(i) Genomic Library: This is a collection of clones that represent the complete genome of an organism. For construction of a Genomic library the entire genomic DNA is isolated from host cells or tissues, purified and broken randomly into fragments of correct size for cloning into a suitable vector. 

The major use of Genomic library is hierarchichal shotgun sequencing. cDNA Library : The library made from complementary or copy DNA (cDNA) is called cDNA library. The library represents the DNA of only eukaryotic organisms, not the prokaryotic once. 

cDNA library’ is used to express eukaryotic gene in prokaryotes. cDNA libraries are most usefirl in reverse genetics where the additional genomic information is of less use. It is also useful for subsequently isolating the gene that codes for that mRNA.

(ii) Transformation : In the Biotechnology, Transformation means introduction of rDNA molecules into a living cell. It is the method of transfer of recombinants into the host cells. The DNA molecule comes in the contact of the cell surface and then it is taken up by the host cells. 

Transfection : Transfection is the transfer of foreign DNA into cultural host cells mediated through chemicals. This method is used for the transfer of foreign DNA in the host cell. The recipient host cells are overlayed by this mixture. Consequently, the foreign DNA is taken up by the host cell.