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discrete DNA sequences of nucleotides that are repeated at various sites on bacterial chromosomes, certain plasmids, and bacteriophages and that can move from one site to another on the chromosome, to another plasmid in the same bacterium, or to a bacteriophage.
insertion sequence (IS) a type of TRANSPOSABLE GENETIC ELEMENT that codes for its own transposition but which apparently carries no other genetic information. Generally it is several hundred base pairs in length. It is capable of causing MUTATION when it inserts into a GENE. Insertion sequences may exist as independent entities or may form the terminal parts of certain TRANSPOSONS.