Enhancement of banding patterns in human metaphase chromosomes by energy transfer

Intermolecular energy transfer between appropriately chosen pairs of dyes can be used to induce or enhance banding patterns in human metaphase chromosomes. Energy transfer, calibrated by fluorometric studies on soluble dye.DNA complexes, can also be detected by photometric measurements on cytological preparations of metaphase chromosomes stained with pairs of fluorochromes. If a fluorescent dye with one type of binding or quantum yield specificity (e.g., quinacrine, 33258 Hoechst, or chromomycin A(3)) is employed together with a counterstain (e.g., actinomycin D, 7-aminoactinomycin D, or methyl green) exhibiting a complementary base pair binding specificity and satisfying spectral overlap criteria for energy transfer, contrast in fluorescence from the first dye is enhanced in specific subsets of standard chromosome bands. Extensive energy transfer presumably suppress donor fluorescence except in chromosomal region containing clusters of at least 20 base pairs predominantly of one type, within which the donor but not the acceptor can bind and fluoresce. Quinacrine-bright polymorphic regions are especially resistant to fluorescence quenching by counterstains with G.C binding specificity, strengthening the evidence that these latter regions are highly enriched for A.T base pair clusters. The ability to highlight selectively many such polymorphic regions may prove of further, practical, utility in a number of cytogenetic problems.