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From where we get our gene of interest for gene cloning? one of the source is genomic library, other source is cDNA library. In this video let us understand what is genomic library? genomic library as the term indicates it is a library or collection of cloned DNA fragments of an organism. It represents an entire genome of individual animal plant bacteria or virus understudy or it's a collection or library of cloned segments of DNA containing at least one copy of every gene from a particular organism. Let's take an example to understand the concept of genomic library construction of genomic library of a phage. Phages are viruses that attacks bacteria so this is a bacteriophage so we are going to construct the genomic library of this phage. First we need to isolate the DNA so suppose this is the DNA of the phage it is a very small genome then we need to cut this isolated DNA using suitable restriction enzyme into suitable sized fragments so these are the fragments a,b,c,d,e so these are the genes of the phage, only five genes now what we do next is, incorporate these fragments into a suitable vector like plasmid, cosmid etc so I have introduced this each gene into different plasmid vector so you can see the color a b c d and e so we have incorporated the gene fragment in the suitable vector as we discussed in the previous video we will be using restriction enzymes and ligases for making this recombinant vector now we have plasmid vector with our DNA fragment next step is introduction of this recombinant plasmid into suitable hose like bacterium that is followed by multiplication screening and identification characterization of clones or colonies that contain these genes. so after screening and characterization we have colonies with a gene, b gene, c gene, d gene and e gene. So these as this is a plasmid this will replicate inside the bacteria so many copies of that particular gene is there as colonies of bacteria so this is colony containing the a fragment or a gene and this is a colony containing the b fragment or b gene as c fragment or c gene and this is d fragment or d gene and finally we have e gene so this collection of cloned DNA fragments that is maintained is called genomic library of this phage. Let me repeat this phage has five genes and these five genes are maintained as bacterial colonies containing cloned DNA fragment. This maintenance of set of clones is called as genomic library, for an experiment if I require c gene, then I will be isolating c gene from this particular colony, that is from genomic library. In short genomic library represents cloned DNA fragments of an organism that is maintained as colonies. Let me summarize the steps in the construction of genomic library, first we need to isolate the genome DNA from cell under study, it can be from virus, bacteria, animals, plant cells etc. Then cutting isolated DNA using suitable restriction enzyme into suitable sized fragments, then incorporation of these fragments into a suitable vector, Screening, identification and characterization of clones after transformation experiment or introduction of this vector into a suitable host and finally maintenance of such set of clones containing cloned DNA fragments of that particular organism under study is called genomic library, the source of our gene of interest is this genomic library.