Human-plant hybrid cells reveal truth about dark DNA in our genome
It has been claimed that because most of our DNA is active, it must be important, but now human-plant hybrid cells have been used to show this activity is mostly random noise
Cells containing human and plant DNA reveal something fundamental about our genome
Es sarawuth/Shutterstock
How much of our genome really matters? Some argue that because most of our DNA is active, it must be doing something important. Others say even random DNA would be highly active. This has now been put to the test by studying human cells containing massive chunks of plant DNA, New Scientist can exclusively reveal – and the effectively random plant DNA was indeed nearly as active as human DNA.
The finding shows that a high proportion of genome activity is just noise, rather than having anyn purpose, and thus adds to the evidence that most of the human genome is junk.
“A large amount can simply be explained by background noise,” says Brett Adey at the University of Auckland in New Zealand. “This seems to be broadly consistent with the junk DNA idea.”
The main function of DNA is to store the recipes for making proteins, the molecular machines that do almost all the work in cells. The DNA recipes are copied to make messenger RNAs that carry the recipes to ribosomes, the cell’s protein-making factories.
It was initially assumed almost all DNA consists of recipes for making proteins, but we now know that just 1.2 per cent of the human genome codes for proteins. So what does the rest do?
Since the 1960s, many biologists have argued that it is mostly junk. Yes, a small percentage of non-protein-coding DNA is really important and we are likely to keep discovering bits that do useful things for decades, but such discoveries, they say, won’t change the overall picture of the vast majority of non-coding DNA being junk.
For instance, a 2011 study found that only around 5 per cent of the genome is conserved over deep time – evolution doesn’t seem to care about the rest of it. Biologists in the mostly-junk camp also point out that the size of genomes varies wildly between species. Why does an onion need five times as much DNA as a human, for instance? Why does the lungfish have 30 times as much?
But other biologists have focused on whether human DNA does anything – for instance, whether it gets turned into RNA, even if that RNA has no known purpose. In 2012, a large project called ENCODE concluded that more than 80 per cent of the human genome was active in this sense, and after all. Some biologists in this camp to refer to non-coding DNA, the idea being it is important for reasons we don’t understand yet.