Switch genes are not coding genes, but are pseudogene DNA that have the ability to switch on and off genes that do replicate into protein. The occurrence when switch genes turn off coding genes is called “gene silencing” [http://en.wikipedia.org/wiki/Gene_silencing].
One of the best and fascinating explanations you will ever find on how switch genes work is presented between the 45:00 minute and 55:00 minute segment in the PBS NOVA video, “What Darwin Never Knew” [http://www.pbs.org/wgbh/nova/evolution/darwin-never-knew.html]. In this video clip, researchers were studying how the fir of field mice match in color the surrounding terrain to camouflage itself from being readily seen by predators.
Scientists examined dark spots on a wing of a fruit fly. Some species of fruit flies have these spots, others don’t. Molecular biologists sifted through the DNA of these fruit fly and found the code that produced the spots, calling it the “paintbrush” gene. All species of fruit fly had the paintbrush gene, but only one type of fly actually had the spots appearing its phenotype.
At the 50:35 minute mark of the video, the answer was found, which is a switch gene. What happens next is amazing. The researchers then took a gene that glows in the dark found in jellyfish, and injected into the genome of the fruit fly. The experiment worked in that the wing spots in fruit flies illuminated (51:30 minute mark). The explanation of switch genes then begins at the 52:00 mark in the video.
Scientists have found many applications of how switch genes work, [http://www.sciencedaily.com/releases/2008/01/080124135504.htm]. In fact, it’s hopeful that understanding switch genes will allow us to find a cure for cancer, [http://www.sciencedaily.com/releases/2010/09/100924134953.htm].
A recent article in National Geographic discussed how biologists were puzzled that frogs were suddenly evolving teeth, [http://news.nationalgeographic.com/news/2011/02/110209-frogs-teeth-evolution-science/?source=link_fb20110212frogsevolveteeth]. Switch genes are a simple explanation for why frogs would evolve teeth. The hypothesis is simply the teeth gene is present in all frogs just like the wing spot gene is present in all drosophila (fruit flies). A simple switch gene in this instance switch on the frog’s ability to grow teeth.