On this date, the Nobel Assembly at the Karolinska Institute awarded the Nobel Prize in Physiology or Medicine jointly to Richard J. Roberts and Phillip A. Sharp, who in 1977 independently discovered that individual genes could be discontinuous, that is, a given gene could exist in the genetic material not as one continuous segment of DNA but as several, well-separated segments. A gene may thus consist of several segments, usually termed exons, separated by intervening, irrelevant stretches of DNA called introns. Such “split genes” are typically found in eukaryotes but not in prokaryotes, which have very compact genomes.
The discovery of split genes has radically changed our view on how the genetic material has changed during the course of evolution. Previously, it was thought that only minor alterations (mutations) occur within genes, producing gradual change in the genetic material. However, now it seems likely that higher organisms, in addition to undergoing mutations, may utilize another method that changes the genetic material: rearrangement or shuffling of exons that produces proteins with new functions. This can take place through crossing-over during gamete formation. This hypothesis was bolstered by the later finding that individual exons in several cases correspond to building modules (domains) in proteins and each domain has a specific function. An exon in the gene would thus correspond to a particular subfunction in the protein, and the shuffling of exons could result in a new combination of subfunctions in a protein. This kind of genetic recombination could accelerate evolution significantly.