Transposons, the movable genes
Posted: Tuesday, December 31, 1996
Transposons, the movable genes that have long been derided as "selfish" bits of DNA, may be a missing link in evolution, according to John McDonald of the University of Georgia. Until just 50 years ago, scientists thought of the genetic code as a fixed sequence of instructions. But pioneer geneticist Barbara McClincock showed that, in fact, some genes jump around. These genes, which scientists now call transposable elements, or transposons, have been found in every organism studied. The function of transposons is not well understood; many researchers regard them as junk in the genome.
In the March, 1998 issue of Trends in Ecology and Evolution, McDonald argues that transposons played an essential role in life's evolution. Higher organisms possess two chemical mechanisms designed to silence certain parts of the genome that should not be active. McDonald believes that chemical processes arose as a way to suppress harmful mutations that could be caused by jumping transposons, but their influence has gone much farther. The gene-silencing mechanisms may have served a crucial role in regulating the genome at two key moments in evolutionary history, smoothing the transitions from single-cell to multi-cell organisms and from invertebrates to vertebrates.
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