DNA cytophotometry of human chromosomes

Abstract

The applicability of Feulgen-based parameters to detect variant metaphase chromosomes involved in deletions or translocations, was investigated and algorithms developed to compute such parameters. This report is focused primarily on the magnitude of the errors involved during the prerequisite procedures of photography, measurement and computation. Measurements were performed by stage-scanning of photographic negatives of Feulgen-stained metaphases. In the scanned images the initial chromosome boundaries were obtained by thresholding, while definite chromosomal areas and local background values were obtained by expansion of the initial boundaries. The integrated density profiles and the relative DNA content were computed for the individual chromosomes (straight as well as bent). Total DNA content, DNA arm ratio, as well as length and centromere index can be obtained from the profile. It was shown that under such conditions the experimental errors associated with the measurements are small compared to biologic variations (e.g., differences between homologues) and that the procedures applied allow to detect polymorphisms. In addition to this, mean and standard deviations of both DNA and length parameters are given for metaphases of five subjects. Comparison of the applicability of DNA and length parameters is realized by a classification experiment.