Chromosomal Localization of Genes Through Pulsed-Field Gel Electrophoresis Techniques

The development of electrophoretic techniques for separating intact chromosomal DNA from lower eukaryotes has provided a powerful system for analyzing the karyotypes of these organisms. Before the advent of pulsed field gel electrophoresis (1 ), the study of lower eukaryotic chromosomal organization, by conventional genetic and cytogenetic methods, had proven to be unproductive, but now the genome of these organisms can be analyzed with relative facility. Electrophoretic karyotypes have been determined for filamentous fungi such as Aspergillus nidulans (2 ), Mucor cirinelloides (3 ), and Schizophyllum commune (4 ), and for yeasts such as Schizosaccharomyces pombe (5 ,6 ) and Saccharomyces cerevisiae . These chromosomal separations by pulsed-field gel electrophoresis (PFGE) have, of course, allowed sizing of individual chromosomes and hence the nuclear genomes of these species, usually using the chromosomes of S. cerevisiae and S. pombe as size markers (see Chapter 8 , by J. R. Johnston), but they have also enabled cloned genes to be assigned to their chromosomes by hybridization with suitable labeled probes, so bypassing the much more laborious procedures of conventional genetic mapping.