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Amplification is the temporary synthesis of extra, functional copies of some genes, in vivo or in vitro, by some forms of the polymerase chain reaction. Bacteriophage l can be amplified by a series of nitrocellulose filter transfers after in situ hybridization. The addition of chloramphenicol (10–20 μg/mL) to pBR322 and pBR327 may amplify plasmid yield, if the synthesis of protein is not completely prevented. Cosmid libraries may be amplified by starting on solid plates followed by liquid cultures. Replica-plating can amplify animal cell cultures. Approximately 5 × 104 colonies can be accommodated on a 138-mm filter, and this way about 30 filters are required to obtain a representative library of overlapping fragments. DNA amplification can occur in a genetically programmed and predetermined manner in eukaryotes. For example, in the ovarian follicle of Drosophila, large quantities of an egg-shell protein is needed during oogenesis. The need is met by a disproportionately favorable repl ...