FAMILY OF JUMPING GENES. “Endogenous retroviruses (ERVs) are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. … ERVs are a subclass of a type of gene called a transposon, which can be packaged and moved within the genome to serve a vital role in gene expression and in regulation.”
https://en.wikipedia.org/wiki/Endogenous_retrovirus