A gene library contains DNA sequences from an organism that have been cloned into vectors for easy analysis and storage. There are two main types of gene libraries: genomic libraries contain fragments of the entire genome, while cDNA libraries contain only coding sequences derived from mRNA. To create a genomic library, genomic DNA is isolated, cut into fragments, and inserted into vectors which are then transferred into bacterial cells. A cDNA library is made from mRNA by reverse transcribing the mRNA into cDNA, which is then inserted into vectors for cloning.

1. Gene Library
For B.Sc III(Semester VI)
(As per the syllabus of S.G.B.A.U.
Amravati)
By : Mohanish V. Wankhade
M.Sc.(Botany),CSIR-NET,SET,GATE

2. •A gene library is the collection of different DNA
sequence from an organism where each sequence has
been cloned into a vector for ease of purification, storage
and analysis.
•There are two types of gene library on the basis of
source of DNA used
•Genomic and c DNA library.

3. Genomic Library
•It is a collection of the complete genome of an
organism
•All fragments of DNA inserted into vector for the
further propagation.
Steps Involved in Genomic Library
• The entire genomic DNA is isolated from donor
cell, purified and broken down into fragments of
correct size for cloning into vector
•The vector isolated from bacterium is also digest
with the same restriction enzymes which used to cut
the DNA

4. •The fragments of DNA are inserted into vectors . Each
vector consists different DNA fragments
•Join the DNA fragments and vectors with enzyme
ligase.
•The recombinant DNA molecules are transferred
into bacterial cell for cloning.

5. cDNA Library
•The library made from complementary or copy DNA
called cDNA library.
•The cDNA library can be constructed using mRNA
because mRNA are highly processed , intron free
representative of DNA having coding sequence.
Steps involved in cDNA library.
•Isolation of mRNA from DNA.
•Synthesis of DNA strand from mRNA by enzyme
reverse transcriptase.
•The mRNA treated with oligo dT primer.
•Four deoxyribose nucleotide triphosphate
dATP,dTTP,dGTP.dCTP. Thus RNA-DNA hybrid is
formed.

6. •RNA –DNA hybrid is treated with terminal transferase and
nucleotide precursor dCTP to form hairpin loop.
•Removal of RNA by using alkaline sucrose solution.
•Synthesis of complementary DNA from single stranded DNA
by the enzyme DNA polymerase.
•Removal of hairpin by the enzyme S1 nuclease.
•Insertion of DNA into vector for cloning.

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