Fishing for complements: finding genes by direct selection.

Deriving a saturated gene map of a complex genome is a daunting undertaking. By current methods, finding all the genes in even a single megabase of the human genome is technically difficult. Direct selection is a technique focussed upon the isolation of cDNAs encoded by such large genomic regions and involves hybridization-based selection and PCR methods. It is particularly useful in the positional cloning of loci associated with genetic disease and for rapidly searching large genomic regions for transcriptional units that are normally expressed at low levels. Direct selection can produce up to 100,000-fold enrichment of specific cDNAs, and allows simultaneous searches to be conducted on many complex tissues. The applications of this technique extend to many approaches that involve cDNA cloning, including isolating related genes from complex pools of cDNA.