system
Given the following post, respond as if you're commenting on Reddit:
human
How do scientists know that a specific part of our DNA is viral?

Just reading about virus evolution, and it got me wondering about all the times scientists say some 5-10% of our DNA is viral in origin. If those genes are potentially still active in us--not sure if they're non-coding or not--how do they know it's viral (and/or not the other way around)? (Not that I don't believe the much-smarter-than-me scientists, I'm just curious)

Thanks (and sorry if I misused vocabulary)!
gpt
Very cool question!

The sequences you’re referring too are called “endogenous retroviruses.” We know they’re viral in origin due to how similar they are in nucleic Acid sequence and sequence element types to known and current retroviruses.

To answer some of your question about activity, different sites are transcribed at varying levels. Some even have direct impact on biological function of other human genes.

But to date none have been identified that are still capable of producing an infectious virus, as far as I’m currently aware. 

Did that answer your questions?