Endogenous viral elements are DNA sequences derived from viruses that are ancestrally inserted into the genomes of germ cells. These sequences, which may be fragments of viruses or entire viral genomes (proviruses), can persist in the germline, being passed on from one generation to the next as host alleles.
In some biological systems, endogeneity pertains to the recipient of DNA (usually in prokaryotes). However, because of homeostasis, discerning between internal and external influences is often difficult.
Endogenous transcription factors are those manufactured by the cell, as distinguished from cloned transcription factors.
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The word endogenous