Only about 8.2 percent of human DNA is believed to have an important role.
Past studies have suggested 80 percent of human DNA has a biochemical function, but this new research disputes that idea, University of Oxford reported. The study, published recently in Plos Genetics, suggests past definitions of "functional" have been too broad.
"This isn't just an academic argument about the nebulous word 'function'. These definitions matter. 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 [eight percent] being functional, we have to work out the [eight 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," said joint senior author Professor Chris Ponting of the MRC Functional Genomics Unit at Oxford University.
To make their findings the researchers looked at how much of the human genome has avoided accumulating changes over the past 100 million years; this indicates the DNA has an important function that must be preserved. The rest of the DNA that has undergone numerous losses or gains is considered to be leftover evolutionary material, or "junk DNA. The team took a computational approach to comparing completed DNA sequences in humans as well as other mammals such as guinea pigs and horses.
"We tend to have the expectation that all of our DNA must be doing something. In reality, only a small part of it is," said Doctor Chris Rands, first author of the study and a former DPhil student in the MRC Functional Genomics Unit at Oxford University.
Only about one percent of human DNA is believed to account for the proteins that carry out most biological processes; the other seven percent is responsible for switching on and off genes that encode proteins.
"There appears to be a lot of redundancy in how our biological processes are controlled and kept in check. It's like having lots of different switches in a room to turn the lights on. Perhaps you could do without some switches on one wall or another, but it's still the same electrical circuit," Ponting said.
