What is "endogenous retrovirus"

n. (context biology English) (rfc-def: topic=biology) A retrovirus part of an species' genome through long-ago infection.

Endogenous retroviruses (ERVs) are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. They are abundant in the genomes of jawed vertebrates, and they comprise up to 5–8% of the human genome (lower estimates of ~1%). 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. They are distinguished as retrotransposons, which are Class I elements. Researchers have suggested that retroviruses evolved from a type of transposable gene called a retrotransposon, which includes ERVs; these genes can mutate and instead of moving to another location in the genome they can become exogenous or pathogenic. This means that not all ERVs may have originated as an insertion by a retrovirus but that some may have been the source for the genetic information in the retroviruses they resemble. When integration of viral DNA occurs in the germ-line, it can give rise to an ERV, which can later become fixed in the gene pool of the host population.