participates in the ability to distinguish between maternal and paternal DNA fragments. This phenomenon is known as “genomic imprinting”.
TRANSPOSABLE DNA Transposable DNA or “jumping genes” represent genes that can jump from one place on the genome to another. Both prokaryotes and eukaryotes have transposable DNA; they make up about half of all the human genome and as much as 90 percent of the genome of the corn plant. There are many different types of transposable DNA, which are also called transposons. Some of them require what’s called reverse transcription, which is the transcription of RNA into DNA in order to be transposable, while others do not require this. Those that require reverse transcription are called retrotransposons or class 1 transposons, while those that don’t are called class 2 transposons. Class 2 transposons code for the protein known as protein transposase, which is necessary for insertion and excision of DNA. These always move on their own using cutting and pasting; they do not require RNA to be able to move. Class 2 transposons have terminal inverted repeats that are up to 40 base pairs in length on both ends of the sequence. These terminal inverted repeats are recognized by transposase. There are also direct repeats that aren’t a part of the transposable element but are important in the insertion of the transposon. The repeats are actually left behind after excision of the element. About 2 percent of human genes is made from class 2 transposons. The rest of the transposable elements are class 1 transposons. As mentioned, class 1 transposons need an RNA intermediary. They do not code for transposase but make RNA transcripts, using reverse transcriptase to turn this RNA into DNA that gets inserted into a different part of the genome. Either type of transposable DNA can be autonomous or nonautonomous. The autonomous transposable elements can move on their own, while nonautonomous transposable elements require other transposable elements in order to move. The
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