The frequency and staining intensity of the dark bands were measured in 6985 trypsin G-banded human chromosomes, described by so-called band transition sequences which represent the chromosome banding patterns in a condensed quantitative way. In the haploid chromosome complement a maximum of 351 bands were registered: 181 white and 170 dark bands. The frequency with which bands occurred and the staining intensity of the bands differed considerably between the chromosome types. Among the dark bands the darker stained bands occurred more frequently than the lighter stained bands. A study of the relationship between the degree of chromosome contraction and the frequency of band occurrence revealed that for all chromosome types the average band frequency increased with increasing chromosome elongation. Twenty of the 23 dark bands chosen as landmarks by the Paris Conference (1971) occurred with high frequency and staining intensity. The remaining three landmarks occurred less frequently, due to fusion of dark and white bands, respectively.
A study of global features showed, as expected, good agreement between chromosome length, area and density. There was good agreement between the centromeric indices determined by length and area, respectively, and no difference was found between contracted and elongated chromosomes, with the exception of the acrocentrics where elongated chromosomes showed higher centromeric indices than contracted chromosomes. Most often, the centromeric index by density differed considerably from the centromeric indices by length and area, respectively.
The data presented here may be used in clinical cytogenetics as a supplement to the ISCN idiograms (ISCN 1978), as the band frequencies and staining intensities may help in identifying and characterizing specific bands.