[Variability of the heterochromatic regions of human chromosomes 1, 9, 16, and Y].

The variability of heterochromatic regions on chromosomes 1, 9, 16 and Y has been studied in a group of unrelated subjects (50 boys and 50 girls) using quantitative methods. Analysis of intercellular (with one subject) variability of chromosome C-segments lengths has shown that their absolute lengths vary considerably with the cell sample examined, while the relative lengths (a part of the total length of C-segment of the chromosomes being studied) are more stable. The relative lengths may be helpful in individual characteristics, reproducible in repeated analysis, which may be used in zygosity testing in twins, family analysis, etc. Absolute lengths, however, may be successfully used in population studies, as the difference between the cell samples peculiarities on which the C-segment length is based in particular karyotypes, is obliterated. Comparative analysis of mean lengths and variability of C-segments on chromosomes 1, 9, 16 in the groups of boys and girls has revealed no differences between the sexes. The mean lengths and the standard deviations of C-segments' lengths on chromosomes 1, 9, 16 and Y obtained in this study are 1.26 +/- 0.23; 1.13 +/- 0.20; 0.85 +/- 0.14; 1.13 +/- 0.21 mcm respectively. Identical data on both sexes, as well as the normal distribution of C-segments' lengths confirm the idea that the length of the C-segment is a neutral characteristic in normal population.