Only 8.2 per cent of human DNA is 'functional'

Written by PTI | London | Updated: Jul 25 2014, 21:04pm hrs
Dna The scientists' idea was to look at where insertions and deletions of chunks of DNA appeared in the mammals' genomes.(Thinkstock)
Only 8.2 per cent of human DNA is doing something important or is likely to be 'functional', Oxford scientists say.

This figure is very different from one given in 2012, when some scientists involved in the ENCODE (Encyclopedia of DNA Elements) project stated that 80 per cent of our genome has some biochemical function.

Many in the field have argued that the biochemical definition of 'function' was too broad - just because an activity on DNA occurs, it does not necessarily have a consequence; for functionality you need to demonstrate that an activity matters.

To reach their figure, the Oxford University group took advantage of the ability of evolution to discern which activities matter and which do not.

They identified how much of our genome has avoided accumulating changes over 100 million years of mammalian evolution - a clear indication that this DNA matters, it has some important function that needs to be retained.

The researchers used a computational approach to compare the complete DNA sequences of various mammals, from mice, guinea pigs and rabbits to dogs, horses and humans.

The scientists' idea was to look at where insertions and deletions of chunks of DNA appeared in the mammals' genomes.

These could be expected to fall approximately randomly in the sequence - except where natural selection was acting to preserve functional DNA, where insertions and deletions would then lie further apart.

Researchers found that only 8.2 per cent of our human genome is functional.

The rest of our genome is leftover evolutionary material, parts of the genome that have undergone losses or gains in the DNA code - often called 'junk' DNA.

"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 Dr Chris Rands, first author of the study.

Not all of the 8.2 per cent is equally important, the researchers said.

A little over 1 per cent of human DNA accounts for the proteins that carry out almost all of the critical biological processes in the body.

The other 7 per cent is thought to be involved in the switching on and off of genes that encode proteins - at different times, in response to various factors, and in different parts of the body.