LONDON, July 25 (Xinhua) -- Only 8.2 percent of human DNA is likely to be doing something important or "functional," in a departure from previous figures, according to a British study published in American scientific journal Plos Genetics Friday.
In 2012, scientists involved in the Encyclopedia of DNA Elements (Encode) project stated that 80 percent of human genome had some biochemical functions.
However, that claim has been controversial, with many arguing that the biochemical definition of "function" was too broad and that just because an activity on DNA occurs, it does not necessarily have a consequence.
To reach their latest figures, researchers from Oxford University took advantage of the ability of evolution to discern which activities matter and which do not.
They identified how much human genome avoided accumulating changes over 100 million years of mammalian evolution -- a clear indication that the DNA mattered and that it had some important function that needed to be retained.
According to their findings, the rest of human genome is leftover evolutionary material, parts of the genome that have undergone losses or gains in the DNA code -- often called "junk DNA."
Researchers also explained that, not all of the 8.2 percent is equally important. A little over 1 percent of human DNA accounts for the proteins that carry out almost all of the critical biological processes in the body.
The other 7 percent is thought to be involved in the switching on and off of genes that encode proteins. This takes place at different times, in response to various factors, and in different parts of the body.
"This is in large part a matter of different definitions of what is 'functional DNA,'" joint senior author Chris Pointing of Oxford University said.
"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," he added. Editor: Fu Peng