Medical Conditions

Nucleotide sequences present in multiple copies in the genome. There are several types of repeated sequences. Interspersed (or dispersed) DNA repeats (INTERSPERSED REPETITIVE SEQUENCES) are copies of transposable elements interspersed throughout the genome. Flanking (or terminal) repeats (TERMINAL REPEAT SEQUENCES) are sequences that are repeated on both ends of a sequence, for example, the long terminal repeats (LTRs) on retroviruses. Direct terminal repeats are in the same direction and inverted terminal repeats are opposite to each other in direction. Tandem repeats (TANDEM REPEAT SEQUENCES) are repeated copies which lie adjacent to each other. These can also be direct or inverted. The ribosomal RNA and transfer RNA genes belong to the class of middle repetitive DNA.