Exon Trapping for Positional Cloning and Fingerprinting

Positional cloning involves the genetic, physical, and transcript mapping of specific parts of a genome (1 ). Linkage analysis can map specific activities, or phenotypes, to a quantitative trait locus (QTL), a genomic region no smaller than 1 centiMorgan (cM) or megabase (Mb) in length. Physical mapping can then provide a map of higher resolution. Physical maps are constructed from clones identified by screening genomic libraries. Genomic clones can be characterized by fingerprinting and ordered to create a contig, a contiguous array of overlapping clones. Transcript identification from the clones in the contig results in a map of genes within the physical map. Finally, expressional and functional studies must be performed to verify gene content.