Abstract

Until quite recently, recombinant DNA technology was not able to deal with DNA molecules larger than 20–40 kb. This is a serious limitation for the study of mammalian, and in particular human genomes whose total length is approx. 3 × 106 kb, since the best resolution of genetic and chromosomal analysis is usually the rough equivalent of 1000–5000 kb. Three recently developed methods promise to bridge this gap: pulsed field gel electrophoresis, which can analyze megabase‐sized DNA fragments; cloning in yeast, which can clone and propagate DNA fragments of several hundred kb; and jumping libraries, which allow ‘jumping’ over large distances along the chromosome. This review presents the current status of these very promising technologies.