redOrbit Staff & Wire Reports – Your Universe Online
Despite the complex structure of the human genome, more than 90 percent of it has no important biological function, scientists from Oxford University report in research published in the July 24 edition of the journal PLOS Genetics.
In fact, according to the study authors, just 8.2 percent of the genome is actively operating to make us who we are and keep our cellular systems functioning. The rest, Telegraph science correspondent Sarah Knapton wrote on Friday, is a mixture of leftover material from our evolutionary past, or has no function whatsoever.
The new percentage is a far cry from previous claims, made by ENCODE (Encyclopedia of DNA Elements) project scientists in 2012, that 80 percent of the human genome possessed some type of biochemical function. The Oxford researchers noted that those controversial claims left many experts disputing the ENCODE’s team’s broad definition of function, and that it should be demonstrated that activity occurring on DNA has a reason for taking place.
In reaching the 8.2 percent figure, the authors of the PLOS Genetics study said they worked to identify how much of the genome has avoided changing or evolving over the past 100 million years, as this serves to indicate these pieces of genetic code possess some important function which needs to be preserved and maintained.
“This is in large part a matter of different definitions of what is ‘functional’ DNA,” joint senior author Professor Chris Pointing of Oxford’s MRC Functional Genomics Unit said in a statement. “We don’t think our figure is actually too different from what you would get looking at ENCODE’s bank of data using the same definition for functional DNA.”
“But this isn’t just an academic argument about the nebulous word ‘function’. These definitions matter,” he added. “When sequencing the genomes of patients, if our DNA was largely functional, we’d need to pay attention to every mutation. In contrast, with only 8 percent being functional, we have to work out the 8 percent of the mutations detected that might be important. From a medical point of view, this is essential to interpreting the role of human genetic variation in disease.”
Of the functional 8.2 percent, slightly more than one percent of human DNA accounts for the proteins required to carry out nearly all of the body’s essential biological processes, Knapton said. The other seven percent is believed to play a role in activating or deactivating genes that encode proteins in response to various factors, at different times and in different regions of the body. These are known as the control and regulation elements.
Researchers Chris Rands, Stephen Meader, Chris Ponting and Gerton Lunter used a computational approach to compare the complete DNA sequences of humans with those of other mammals, including mice, rabbits, dogs and horses. Their plan was to find where chunks of DNA were inserted into or deleted from the mammals’ genome, which occurred randomly except when natural selection acted in order to preserve DNA considered to be functional.
“We found that 8.2 percent of our human genome is functional,” concluded Dr. Gerton Lunter from the Wellcome Trust Centre for Human Genetics at Oxford. “We cannot tell where every bit of the 8.2 percent of functional DNA is in our genomes, but our approach is largely free from assumptions or hypotheses. For example, it is not dependent on what we know about the genome or what particular experiments are used to identify biological function.”
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