Or is it epigenetics?:
The genetic code in mammals may have gained another letter—or at least a significant footnote. Textbooks speak of four DNA building blocks, whose order specifies genes. But researchers in the field of epigenetics have also identified four chemically modified versions of these nucleoside bases, which affect how genes are expressed. Three of them are altered versions of cytosine, one of the original four bases. The last, methylated adenine, is mired in controversy about whether it exists in mammals.
Now, researchers at Yale University have not only identified plenty of this modified base in mouse embryonic cells, but also found it plays a key role in the development of the placenta. The methylated base—methyladenine for short—gives cells another epigenetic tool for turning genes on or off during normal development or in disease. “This is a very important study for our understanding of the role of [methylated adenine] in gene regulation,” says Peng Jin, a geneticist at Emory University who was not part of the work…
But even if the discovery is confirmed, Peng says he is leery of calling the modified adenine an addition to the genetic code. “Maybe [part] of the ‘epigenetic code’ instead?”
Elizabeth Pennisi, “Controversial DNA modification could play key role in placenta development” at Science
Wow. An epigenetic code.
See also: Epigenetic change: Lamarck, wake up, you’re wanted in the conference room!
Hat tip: Heather Zeiger