An organism’s DNA contains its genes and all the necessary information to control when, where, and how specific traits develop. In this way, DNA is like a blueprint describing how to construct different parts of a body. Genes are part of this blueprint — they are the pieces of an organism’s DNA that encode the directions for making proteins. Organisms need proteins because the cells use these as raw materials to make the structures outlined in the DNA blueprint.
However, some genes (sometimes called “control genes” or “regulatory genes”) encode proteins that regulate other genes. These proteins may directly interact with other pieces of DNA, they might trigger events that turn other genes on or off, or they may bind to other proteins that affect these processes. These special proteins are like bosses who determine which additional proteins (acting as workers) will be needed to get the job done in the cell. Some are powerful enough to send out orders, like “Build an eye here!” or “Put a leg over there!”
Looking deeper into eye development in mice, scientists discovered a gene called Pax6 that seemed to be involved in making mouse eyes. First, biologists discovered that wherever Pax6 is turned on (or “expressed”), the mouse embryo will eventually develop an eye. Second, scientists discovered that when Pax6‘s DNA sequence is disrupted by a mutation, the mouse carrying that mutation develops with very small eyes or with no eyes at all — prompting scientists to nickname the gene Small Eye. These two lines of evidence strongly suggest that Pax6 helps build eyes as the mouse develops. In fact, Pax6 seems to be one of those bossy regulating genes that helps to direct the development of eyes in mice. When Pax6 is turned on, it starts sending out directions to other genes to get to work building an eye!