7.11: 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.