of new genes. TEs may also have been co-opted by the vertebrate immune system as a means of producing antibody diversity. The V(D)J recombination system operates by a mechanism similar to that of some TEs. TEs also serve to generate repeating sequences that can form dsRNA to act as a substrate for the action of ADAR in RNA editing. TEs can contain many types of genes, including those conferring antibiotic resistance and the ability to transpose to conjugative plasmids. Some TEs also contain integrons, genetic elements that can capture and express genes from other sources. These contain integrase, which can integrate gene cassettes. There are over 40 antibiotic resistance genes identified on cassettes, as well as virulence genes. Transposons do not always excise their elements precisely, sometimes removing the adjacent base pairs; this phenomenon is called exon shuffling. Shuffling two unrelated exons can create a novel gene product or, more likely, an intron. Some non-autonomous DNA TEs found in plants can capture coding DNA from genes and shuffle them across the genome. This process can duplicate genes in the genome (a phenomenon called transduplication), and can contribute to generate novel genes by exon shuffling. Evolutionary drive for TEs on the genomic context There is a hypothesis that states that TEs might provide a ready source of DNA that could be co-opted by the cell to help regulate gene expression. Research showed that many diverse modes of TEs co-evolution along with some transcription factors targeting TE-associated genomic elements and chromatin are evolving from TE sequences. Most of the time, these particular modes do not follow the simple model of TEs and regulating host gene expression. Applications Transposable elements can be harnessed in laboratory and research settings to study genomes of organisms and even engineer genetic sequences. The use of transposable elements can be split into two categories: for genetic engineering and as a genetic tool. Genetic engineering Insertional mutagenesis uses the features of a TE to insert a sequence. In most cases, this is used to remove a DNA sequence or cause a frameshift mutation. In some cases the insertion of a TE into a gene can disrupt that gene's function in a reversible manner where transposase-mediated excision of the DNA transposon restores gene function. This produces plants in which neighboring cells have different genotypes. This feature allows researchers to distinguish between genes that must be present inside of a cell