From Rod Tranchant
About a tenth of the human genome “remains impossible to sequence with existing methods”, Anna Gosline writes (5 July, p 36). I thought the whole thing had been sequenced; this is the first I’ve heard of this.
Surely DNA is DNA, so if some can be done all can be done. What’s the problem?
The editor writes:
• All existing methods work by breaking genomes into tiny pieces, sequencing those pieces and reassembling the resulting “jigsaw”. The trouble is that the human genome is highly repetitive. Some parts – mainly the middle and ends of chromosomes – are so repetitive that it’s impossible to reassemble the jigsaw. Nanopore sequencing, in which a DNA sequence is read off as a strand passes through a pore, might overcome this problem but this technology is still at a very early stage.
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