I noted previously that Scitable, a resource from Nature Education, was interesting but had some problems with the content [Scitable (and a weird piece on DNA barcoding)].
Well, more troubles.
Excerpt from Transposons, or Jumping Genes: Not Junk DNA?
Transposable elements (TEs), also known as “jumping genes” or transposons, are sequences of DNA that move (or jump) from one location in the genome to another. Maize geneticist Barbara McClintock discovered TEs in the 1940s, and for decades thereafter, most scientists dismissed transposons as useless or “junk” DNA. McClintock, however, was among the first researchers to suggest that these mysterious mobile elements of the genome might play some kind of regulatory role, determining which genes are turned on and when this activation takes place (McClintock, 1965).
At about the same time that McClintock performed her groundbreaking research, scientists Roy Britten and Eric Davidson further speculated that TEs not only play a role in regulating gene expression, but also in generating different cell types and different biological structures, based on where in the genome they insert themselves (Britten & Davidson, 1969). Britten and Davidson hypothesized that this might partially explain why a multicellular organism has many different types of cells, tissues, and organs, even though all of its cells share the same genome. Consider your own body as an example: You have dozens of different cell types, even though the majority of cells in your body have exactly the same DNA. If every single gene was expressed in every single one of your cells all the time, you would be one huge undifferentiated blob of matter!
The early speculations of both McClintock and Britten and Davidson were largely dismissed by the scientific community. Only recently have biologists begun to entertain the possibility that this so-called “junk” DNA might not be junk after all. In fact, scientists now believe that TEs make up more than 40% of the human genome (Smit, 1999). It is also widely believed that TEs might carry out some biological function, most likely a regulatory one—just as McClintock and Britten and Davidson speculated. Like all scientific hypotheses, however, data from multiple experiments were required to convince the scientific community of this possibility.