Structural organization of the heterochromatic region of human chromosome 9.

Giemsa-11, G-banding and Lateral Asymmetry staining techniques were used to define the substructure of the C-band heterochromatin of human chromosome 9, in a sample of 108 different chromosomes 9, from 54 individuals. In this sample, the juxtacentromeric portion of the C-band region stained positive by the G-banding technique while Giemsa-11 delineated a more distally located block. Examination of the pericentric inversions generally revealed that the entire C-band region is changed with the substructural organization left intact; i.e. the G-band is proximal, the G-11 distal to the centromere. The "partial pericentric inversions" were found to have larger than average amounts of G-band heterochromatin on the short arm. The G-11 staining was in its usual position on the long arm with none on the short arm. Such apparent inversions therefore may not represent true inversions. Long heterochromatic regions frequently had a segmented appearance when stained with G-11; there was a dark G-band within the pale heterochromatic region when stained with the G-banding technique which corresponded in location to the achromatic gap produced by G-11. This extra G-band may have been derived from the juxtacentromeric G-band by processes analogous to unequal crossing over. Simple lateral asymmetry was consistently present only in the G-band heterochromatin of those chromosomes 9 containing large blocks of G-band positive material. Examination of the portion of the C-band which would correspond to the G-11 positive material revealed no consistent patterns of asymmetry. Usually both strands were heavily stained and symmetrical but occasionally there were light areas present on one strand suggestive of compound lateral asymmetry.