So our genome is our building blocks. Its a big book of information that tells how to make you. The weird thing is that only 1-1.5% codes for the actual proteins used.
Retroviruses like HIV insert their own DNA into the genome of a cell. So they add themselves into the genome. Thus this cell becomes part human part virus.
When they completely sequenced the human genome, they found that around 1-1.5% genes actually code for proteins and around 8% code for virusses! They are the fossil remnants of ancient retroviruses like HIV, that now are inactivated. They are called human endogenous retroviruses or HERVs. They even resurected a virus from this part in the lab, appropriately called phoenix virus.
Sometimes part of the virus DNA actually gets used for the good. For example one very important reason why we are intelligent is the way we develop in the womb and how efficient the mother can transfer oxygen and nutrients to the child. For that the placenta is used, which is a fascinating and enormous complex organ, especially immunogically. To make it function properly a certain lining of cells have to fuse together to create a membrane of syncytiotrophoblasts.
We utilize a protein called syncitin to do this. We got this protein from viruses. An ancient retrovirus. That is absolutely amazing.
Now what are the positive and negative effects of this viral genome remnants in general? Maybe it plays an important role of autoimmunity, because the immune system must be smelling something weird about these proteins we adopted from viruses. Maybe an important rule in cancer risk.
By the way I think an important thing to note here is that this will probably an extremely rare occurence of humans actually using DNA of retroviruses.
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