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A transposable element (TE or transposon) is a DNA sequence that can change its position within the genome, sometimes creating or reversing mutations and altering the cell's genome size. Transposition often results in duplication of the TE. Barbara McClintock's discovery of these jumping genes earned her a Nobel prize in 1983. TEs make up a large fraction of the C-value of eukaryotic cells. There are at least two classes of TEs: class I TEs generally function via reverse transcription, while class II TEs encode the protein transposase, which they require for insertion and excision, and some of these TEs also encode other proteins. It has been shown that TEs are important in genome function and evolution. In ''Oxytricha'', which has a unique genetic system, they play a critical role in development.〔(【引用サイトリンク】title='Junk' DNA Has Important Role, Researchers Find )〕 They are also very useful to researchers as a means to alter DNA inside a living organism. == Discovery == Barbara McClintock discovered the first TEs in maize, ''Zea mays'', at the Cold Spring Harbor Laboratory. McClintock was experimenting with maize plants that had broken chromosomes. In the winter of 1944–1945 McClintock planted corn kernels that were self-pollinated, meaning that the flowers were pollinated by the silk of their own plant.〔 These kernels came from a long line of plants that had been self-pollinated, causing broken arms on the end of their ninth chromosome.〔 As the maize plants began to grow, McClintock noted unusual color patterns on the leaves.〔 For example, one leaf had two albino patches of almost identical size, located side by side on the leaf.〔 McClintock hypothesized that during cell division certain cells lost genetic material, while others gained what they had lost. However, when comparing the chromosomes of the current generation of plants and their parent generation, she found certain parts of the chromosomes had switched positions on the chromosome.〔 She disproved the popular genetic theory of the time that genes were fixed in their position on a chromosome. McClintock found that genes could not only move, but they could also be turned on or off due to certain environmental conditions or during different stages of cell development.〔 McClintock also showed that gene mutations could be reversed. McClintock presented her report on her findings in 1951, and published an article on her discoveries in ''Genetics'' in November 1953 entitled, ″Induction of Instability at Selected Loci in Maize.″ Her work would be largely dismissed and ignored until the late 1960s-1970s when it would be rediscovered after TEs were found in bacteria. She was awarded a Nobel Prize in Medicine or Physiology in 1983 for her discovery of TEs, more than thirty years after her research and initial discovery.〔 〕 Approximately 90% of maize genome is made up of TEs, and 50% in the human genome. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Transposable element」の詳細全文を読む スポンサード リンク
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