Preparation of cDNA Libraries and Isolation and Analysis of Specific Clones

The development of molecular cloning techniques over the past two decades has generated a powerful arsenal of tools for the study of gene structure and function. It is now possible to synthesize complementary DNA (cDNA) copies of mRNAs from virtually any source and to propagate these cDNAs in vitro in the form of a cDNA library. Initially, cDNA libraries were designed specifically to generate probes for the identification of genomic DNA clones However, the discovery that eukaryotic genes are often composed of coding regions interrupted by introns made it clear that the study of gene expression must include direct analysis of mRNAs and their corresponding cDNAs. Comparison of individual cDNAs to their parent genes and to related cDNAs has since revealed novel mechanisms for the processing of genetic information and has helped to define the primary genetic defects responsible for many disease states.