World’s Longest DNA Sequence Decoded

A team of UK scientists have claimed the record for decoding the world’s longest DNA sequence.

DNAThe scientists produced a DNA read that is about 10,000 times longer than normal, and twice as large as a previous record holder, from Australia.
This research has kick-started an Ashes-style competition to sequence an entire chromosome in a single read.

The new holder of the trophy for world’s longest DNA read is a team led by Matt Loose at Nottingham University.

The advance is a technological one – this is about reading the DNA rather than the discovery of a particularly large genome. The DNA used for the long read came from a human.

But the scientists hope the work will make it quicker and easier to sequence genetic information because, currently, DNA has to be chopped up into smaller pieces and then reassembled during the process of sequencing.
Dr Loose’s group also recently produced the most complete human genome sequence using a palm-sized “nanopore” sequencing machine. These potentially offer lower cost and faster processing for DNA sequencing.

He told me: “There has been a competition running to see who can get the longest sequence. I think it is still friendly.”

Dr Loose went on to say: “Australia led for a while, but then we had a read just short of a million. People were then competing to beat the record, in particular to be the first person to get a million-base-pair read.

“The friendly completion launched an Ashes style trophy that is supposed to travel around the world as people get the longest read.”
An Australian team from the Kinghorn Centre for Clinical Genomics was first to pass the million-base milestone.

Making a jigsaw
The technology that enables scientists to read runs of DNA sequences has come a long way since the millennium-era race to decode the first human genome.

In the past 10 or so years, improvements in DNA sequencing technologies have meant that the original billion dollar human genome from 2001 can now be replicated for around $1000.

As costs continue to tumble, there is an expectation that personalised DNA sequencing is not far away. We might soon have our genome decoded during a trip to the doctor’s surgery, or more controversially, our parents might have it read for us, before we are even born.

But one of the remaining stumbling blocks is to put the DNA pieces together in the correct order. Just as it is theoretically possible, but quite unlikely, that a chimpanzee might reproduce a work of Shakespeare with one finger typing, computer programs are unable to re-assemble genomes from short, jumbled DNA sequences.
Dr Loose told me: “There are lots of ways by which you can read DNA, but the problem is that the genetic code, or genome, is often many billions of bases, and so to read them all is very difficult.

“People have used many different ways in the past, but essentially what they do is chop the DNA up into small pieces and then assemble them back together, a bit like what you would do with a jigsaw puzzle.

“You try to get overlapping images so that you can find where the sky is and where the trees are and you can build your picture.”

He explained: “Nanopore sequencing promised lower cost and higher read lengths which means that we can look at interesting organisms which are yet to be sequenced, because their genomes are extraordinarily large.”

Just as the scientists are competing to produce the longest DNA sequence, the technology companies are jostling to become market-leaders in delivering these new advances.

In the future, these methods promise to both revolutionise the understanding of human health, and also bring the same methods to other plants and animals. Long-read DNA sequencing might be used to identify pathogens in foodstuffs, be employed in disease control in animals, used for the diagnosis of infection, and find uses in a vast number of food-related areas.

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