Suppression of quinacrine banding of human chromosomes by mounting in organic media.

When A-banded human chromosomes mounted in water are transferred to an organic mounting medium, the chromosomes show uniform bright quinacrine fluorescence. This change is reversible. It is inferred that quinacrine is bound uniformly along the chromosomes, and that Q-banding is a consequence of a non-uniform distribution along the chromosomes of chemical groups, probably proteinaceous, which affect the fluorescence efficiency of the bound quinacrine.