Feb. 18, 2010 For years, biologists have wondered how it is
possible that not every person who carries a mutated gene
expresses the trait or condition associated with the mutation.
This common but poorly understood phenomenon, known as
incomplete penetrance, exists in a wide range of organisms,
including humans. Many mutations in genes that are linked to
diseases, including Parkinson's disease and Type 1 diabetes, are
incompletely penetrant. Some of this variation may be due to
environmental factors and the influence of other genes, but not
all: It has been shown that genetically identical organisms
living in the same environment can show variability in some
incompletely penetrant traits. Now, a team of MIT biophysicists
has demonstrated that some cases of incomplete penetrance are
controlled by random fluctuations in gene expression. "It's not
just nature or nurture," says Alexander van Oudenaarden, leader
of the research team and a professor of physics and biology at
MIT. "There is a random component to thi