polyteny

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polyteny The condition of a chromosome, nucleus, or cell in which the DNA has repeatedly replicated, without subsequently separating (see endomitosis). This results in a cablelike giant chromosome, consisting of up to 1000 parallel chromatids and often showing conspicuous transverse banding. Polyteny has been observed in the cells of certain insects of the order Diptera, notably in the salivary glands of Drosophila. Swellings (called puffs) have been observed in giant chromosomes at specific stages in the development of these insects. Puffs are associated with messenger RNA and are sites of gene transcription.