New study suggests only 8.2% of our DNA is functional
Posted by: Deepak Kumar
Controversial new research claims that only a
small fraction of the human genome is actually
doing something important. Over the years, there's been plenty of back and
forth over how much of our DNA is important -
for decades much of it was thought of as “junk
DNA”, but geneticists have gradually come to
believe that some of these seemingly pointless
segments of DNA may be crucial to regulating the
rest of the genome.
Importantly, researchers from the Encyclopedia of
DNA Elements (ENCODE) in 2012 stated that
about 80 percent of human DNA has some kind
of “biochemical function” as Sci-News reports.
The study was controversial, because many
researchers argued that the definition of
"biochemical function" was too broad, and that
just because activity occurs on the DNA, it
doesn’t necessarily mean that it has a function.
Of course, how do you test the impact that each
segment of DNA has on the body?
The new study, led by Gerton Lunter from the
University of Oxford's Wellcome Trust Centre for
Human Genetics in the UK, builds on this
research. In order to work out which DNA
segments are actually funtionally useful, they
looked at how it's changed over the past 100
million years of mammalian evolution - and found
that only 8.2 percent of our DNA was important
enough to stay the same.
They came to this conclusion by comparing the
DNA of various mammals, such as mice, guinea
pigs, rabbits and horses, and looked at which
chunks of DNA were conserved across different
species. The idea is that if a big segment of DNA
has been conserved over 100 million years of
evolution, despite countless natural mutations,
then it must have a pretty important function.
“Throughout the evolution of these species from
their common ancestors, mutations arise in the
DNA and natural selection counteracts these
changes to keep useful DNA sequences intact,”
Lunter told Sci-News.
To find which areas stayed the same, the
scientists actually looked for the pattern of
insertions and deletions of chunks of DNA in the
sequence. These should generally occur pretty
randomly along a genome - unless natural
selection had acted to keep a stretch of important
DNA as it is, in which case there would be wider
gaps between these insertions and deletions.
“We found that 8.2 percent of our human genome
is functional," Lutner told Sci-News . "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."
Chris Rands from the University of Oxford, who
was the first author of the paper published in
PLOS Genetics, added 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," he told Sci-News .
The other 7 percent is most likely involved in
switching on and off the genes that encode those
proteins, like regulatory bodies.
And the other 91.8 percent? Generally, it’s pretty
lazy.
“The rest of our genome is leftover evolutionary
material, parts of the genome that have
undergone losses or gains in the DNA code,” said
Lutner.