Computer image analysis of variance between human chromosome replication sequences and G-bands.

A computer image analysis system was applied to the quantitative study of chromosomal early- and late-replication patterns from the leukocytes of several normal human donors, and these patterns were compared with the chromosomal G-banding patterns. The first and last few hours of replication were discriminated by selective bromodeoxyuridine vs. thymidine incorporation in DNA and a Hoechst-blacklight-Giemsa stain technique. Image analysis with Tufts Piquant system involved automatic determination of chromosome boundaries, centromeres and telomeres, linear chromatid axes, chromatid density measurements along each axis, and comparative length normalized density profiles for each chromatid and the chromosome. Consistent complementary early- and late-replication patterns were determined for autosomes 1-6 and the X chromosomes. Limited intracellular or interindividual variability occurred in the intensity of a few active replication peaks but not in their location. However, there were very distinct regions of noncorrespondence between the late-replication patterns and the G-band patterns, in contrast with previous observations, although many similarities were also evident. These differences are interpreted with reference to a general model of replication sequence control of cell differentiation.