditions, yet phenotypicâ€”or physicalâ€” differences between individuals are usually small,” Siegal explained. “This phenomenon, known as phenotypic robustness, presents an apparent contradiction: if biological systems are so resistant to variation, how do they diverge and adapt through evolutionary time?”
Siegal and Levy sought to identify genes that contribute to phenotypic robustness in yeast by analyzing the differences in their phenotypes in a comprehensive collection of single-gene knockout strainsâ€”that is, they removed these genes to determine if the resulting phenotypes were more variable from cell to cell.
They determined that approximately 5 percent of yeast genes, or approximately 300 genes, break phenotypic robustness when knocked out. These genes tend to interact genetically with a large number of other genes, and their products tend to interact physically with a large number of other gene products. When they are absent, the
cellular networks built from their interactions are disrupted and physical differences in the species result. In nature, the researchers hypothesized, some individuals might then have physical features that yield an advantage over the others.
A certain amount of change is necessary, but too much, and the species devolves into chaos. Even more, allowing change doesn’t guarantee that change works; it is then tested and if destroyed, not taken back up into the genomic library.
Lessons we can all use.