DNA transposons are DNA sequences, sometimes referred to "jumping genes", that can move and integrate to different locations within the genome. They are class II transposable elements (TEs) that move through a DNA intermediate, as opposed to class I TEs, retrotransposons, that move through an RNA intermediate. DNA transposons can move in the DNA of an organism via a single-or double-stranded DNA intermediate. DNA transposons have been found in both prokaryotic and eukaryotic organisms. They can make up a significant portion of an organism's genome, particularly in eukaryotes. In prokaryotes, TE's can facilitate the horizontal transfer of antibiotic resistance or other genes associated with virulence. After replicating and propagating in a host, all transposon copies become inactivated and are lost unless the transposon passes to a genome by starting a new life cycle with horizontal transfer. It is important to note that DNA transposons do not randomly insert themselves into the genome, but rather show preference for specific sites. With regard to movement, DNA transposons can be categorized as autonomous and nonautonomous. Autonomous ones can move on their own, while nonautonomous ones require the presence of another transposable element's gene, transposase, to move. There are three main classifications for movement for DNA transposons: "cut and paste," "rolling circle" (Helitrons), and "self-synthesizing" (Polintons). These distinct mechanisms of movement allow them to move around the genome of an organism. Since DNA transposons cannot synthesize DNA, they replicate using the host replication machinery. These three main classes are then further broken down into 23 different superfamilies characterized by their structure, sequence, and mechanism of action. DNA transposons are a cause of gene expression alterations. As newly inserted DNA into active coding sequences, they can disrupt normal protein functions and cause mutations. Class II TEs make up about 3% of the human genome. Today, there are no active DNA transposons in the human genome. Therefore, the elements found in the human genome are called fossils. Mechanisms of action Cut and paste Traditionally, DNA transposons move around in the genome by a cut and paste method. The system requires a transposase enzyme that catalyzes the movement of the DNA from its current location in the genome and inserts it in a new location. Transposition requires three DNA sites on the transposon: two at each end of the transposon called terminal inverted repeats and one at the target site. The transposase will bind to the terminal