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How do scientists use a DNA library to locate a specific gene?
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recombinant DNA
The process of DNA extraction is necessary to isolate molecules of DNA from cells or tissues. A series of steps, including the use of protease enzymes to strip proteins from the DNA, are required for isolating pure DNA that is suitable for use in later procedures, such as cloning or sequencing.
To locate a specific gene within a DNA library, scientists typically use a process involving a labeled probe that shows homology to the target gene.1
The procedure is generally conducted as follows:
- Preparation: Bacterial colonies containing the library are grown on Petri dishes. A porous membrane is placed over the colonies, causing cells to adhere to it.1
- Denaturation: The cells on the membrane are ruptured, and the DNA is separated into single strands.1
- Probing: A DNA segment known to be homologous to the target gene is labeled—often with radioactive phosphorus—and also separated into single strands. The membrane is bathed in a solution containing this probe.1
- Detection: The single-stranded probe adheres only to the DNA of the clone containing the equivalent gene. When the membrane is placed against radiation-sensitive film, the location of the desired clone is revealed by a black spot.1
Once identified, the specific clone can be retrieved from the original Petri dishes for further study or manipulation.1