1. Introduction to Mobile DNA

Charles Darwin would be surprised. Indeed, even present day scientists are surprised by the existence of mobile DNA. Consider the skepticism within the scientific community that greeted Barbara McClintock, already a highly-respected scientist, when she announced that she had found what appeared to be mobile DNA in maize plants (McClintock, 1950). DNA was the genetic material, so it must be static, stable, and immobile. The mutation rate had been determined to be ~10^-8 per nucleotide, or building block, of DNA per generation—very low indeed. How and why would some DNA move from place to place in a genome? Scientists are still grappling with these questions. Two hundred years removed from Darwin’s birth, and we’re still wondering how mobile DNA with all its detrimental effects on organisms could have reached such high proportions in the genomes of mammals and plants. Yet mobile DNA is found in all forms of living things, including plants, animals, bacteria, and archea. The genome seems to cherish its ability to make rapid changes by rearranging some of its parts as opposed to the slow change afforded by the nucleotide mutation rate.