AbstractPhenomena studied by fluorescence spectroscopy, including differential perturbations of dye fluorescence by variations in DNA composition and interdye energy transfer, can be applied to cytological studies of chromosome structure, replication, and repair. When combined with fluorescence‐activated flow sorting, fluorescent differentiation between metaphase chromosomes can be exploited to obtain recombinant DNA libraries enriched for all or parts of individual chromosomes. Cloned DNA segments from such libraries continue to find application in studies of human chromosome structure and function and in molecular linkage analyses, thus leading to molecular genetic investigations of human disease state