Cistron(redirected from functional gene)
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a unit of genetic material responsible for a single function. The term “cistron” was introduced by the American geneticist S. Benzer in 1957 together with the terms “recon”—the smallest unit of deoxyribonucleic acid (DNA) capable of recombination—and “muton”—the smallest unit of DNA in which a change can result in a mutation. Benzer hypothesized correctly that all three units are sections of the nucleic acid molecule that differ from one another in length. In size the cistron is equal on the average to 1,200 nucleotides, with the number of nucleotides generally varying from 400 to 4,000. In modern genetics, a cistron is generally defined as the unit in nucleic acid that codes the structure of a single polypeptide. Consequently, the terms “cistron” and “gene” are synonymous.