Excerpt: Journals and conferences have been buzzing with new evidence that contradicts conventional notions that genes, those sections of DNA that encode proteins, are the sole mainspring of heredity and the complete blueprint for all life. Much as dark matter influences the fate of galaxies, dark parts of the genome exert control over the development and the distinctive traits of all organisms, from bacteria to humans. The genome is home to many more actors than just the protein-coding genes. The extent of this unseen genome is not yet clear, but at least two layers of information exist outside the traditionally recognized genes. One layer is woven throughout the vast “noncoding” sequences of DNA that interrupt and separate genes. Though long ago written off as irrelevant because they yield no proteins, many of these sections have been preserved mostly intact through millions of years of evolution. That suggests they do something indispensable. And indeed a large number are transcribed into varieties of RNA that perform a much wider range of functions than biologists had imagined possible. Some scientists now suspect that much of what makes one person, and one species, different from the next are variations in the gems hidden within our “junk” DNA.

Above and beyond the DNA sequence there is another, much more malleable, layer of information in the chromosomes. “Epigenetic” marks, embedded in a mélange of proteins and chemicals that surround, support and stick to DNA, operate through cryptic codes and mysterious machinery. Unlike genes, epigenetic marks are routinely laid down, erased and rewritten on the fly. So whereas mutations last a lifetime, epigenetic mistakes—implicated in a growing list of birth defects, cancers and other diseases—may be reversible with drugs. In fact, doctors are already testing such experimental treatments on leukemia patients. Researchers are also coming to realize that just about anything that can happen in the genome does happen, says Carmen Sapienza of Temple University, who started investigating epigenetic phenomena back when they were dismissed as minor anomalies. “There may even be fundamental mechanisms still to discover,” Sapienza considers. “I think we are entering the most interesting time yet in genetics.”

Scientific American