Structural Biochemistry/DNA recombinant techniques/Genomic Library
Genomic libraries are a catalog of genes of a particular organism. They are also commonly referred to as gene banks. To create a genomic library, the complete genome of an organism is cleaved into fragments and inserted into a cloning vector. It can also refer to the collection of vector molecules.
How to Create a Genomic Library 
First, a variety of restriction endonucleases are used to cleave at certain base pairs to create the necessary fragments of the DNA. These restriction endonucleases are chosen in such a way that the cohesive ends are compatible with a cloning vector and that the complete genome is represented by these fragments. This also means that the cloning vector is cleaved with the same restriction endonucleases and the original fragments are combined with the cloning vector using a ligase. This mixture is then inserted into a bacterial cell to produce a library. Each cell will have a different DNA molecule. Ordering of individual clones is archived by identifying overlapping sequences. This set of overlapping sequences of the catalog is defined as a contig.
Roles of Genomic Library 
With complete information in the library for a specific organism, researchers can perform a variety of experiments on the DNA. By doing so, they can determine the actions and interaction of separated genes along the strand. Also, they can compare the genomic library of healthy and unhealthy individuals of the same species to see where differences in genetic coding may be led to unexpected mutations.
In physical reality, a genomic library for humans is a collection of bacteria, the most common one is E. coli. The usable sequence of DNA from the human genome gets transferred and carried through the E. coli. The DNA is prepared by digesting it with a restriction enzyme. Then the target segments are inserted into the bacteria by using lamba phage.This creates a basic unamplified library, where the bacteria have been allowed to multiply and create additional copies of each section of the DNA.