There are two types of gene library:
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Genomic Library: is the collection of cloned DNA segments that represents an entire genome of an organism.
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It contains total nuclear DNA of an organism or species.
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This cloned DNA segments are cut by the enzyme restriction endonuclease and then inserted into specific vectors.
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It contains whole genomic fragments such as gene exon and introns, gene promoters, intragenic DNA, origin of replication, etc.
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The below figure explains construction of library:
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cDNA Library: is the collection of complementary DNA produced from mRNA that is present in nucleus.
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In the eukaryotes, formation of cDNA from mature mRNA is done by reverse transcriptase enzyme.
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This library contains single stranded DNA.
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It is an important tool for the study of molecular hybridisation and cloning technology.
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The below figure explains construction of cDNA library:
