Dye binding mechanisms in G-banding of chromosomes

The mechanisms whereby Giemsa is bound to chromosomes to produce G-banding patterns have been studied. The magenta colour produced in chromosomes by Giemsa staining appears to be due to the same 2:1 thiazine-eosin compound that precipitates from Giemsa solutions. This precipitate is formed in chromosomes in regions in which DNA phosphates occur at the correct distance apart to bind two thiazine molecules, which are subsequently able to bind to the same eosin molecule. Banding appears to be produced as a result of this precipitation occurring preferentially in hydrophobic regions of chromosomes.