Transposition is a specialized form of recombination in which genetic elements, such as chromosomal segments, are relocated from one position in the genome to another. These mobile elements are called transposons, or jumping genes.&#160;
Every transposon contains a coding sequence for an enzyme called transposase, in addition to other genes, as well as short flanking sequences that are reverse complements of each other. There are three types of transposition.&#160;
In the first type, known as non-replicative or conservative transposition, the transposase encoding gene produces the dimeric enzyme that cleaves at short inverted sequences that flank a DNA transposon. Then, the inverted sequences come together to form a DNA loop which can be inserted into a target chromosome by transposase-mediated cuts.
In the second type, called replicative transposition, transposase cleaves both the transposon terminals and the target DNA. Then the 3&#8217; ends of the transposon and the 5&#8217; ends of the target DNA are covalently attached in a step called strand transfer.&#160;
This creates an intermediate where the 5&#8217; end of the transposon is still attached to the donor DNA. The unligated ends are used as primers by DNA polymerase to replicate the transposon. This intermediate is called a cointegrate.
Enzymes called resolvases cleave the intermediate at the internal resolution site, generating donor and target DNAs that each have one copy of the transposon.
In the third type of transposition, the transposable element is first transcribed into an RNA intermediate known as a retrotransposon. The RNA is copied back into a DNA sequence by reverse-transcription and then inserted into a target site.&#160;
Despite their different mechanisms, all three of these processes can alter the genomic structure and potentially the function of the target DNA.

<ol>
	<li>Warren, Ian A., Magali Naville, Domitille Chalopin, Perrine Levin, Chlo&#233; Suzanne Berger, Delphine Galiana, and Jean-Nicolas Volff. &#34;Evolutionary impact of transposable elements on genomic diversity and lineage-specific innovation in vertebrates.&#34; Chromosome research 23, no. 3 (2015): 505-531.</li>
	<li>Kapitonov, Vladimir V., and Jerzy Jurka. &#34;A universal classification of eukaryotic transposable elements implemented in Repbase.&#34; Nature Reviews Genetics 9, no. 5 (2008): 411.</li>
	<li>McClintock, Barbara. &#34;Mutable loci in maize.&#34; Carnegie Inst Wash Year Book 47 (1948): 155-169.</li>
</ol>

overview of transposition and recombination

Transposons make up a significant part of genomes of various organisms. Therefore, it is believed that transposition played a major evolutionary role in speciation by changing genome sizes and modifying gene expression patterns. For example, in bacteria, transposition can lead to conferring antibiotic resistance. Movement of transposable elements within the genetic pool of pathogenic bacteria can aid in transfer of antibiotic-resistant genetic elements. In eukaryotes, transposons can carry out regulatory roles by controlling target gene expression under certain physiological conditions, such as stress. In fact, regulation of genes by transposons in response to stress has been widely studied in plants.
Plant genomes provide an excellent model for the study of transposition. The discovery of transposons was made by Barbara McClintock while she was looking into maize cells with broken chromosomes. She discovered that transposition of genetic elements from broken chromosomes causes the color variegation in maize.
Because of the deleterious effects of transposition, transposons rarely move. The frequency of transposition has been correlated with the sequence specifications and structural motifs at the donor and target sites. This low frequency of transposition implies that genetic selection is required to detect the outcomes of transposition. One such outcome, directly dependent on transposition frequency is the presence of white patches on the flowers of Snapdragon plants.

Transposons, Transposition and Recombination

Overview of Transposition and Recombination

Transposons make up a significant part of genomes of various organisms. Therefore, it is believed that transposition played a major evolutionary role in ...