A gene library is a collection of different DNA sequences from an organism, which has been cloned into vectors for ease of purification, storage, and analysis. There are two types of gene libraries based on the availability of a source of DNA used. The genomic library contains DNA fragments that represent the entire genome of an organism, whereas CDNA libraries will contain only the complementary DNA molecules synthesized from the mRNA molecules in a cell. For the construction of gene libraries, we have to know the size of the gene and insert size or capacity of vectors. Vectors used for gene library construction are plasmid, lambda phage, Cosmid, bacterial artificial chromosome, and yeast artificial chromosome. The most commonly used vector type is lambda, but most genomic libraries are constructed using BAC and YAC vectors. For the construction of gene libraries, the steps followed are the isolation of bacteria followed by cloning and sequencing DNA. The main use of genetic libraries is to increase the likelihood that a particular portion of a DNA source will be found within the collection. It is used to collect and store information as a set of DNA molecules. Gene libraries are stored inside bacterial cells. Bacterial colonies have the ability to store different genes, similar to how books are stored in a library.
