The Southern blot is perhaps one of the oldest methods to analyse DNA and is simply a digest of a sample of DNA which is separated by gel electrophoresis based on size of the fragments generated. Specific DNA target regions are then identified using a nucleic acid probe.
Southern blots are used to identify the presence of the transgene in a digest of the production cellular DNA. Frequently there are multiple copies of the transgene in a production cell line, the Southern blot will identify each target sequence as they are dispersed along the genome or will yield a more intense band where there are more than one insertional sequence positioned adjacent to each other. The southern blot can therefore yield approximate information on the copy number of the transgene. Samples from Master Cell Banks and End of Production Cell Banks can be directly compared on the same blot to demonstrate similarity.
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