• Question: If you feel a bit viral approximately what percentage of your DNA is derived from viruses that invaded your ancestors’ genomes?

    Asked by Ayse to Tristan, Sophie, Ravinder, Matt, Barbara on 9 Mar 2015.
    • Photo: Sophie Robinson

      Sophie Robinson answered on 9 Mar 2015:

      About eight percent of our DNA originally came from viruses. At some point, one of our ancestors will have been affected by a virus which inserted its DNA into their reproductive cells. This DNA was then passed on from parent to offspring and now everyone derived from that person has this viral DNA in their genomes. Sometimes when a virus inserts its DNA into our genome, it can damage our own genes and lead to cancer. This is what happens with the HPV virus to lead to cervical cancer.

    • Photo: Tristan Smith

      Tristan Smith answered on 9 Mar 2015:

      Interesting question, If you feel viral, you probably have caught a cold or other infectious virus. Most infectious viruses do not infect a person’s DNA, only very rare virus, such as HIV and other retroviruses have the ability to ‘integrate’ into your genome. However, there are lots of transposons in the human genome, maybe as much as 5% and they are left over from ancient retroviruses (not HIV!!!), some may have useful things on them but most just sit there and do nothing.
      Also, they are not left over from ancestors like Lucy or Neanderthals, they go back farther than that, as far back as the jaw evolved in fish actually. So even if the same retrovirus is around today, it probably only affects fish and would do nothing to us.

    • Photo: Matthew Moore

      Matthew Moore answered on 12 Mar 2015:

      The human genome, as Sophie and Tristan have mentioned, is actually littered with ‘viral’ DNA (at what point does it become our DNA?). Viruses integrate their DNA (or RNA via reverse transcription) and it can become inherited if it makes it into the germline.

      These vary, some as mentioned ‘endogenous retroviruses’ can jump around the genome and even cause cancers if they jump into a gene (particuarly one involved in DNA repair) –but don’t worry the genome is massive and only a few percent of it contains your genes so this is unlikely.

      Many have lost the ability to move around as such and are instead fossils of ancient virus interactions with your genome!

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