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polar mutationa MUTATION that affects expression not only of the GENE in which it occurs, but also of other genes that lie DOWNSTREAM in the same OPERON (see GENE EXPRESSION). A polar mutation exerts its effect by interfering with TRANSCRIPTION or TRANSLATION of the POLYCISTRONIC mRNA involved. A NONSENSE MUTATION located within a gene may be polar. TRANSPOSABLE GENETIC ELEMENTS carrying transcription and/or translation terminators can also produce polar mutations when they insert into genes.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005