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Lampbrush chromosome

(Science: cell biology) large chromosomes (as long as 1mm), actually meiotic bivalents, seen during prophase of the extended meiosis in the oocytes of some amphibia.

segments of dna form loops in pairs along the sides of the sister chromosomes, giving them a brush like appearance. These loops are not permanent structures but are formed by the unwinding of chromomeres and represent sites of very active rna synthesis.