CT banding of human chromosomes. The role of cations in the alkaline pretreatment.

This paper describes a study of the role of certain cations in the alkaline pretreatment step used in the CT technique for chromosome band formation. Treatment of human chromosomes with ammonium bases or with the hydroxides of the monovalent alkali metals Na, K, or Li resulted in their rapid disintegration, unless very short treatment periods or diluted solutions were used. In the latter cases a subsequent staining produced a weak G-banding pattern. The chromosomes appeared to be much less sensitive to treatment with the hydroxides of the divalent alkaline earth metals Ba, Sr, Ca, and Mg. Staining after exposure to these hydroxides yielded R-banding patterns. The reduced alkali sensitivity of the chromosomes and the reverse banding pattern formation observed are probably the result of a chromatin stabilization by the divalent cations of the alkaline earth metals. It is proposed that not only in the R-band formation with the hydroxides of the alkaline earth metals but also in that obtained by other techniques, chromosome stabilization plays an important role.