'Correspondence re “Selfish DNA”'

Date:
1980
Reference:
PP/CRI/H/6/13/7
Catalogue details

Licence: In copyright

Credit: 'Correspondence re “Selfish DNA”'. Source: Wellcome Collection.

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    rSeifish' DNA 9 s only purpose By Kevin McKean AP Science Writer NEW YORK — One of the great mysteries of modern biology is why so much of the DNA, or genetic material, : higher animals has no apparent I piu-pose. Now scientists say this may I be selfish DNA whose only function is to perpetuate itself. The proposal, stated in two articles in the latest issue of the British scien tific magazine Nature, was offered by four scientists, including Nobel prize winner Francis H.C. Crick, co-dis coverer of the structure of DNA. In the articles, the scientists at- I tempt to explain the puzzling fact that I higher animals, including humans, I seem to have much more DNA than they need. DNA, or deoxyribonucleic acid, is the helical molecule in the nuclei of cells that carries the genetic blueprint for making a new creature. In bacte ria, about 99 percent of the DNA is known to code the proteins used to build cells. But in more complex animals, less and less of the DNA appears to be directly involved in creating new creatures. In mammals like human beings, more than 90 percent of the DNA seems simply superfluous. This excess DNA has become particularly troublesome to scientists in the last five years, as new tech niques have made it easier to read the code of DNA and see how much of it is simply nonsense. Scientists have advanced two main explanations. Some have said the ex cess DNA has a regulatory purpose that just isn't understood yet. Others have proposed that the extra DNA may make it easier for genes to mu tate and recombine, giving creatures with excess DNA the ability to evolve faster than simpler forms of life. But Crick and Leslie Orgel of the Salk Institute in La Jolla, Calif., and W. Ford Doolittle and Carmen Sapien za of Dalhousie University in Halifax, Nova Scotia, Canada, say there may be another explanation. Doolittle ex plained in a telephone interview Wednesday : All you need for natural selection to operate is something with the ability to replicate itself and to mutate. This is the case with DNA. It's almost logically inevitable that some DNA whose only purpose is to replicate itself will arise. ' ' One example of such selfish DNA may be the so-called transposons, he said. These are DNA sequences having no known purpose that are re peated over and over in the genes of animals. Transposons seem to have evolved with the ability to copy themselves and insert the copies into new places on the DNA molecule, Doolittle said. In some cases, this helps the animal survive, as when a bacterial transpo- son carries a gene that is resistant to an antibiotic. But many < have no such helpful genes, Doolittle said, and their only purpose appears to be their own survival. The spread of selfish DNA se quences within the (genetic material) can be compared to the spread of a not-too-harmful parasite within its host, Orgel and Crick said. The only known disadvantage of selfish DNA is the energy wasted in duplicating it each time a cell divides. But in higher animals, this may be only a small disadvantage. I wouldn't say it was unreasonable to say that 90 percent of the DNA you carry around is simply playing games of its own, said Doolittle. It's sort of humbling — to look at yourself as just a bag for replicating DNA. ' '