You get your genes from your parents — that principle is the foundation of current evolutionary theory. But what if genes could jump from organism to organism in passing, like a contagious disease? More and more evidence suggests that this sort of thing happens regularly. Most recently, a team of Berkeley scientists has shown that totally different species of plants have exchanged DNA.
When genes jump out of one organism’s genome into another’s, it’s called horizontal transfer — as opposed to vertical gene transfer from parent to child. Mostly this happens among bacteria, but the Berkeley team, led by microbiologist Damon Lisch, has shown that genes moved between millet and rice plants — millions of years after the families of those two species could no longer breed. It’s the first well-documented case of this sort of interspecies hanky-panky: specifically, the movement of outside DNA into the nucleus of a plant’s reproductive cells. How do the genes move? That question makes Lisch’s eyes light up. “We’re talking about a section of DNA here, but it acts more like a parasite,” he says. “It would seem like science fiction if it [weren’t] reality.”
Scientists have been tracking these jumping genes — or transposable elements — since the 1950s. They already knew transposons moved around on a single genome, creating variations such as striped kernels in corn. These jumping genes also have been tracked in bacteria. But scientists didn’t realize these genes could leap from one species to another until now.
Transposons make copies of themselves from one section of the double helix to another, sometimes wreaking havoc on gene function. In other cases, they have conferred useful abilities—such as antibiotic resistance — to their hosts. The implications for evolutionary theory are immense. Instead of each species having to develop adaptations on its own and pass them on through offspring, they can pick up genes—and the traits that go with them—from the organisms around them. That’s how bacteria often develop resistance to multiple antibiotics: They swap their defensive tricks. These findings could revolutionize our understanding of human evolution as well: The mapping of the human genome shows that about half of our genetic code is derived from transposable elements.
From the November December 2006 Life After Bush issue of California.
