Our personal genomes (the genetic information of an organism) are littered with the remnants of viruses that infected our ancestors.
But fear not. These viruses aren’t infectious, like the ones that cause COVID-19 or the common cold, but rather sequences that have silently become integrated into our DNA over millions of years.
Most of them come from a subset of viruses called retroviruses, which infect host cells and then trick them into making the proteins that they need to replicate.
Occasionally, a retrovirus will embed itself into a sperm or egg cell, and when that happens it can hitch a ride to the next generation (and beyond).
Although this is a rare event, across large, evolutionary spans of time, the numbers build up. Today, it’s estimated that around eight per cent of our DNA is made up of these viral relics.
For a long time, researchers thought that these viral sequences were of little consequence, so-called ‘junk DNA’ that just hung around inside our cells where it didn’t code for anything meaningful.
In recent years, this view has changed. Modern-day descendants of these viral proteins have been shown to play a role in storing memories, in the development of the placenta and in the immune system’s ability to fend off disease-causing microbes.
It’s not all good news, however. Some viral DNA fragments have been linked to human diseases, including amyotrophic lateral sclerosis (ALS), some cancers and type 1 diabetes.
On their own, they’re not enough to cause the disease, but they can play a part in the intricate biology that unravels.
This article is an answer to the question (asked by Nick Conley, via email) 'Could a virus change my DNA?'
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