DNA library or the gene library is the collection of DNA sequences from different organisms. These DNA sequences have been extracted, purified, sequenced and associated with a vector so as to use them for the purpose of analysis, comparative detection etc. Depending on the source of DNA, libraries can be of two types: Genomic libraries- is a collection of the total genomic DNA from a single organism. cDNA libraries-  represents a collection of only the genes that are encoded into proteins by an organism. It is made using mRNA instead of DNA as the starting material.