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Essay

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In cell-based DNA cloning a key step is ____ 1____ , the stage when the DNA of interest enters the provided host dells. The ____1______ efficiency is usually very low, but when ____ 1____ occurs just a ___2____ DNA molecule usually enters the cell. As a result, a complex starting DNA population can be fractionated by the cells (which effectively act as sorting offices). A second key step allows identification of ____3_____ cells (in the case of bacteria, the host cells are genetically modified to be sensitive to some ____4____ , and the vector carries a gene conferring ____5____ to the ____4____ ) . Many of the transformed cells contain just the vector DNA instead of the desired ____5____ DNA. To identify a specific ____5____ DNA, a more specific assay is required that often involves ____6_____ using a closely related labelled DNA or RNA ____7____.