Nessa Carey writes: When President Obama delivered a speech at MIT in 2009, he used a common science metaphor: “We have always been about innovation,” he said. “We have always been about discovery. That’s in our DNA.” Deoxyribonucleic acid, the chemical into which our genes are encoded, has become the metaphor of choice for a whole constellation of ideas about essence and identity. A certain mystique surrounds it. As Evelyn Fox Keller argues in her book The Century of the Gene, the genome is, in the popular imagination at least, the secret of life, the holy grail. It is a master builder, the ultimate computer program, and a modern-day echo of the soul, all wrapped up in one. This fantasy does not sit easily, however, with geneticists who have grown more aware over the last several decades that the relationship between genes and biological traits is much less than certain.
The popular understanding of DNA as a blueprint for organisms, with a one-to-one correspondence between genes and traits (called phenotypes), is the legacy of the early history of genetics. The term “gene” was coined in 1909 to refer to abstract units of inheritance, predating the discovery of DNA by forty years. Biologists came to think of genes like beads on a string that lined up neatly into chromosomes, with each gene determining a single phenotype. But, while some genes do correspond to traits in a straightforward way, as in eye color or blood group, most phenotypes are far more complex, set in motion by many different genes as well as by the environment in which the organism lives.
It turns out that the genetic code is less like a blueprint and more like a movie script, subject to revision and reinterpretation by a director. This process is called epigenetic modification (“epi” meaning “above” or “in addition to”). Just as a script can be altered with crossed-out words, sentences or scenes, epigenetic editing allows entire sections of DNA to be activated or de-activated. Genes can be as finely tuned as actors responding to stage directions to shout, whisper, or cackle. [Continue reading…]