The idiot’s guide to genome sequencing
FOR something that’s caused such havoc around the world the coronavirus is a simple creation – something that allows it to be tracked relatively easily.
The human genome contains more than six billion letters of genetic code.
The coronavirus, however, has just 30,000.
On average up to two of these will mutate randomly each month – a far slower pace of mutation than the influenza or
HIV viruses.
But since the coronavirus replicates itself millions of times inside each infected human there are untold opportunities for mutation to occur.
Already since the start of the pandemic tens of thousands of mutations – most of them inconsequential – have been spotted.
In fact, the virus has mutated so much that the original Wuhan strain has long ago been completely overtaken by new strains leapfrogging each other for survival.
To visualise how these mutations can be tracked via genetic sequencing an expert uses the analogy of a book with 30,000 words.
‘You could regard those RNA [ribonucleic acid] mutations as typos in various different sentences,’ explained Dr Paul Cotter, the head of the Irish Coronavirus Sequencing Consortium.
So a sentence therefore about a cat being in the room takes on a very different meaning if a single letter typo results in ‘cat’ reading ‘rat’. Imagine then that this typo gets repeatedly photocopied and widely distributed.
‘The fact that the sentence differs allows us to track the way the virus is moving around the world,’ Dr Cotter said.
Using a hand-held machine called a sequencer, hooked up to a laptop, scientists can take virus RNA left over from any Covid-19 test and easily read which letters have changed.
This can be done into the past – by reading test samples collected since the start of the pandemic – to trace back to how and where a strain first developed.
It can also be done on a live daily basis to monitor evolving mutations as they spread, Dr Cotter explained.