From “Parasites or Not? Transposable Elements in DNA of Fruit Flies May Be Beneficial” (ScienceDaily Feb. 3, 2012), we learn,
Nearly all organisms contain pieces of DNA that do not really belong to them. These “transposable elements,” so called because they are capable of moving around within and between genomes, generally represent a drain on the host’s resources and in certain cases may lead directly to disease, e.g. when they insert themselves within an essential host gene. The factors that govern the spread of transposable elements within a population are broadly understood but many of the finer points remain unclear. New work at the University of Veterinary Medicine, Vienna (Vetmeduni Vienna) may pave the way to a more profound knowledge of the intracellular battle that is constantly being played out between the host and invading DNA.
But the battle is very complex, and one possibility that the Vetmeduni research raised is that some transposable elements are not parasites or menaces but benefactors:
the scientists found about a dozen sites of insertion that were more frequent in the population than would be expected from their age (assessed via a different method). It seems, then, that there is positive selection for transposable elements at these sites, suggesting that insertion has a beneficial effect on the host. Such an effect had previously been shown for two insertions that give increased resistance against insecticides and these cases were refound by Schlötterer’s analysis.
The functions of the genes closest to the remaining insertions are highly diverse, so how the transposable elements may benefit the flies is unclear. As Schlötterer puts it, “perhaps we shouldn’t really think of transposable elements as parasites at all. They represent a way for organisms to increase their genetic repertoire, which may be advantageous in helping them meet future challenges.”
More work is surely needed, but betting against function is looking more like a bad idea all the time.
See also: Carefully preserved jumping gene in corn shows how intelligent design produces massive changes