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| Modern Genetic Analysis Chapter 3. Gene Function Making Functional Transcripts Figure 3-4. Tandemly repeated ribosomal RNA (rRNA) genes being transcribed in the nucleolus of Triturus viridiscens (an amphibian). (rRNA is a component of the ribosome.) Along each gene, many RNA polymerase molecules are attached and transcribing in one direction. The growing RNA molecules appear as threads extending out from the DNA backbone. The shorter RNA molecules are nearer the beginning of transcription; the longer ones have almost been completed. Hence, the "Christmas tree" appearance. (Photograph from O. L. Miller, Jr., and Barbara A. Hamkalo.)

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