Retroelementit

Retroelementit, also known as retrotransposons or mobile genetic elements, are a type of DNA sequence that can replicate and insert themselves into new locations within a genome. Their defining characteristic is that they are transcribed into RNA, which is then reverse transcribed into DNA by an enzyme called reverse transcriptase, before being integrated back into the genome. This process is reminiscent of the life cycle of retroviruses, and indeed, many retroelements share structural and functional similarities with them.

The majority of retroelements are non-autonomous, meaning they lack the genes necessary for their own mobilization and require the machinery of other retroelements or the host cell to replicate. Autonomous retroelements, on the other hand, encode their own reverse transcriptase and other proteins required for transposition.

Retroelements are abundant in the genomes of eukaryotes, often making up a significant portion of the total DNA. In humans, for example, they constitute approximately 40-45% of the genome. While often considered "junk DNA," retroelements play crucial roles in genome evolution. Their movement can lead to mutations, alter gene expression, and contribute to the formation of new genes and regulatory regions. This dynamic nature has shaped the structure and function of genomes over evolutionary time.