Human chromosomal heteromorphisms in Delhi newborns. IV. Inter-relationship between C-band size and inversion heteromorphisms.

The inter-relationship of C-band size and inversion heteromorphisms was studied in 200 Delhi normal newborns (100 males and 100 females). A significant correlation between size and inversion heteromorphisms in males (r = 0.97) and females (r = 0.98) was observed. The results suggested that the larger the size of the C-band regions so the higher was the incidence of inversion.

A comparison of constitutive heterochromatin staining methods in two cases of familial heterochromatin deficiencies.

Using DAPI staining after pretreatment with distamycin A we detected a familial deficiency of chromosome 16 heterochromatin. A distinct positively staining band, however, was seen after C-banding. Thus, by using these different heterochromatin staining methods, heterogeneity of the constitutive heterochromatin in the centromeric region of human chromosome 16 was indicated. The same C-banding procedure was also applied to a previously described familial deficiency of chromosome 9 heterochromatin evidenced using distamycin A/DAPI staining and G 11 staining (Buys et al., 1979). In this case a C-band appeared to be virtually absent on the relevant chromosome. These staining methods may be valuable tools in the study of chromosome polymorphisms.

DNA content and DNA-based centromeric index of the 24 human chromosomes.

The chromosomes of two human males were identified by fluorescent banding, restained, and measured by scanning microscopy and computer analysis. The two variables, DNA content and DNA-based centromeric index, provided almost complete discrimination of chromosome types. Some chromosomes showed significant differences in DNA content between the men, and for one man two pairs of chromosomes showed significant differences between homologs.

Compositional heterogeneity of human heterochromatin.

When human genome was fractionated by thermal elution chromatography, repetitious DNA was found in every arbitrary temperature segment. When these repetitious DNA families were used for in situ hybridization, the following conclusions were evident: (a) Unlike the case of mouse, where essentially all centromeric heterochromatins appear to be composed of one DNA family, human heterochromatin is composed of various DNA families. (b) Some human heterochromatin pieces, (e.g., that of chromosome 9) appear to have more heterogeneous composition than others (e.g., that of chromosome 1). (c) The highly repetitious human DNA fractions are located primarily at the centromeric and telomeric regions, but the interstitial regions also contain these fractions. (d) The more slowly reassociating repetitious sequences are distributed over the length of the chromatid, with a slight bias in favor of the telomeric regions. (e) The repetitious DNA fractions of higher (guanine + cytosine) content have less affinity for the centromeric regions.