Retrotransposons move by a "copy and paste" mechanism but in contrast to the transposons described above, the copy is made of RNA, not DNA.
The RNA copies are then transcribed back into DNA — using a reverse transcriptase — and these are inserted into new locations in the genome.
Many retrotransposons have long terminal repeats (LTRs) at their ends that may contain over 1000 base pairs in each.
Like DNA transposons, retrotransposons generate direct repeats at their new sites of insertion. In fact, it is the presence of these direct repeats that often is the clue that the intervening stretch of DNA arrived there by retrotransposition.
42% of the entire human genome consists of retrotransposons.
