““In the late 1970s, scientists working on gene-silencing discovered that the attachment of a small molecule-a methyl group-to DNA was correlated with a gene's turning off. These methyl tags decorated the strands of DNA, like charms on a necklace, and they were recognized as shutdown signals. The production of RNA ceased and the expression of the gene was silenced. If a chromosome was heavily decorated by methyl tags, then perhaps the whole chromosome could be silenced.””
