Sequencing the human genome with handheld technology
A machine the size of a mobile phone has sequenced the entire human genome, filling in some of the gaps in our knowledge
Inside each one of your cells, two metres of DNA is tightly wrapped up into a space just a hundredth of a millimetre across. It acts like an instruction manual, telling each cell how to make the right proteins at the right times. This DNA, in its entirety, is called your genome, and it’s a chain of smaller sub-units called bases: As, Ts, Cs, and Gs. The human genome is about 3 billion bases long, and it’s the sequence of these bases that determines the function of each gene.
The process of mapping the human genome was one of the greatest undertakings in scientific history. Termed “The Human Genome Project”, it began in 1990 and took over 13 years – costing billions of Pounds.
Since then, sequencing technology has greatly improved and scientists are able to sequence a person’s genome in a matter of days and for only a few thousand Pounds. However, this process still involves large, expensive machines which require specialist training. Now, publishing their work in Nature Biotechnology, researchers have managed to sequence a human genome using a machine the size of a mobile phone.
The machine, made by Oxford Nanopore, is called the MinION. To sequence DNA, a solution of DNA is put onto a membrane with lots of tiny holes. An electrical current is applied, which causes the DNA to squeeze through those holes. As each DNA letter (A, T, C or G) "pops" through the hole in the membrane, it temporarily alters the current in a highly distinctive way unique to each base. These interruptions can be interpreted by computer software to yield the DNA sequence in real-time.
Most other sequencers cut up the DNA into tiny fragments of just a few hundred bases long to be sequenced. The computer then has to spend sometimes hours or even days piecing these short sequences back together, and the assembly isn’t always accurate. The MinION, on the other hand, can sequence fragments which are hundreds of thousands of bases long, cutting down the computing time and the error rate considerably.
This means that as well as being the first portable device to sequence an entire human genome, it has also managed to sequence several large regions of the genome which we’ve only ever been able to reconstruct from shorter sequences. These include important parts of the genome, like the telomeres found at the ends of chromosomes and which are important in cancer and ageing; also the major histocompatibility complex, that's essential for the immune system, has now finally been sequenced in full.
Because of its size and ability to sequence DNA in real-time, the MinION was taken to West Africa during the Ebola outbreak in 2014 to sequence the virus of patients with the disease. The ability to identify a virus quickly could greatly improve survival rates, and now that this technology is capable of sequencing human genomes (which are much larger than those of viruses) it could even be used to sequence cancer tumours in order to determine the most effective treatment.
“When the device was initially released, nobody thought we would be able to get anywhere close to a human genome,” explains Nottingham University’s Matt Loose, one of the researchers involved in the project. “But we’ve now shown that it can be done.”