Since Watson and Crick discovered DNA's structure in 1953, scientists have realized the double helix is only one part of our genetic makeup. The latest portrait of our basing building blocks.
By Mary Carmichael NEWSWEEK
Dec 10, 2007 Issue
The difference, it turned out, wasn't due to the mice's genetic code, nor was it due to the environment. It lay instead in a mechanism that was mediating between the two. A gene in the sickly yellow babies was making a disease-causing protein called Agouti, which also affects coat color. The brown babies had the same gene, but it wasn't making much of anything. It had mostly stopped working. The brown babies' mothers had eaten a special diet during pregnancy: one rich in folic acid, which floods the body with tiny four-atom configurations called methyl groups. These methyl groups had infiltrated the growing brown mouse embryos and latched onto the flawed gene, shutting it down. This was the solution to the mystery: Jirtle had vividly illustrated why, at the biochemical level, the genetic sequence alone doesn't always equal destiny. Four humble atoms had been enough to override a serious defect in the brown babies' genomes. And what was true of the mice turned out to be true of men: there is much more to our nature than the plans laid in the genetic code.