A genomic DNA library is made up of an organism’s total genomic DNA information. It is constructed by cloning the entire genome of a cell in the form of random and unidentifiable clones. The chain termination method is used to sequence the DNA molecules. These are the steps used to construct a genomic library from a large genome:

1. DNA is extracted and purified. 
2. The purified DNA is digested with a restriction enzyme to create similar-sized fragments, each containing one or more genes. 
3. The DNA fragments are inserted into vectors that were cut using the same restriction enzymes. 
4. The enzyme DNA ligase is used to seal the DNA fragments into the vector, creating a large number of recombinant molecules. 
5. The host bacterium takes up the recombinant molecules by transformation, creating a genomic DNA library.