noun, plural: DNA transposons
Transposable elements or transposons are small DNA segments capable of replicating and inserting copies of DNA at random sites in the same or a different chromosome. Thus, they are mobile and capable of producing changes in the genome of an organism. In eukaryotes, transposons may be classified as Class I or Class II. In the first class, the transposons is first amplified by transcribing a segment of DNA into RNA, and then reverse-transcribed into DNA. The DNA copy is then inserted at a different site in the genome. In the second class, the transposon moves elsewhere in the genome without going through the reverse transcription.
A DNA transposon is a Class II transposon. The mechanism of transposition involves transposases. In particular, the transposases bind to sites in the DNA (e.g. inverted tandem repeat sequences). The transposases cut a segment of DNA out and form DNA-transposase complex. This complex then inserts the cleaved DNA into a different region of the genome.
In humans, DNA transposons account for about 2% of the genome. 1
1 Lander, E. S., Linton, L. M., Birren, B., et al. (2001). "Initial sequencing and analysis of the human genome". Nature 409 (6822): 860–921.