A reverse transcriptase (RT) is an enzyme used to generate [[complementary DNA]] (cDNA) from an [[RNA]] template, a process termed [[reverse transcription]]. Reverse transcriptases are used by [[retrovirus]]es to replicate their [[genome]]s, by retrotransposon mobile genetic elements to proliferate within the host genome, by eukaryotic cells to extend the [[telomere]]s at the ends of their linear chromosomes, and by some non-retroviruses such as the [[hepatitis]] B virus, a member of the Hepadnaviridae, which are dsDNA-RT viruses.