In situ hybridization and pulsed-field gel analysis define two major minisatellite loci: 1q23 for minisatellite 33.6 and 7q35-q36 for minisatellite 33.15.

The two classical minisatellite probes, 33.6 and 33.15, were used for in situ hybridization to human metaphase chromosomes. Surprisingly, a single major hybridization peak was observed with each probe, respectively at 1q23 for 33.6 and 7q35-q36 for 33.15. Hybridization to human DNA cleaved with "rare-cutter" enzymes and fractionated on pulsed-field gels also showed a fairly simple, largely monomorphic pattern which allows chromosomal assignment using somatic cell hybrids. Differences in hybridization stringency and degree of resolution account for most of the discrepancy between these results and the accepted view of minisatellites, i.e., a large number of unlinked loci spread over the genome. Our results nevertheless indicate the existence of particularly large and homologous loci on a particular chromosome for each of these probes.