The Genome in Turmoil

[n2doc]

BY NESSA CAREY

hen 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.

...

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.

These directions are encoded through what are essentially little deposits of specific chemicals onto our DNA and proteins called histones, around which our DNA is wrapped like Christmas lights around a tube. The most common form of epigenetic editing is called methylation, in which a methyl group (one carbon and three hydrogen atoms) latches on to either the DNA or the histone. DNA methylation switches off gene expression, while histone methylation may increase or decrease gene expression, depending on the type of methylation and where on a histone it’s deposited.

These modifications don’t change the underlying genetic code, but influence how genes are expressed. Some modifications can last a lifetime, keeping certain genes switched off forever, like whited out lines running through entire scenes of our genetic script. If you don’t have a tooth growing in your eye or a liver in your knee, thank your epigenome: the differences controlling cell lineage are dictated predominantly by DNA methylation. Other modifications are more like the Post-it notes, influencing incremental degrees of gene expression depending on environmental circumstances—allowing cells to react quickly to changes. Permanent changes often involve large amounts of methylation, which make the DNA cling so tightly to the histone that it can’t be read, rather like glued-together pages of a movie script.

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http://nautil.us/issue/2/uncertainty/the-genome-in-turmoil

[pscot]

1. Does this open the door to Lysenkoism?

That would be an embarrassment.

[Socialistlemur]

2. Nah

The epigenetic imprint isn't passed on. What does go on is the tendency to be imprinted. But if the imprinting event doesn't take place, then an individual carries on without the given modification. This means, for example, that if you have a tendency to suffer from POst traumatic stress syndrome, this is genetic, but you also have to be stressed to get it. If you suffer from it but don't let your children get sent to a war like Iraq or Vietnam, and get out of the ghetto so you don't have to fear bullets flying, you may be fine.