1Lecture 18: DNA library and clone identificationWhat is a DNA library?A collection of all DNA of a system, such as the genomic DNA of Arabidopsis, or cDNA of a human organWhy need a DNA library?So we can easily isolate a DNA of interest, such as a gene. A library can be permanently stored and used.•The best way is to clone the DNA fragment into a vector and let a cell replicate the DNA fragment for us. •An alternative way to obtain more copies of the same DNA fragment is to use PCR amplification. The PCR products can also be used as an insert to be cloned into a vector for further amplication of the DNA of interest in cells.(1) The first scenario - we have the known DNA fragment, but want to make more of it
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2(2) The second scenario - we don't have the gene, and want to isolate it(Cloning of a specific gene)In order to isolate a gene, one needs two things: a “DNA library” (genomic library or cDNA library) that is a collection of randomly cloned DNA of an organism, and a "probe" that is a DNA of interest and it must be labeled one way or another. 1. A “genomic library” is a collection of clones (often phage) each contain a piece of genomic DNA of the target organism. Genomic library can be used to isolate any regions of the genome2. A "cDNA library" is a collection of clones (also phage) of different DNA that are copies of the mRNA. So the cDNA library contains only the transcribed regions of the genome. Genomic library and cDNA library