Human Q and C chromosomal variations: distribution and incidence.

Chromosome preparations of 77 normal newborn babies from Grand Junction, Colorado, were stained first for G-band identification of each chromosome and subsequently stained for Q- and C-band localization. This approach permitted determination of the variation of the C region size in all chromosomes, and is the first such study reported. A total of 391 Q and C variants was described, an average of 5.08 +/- 0.23 per subject; 225 were Q varients, 166 were C variants. Q varients were distributed among seven chromosomes in the genome and among 76 of the 77 subjects. Chromosomes 3 and 4 had variable Q intensities at the centromere, and the acrocentric chromosomes, 13, 14, 15, 21, and 22, had variable Q intensities in their short arms and/or satellites. C variants, though fewer in number, were more widely distributed in the genome, with at least one variant described in each chromosome. C variants were identified in 65 of the 77 subjects. Most unique were the six pericentric inversions found in chromosome 9. Except for giant satellites, no correlations were found between Q and C variants. Q and C variants evaluated in 16 members of four families showed that in nearly every case each variant observed in a child could be demonstrated in one or both parents. It is evident from this study that the magnitude of chromosomal variation in human populations is far greater than heretofore believed. It has also been shown that the combination of Q- and C-banding procedures will yield much more information than either technique used alone and is therefore the preferred approach to many population and gene localization studies.