DNA Transposons vs. Retrotransposons — What's the Difference?

DNA transposons and retrotransposons represent two distinct classes of mobile genetic elements capable of relocating within a genome. DNA transposons move within the genome through a mechanism that involves excision from one genomic location and integration into another, often described as "cut and paste." This process is mediated by transposase enzymes that recognize terminal repeat sequences in the DNA transposon's structure.

Retrotransposons, in contrast, move through a "copy and paste" mechanism. They are transcribed into RNA, which is then reverse-transcribed into DNA by the enzyme reverse transcriptase. This newly synthesized DNA is integrated into a new location in the genome, resulting in the duplication of the retrotransposon. Retrotransposons are further divided into two main types: LTR (long terminal repeats) retrotransposons and non-LTR retrotransposons, including LINEs (Long Interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements).

While DNA transposons directly move from one place to another within the genome, retrotransposons increase the copy number within the genome each time they transpose, potentially contributing to genomic expansion. DNA transposons are less common in human genomes, whereas retrotransposons make up a significant portion of the human genome.

The transposition activity of DNA transposons is relatively straightforward and does not involve an RNA intermediate, whereas retrotransposons' transposition includes transcription into RNA, reverse transcription into DNA, and then integration. This fundamental difference in their mechanisms of movement reflects their distinct impacts on genome structure and evolution.

In summary, DNA transposons and retrotransposons are key players in genomic diversity and evolution, with DNA transposons employing a simpler transposition process compared to the more complex and copy number-increasing process of retrotransposons.