McDougal Littell - Biology

Turning Genes Off

A typical organism, including ourselves, has in its genome the information necessary to produce several tens of thousands of proteins. Only a small fraction of those genes are turned "on" at any one time, however, as they are needed during different phases of development or as they are needed at different times in the life of an adult organism. How cells themselves turn genes "on" and "off" has been studied since Watson and Crick first described the double-helix in the middle of the 20th century, but more recently biologists have developed techniques to themselves to throw the switch on particular genes they are interested in studying. One way to do this is to create a genetically modified organism in which the gene of interest has been intentionally damaged or removed. These organisms are sometimes called "knock outs" because the action of a particular gene has been permanently disabled or "knocked out." A more recent and elegant technique for turning off the action of particular genes is RNA interference, or "RNAi," the discovery of which was awarded the 2006 Nobel Prize in Physiology or Medicine. RNAi uses a double-stranded RNA itself to degrade a particular RNA produced by a cell, which effectively silences the gene but temporarily and much more conveniently than creating a knock out organism. By turning particular genes off, biologists are now better positioned than ever before to understand how those genes are involved in development, in disease, or in normal cell function.