Concomitant 'C' and 'G' bands in human chromosomes

Constitutive heterochromatin in mammalian chromosomes was first demonstrated in 1970 by hybridization of radio labeled DNA with the DNA of cytological preparations. The technique has been modified subsequently to reveal either 'C' or 'G' bands; thus far, however, 'C' banding techniques do not satisfactorily identify 'G' bands, and vice versa. The authors developed a technique utilizing sequential 0.1 M NaOH and 0.05% trypsin treatments, which consistently reveals both 'C' and 'G' bands in the same preparation and which shows a clearer delineation of the 'C' bands than is usually seen by the standard 'C' band methods. Thus they observed consistent differentiation of the 'C' band of the #1 chromosome into three distinct bands, frequent similar differentiation of the 'C' band of the #9 chromosome and differentiation of the Yq12 band into at least two bands. Investigation of a patient with 46,XX, inv(12) (p13q11) by this technique indicates that the functional centromere does not occupy the whole of the #12 'C' band. A similar phenomenon probably accounts for the 'inactivated centromere' observed with some translocations. The technique is suggested as the method of choice for 'C' banding studies.