Over the past 10 years great progress has been made in the development of efficient techniques for both gene isolation and mapping. The identifica tion and isolation of transcribed sequences from large chromosomal regions are central to the human genome mapping project. Techniques for isolating novel cDNAs have applications both in the overall construction and integra tion of long-range physical and transcription maps and in the identification of disease genes. A number of different techniques for the isolation of cDNAs from mam malian genomes have been developed, including screening "zoo"...