COMPUTER-ORIENTED ANALYSIS OF HUMAN CHROMOSOMES IV. DEOXYRIBONUCLEIC ACID-BASED CENTROMERIC INDEX

Abstract

A density-oriented semiautomatic method to estimate centromeric index is described and tested on 4611 human chromosomal images. Chromosomes are stained for deoxyribonucleic acid with gallocyanin-chrome alum and their optical density is recorded by a digital scanning microscope. Shape information in the chromosome boundary leads to a provisional centromeric position. The chromosome is divided into strips 0.25-0.35 µm wide paralleling the centromere. Optical density is integrated within each strip, strips are assembled into a density profile and the definitive centromere is located at the major local minimum in the profile. Centromeric index (large arm:total) is based on optical density or area. A test set of 4611 chromosomal images is based on over 2500 chromosomes (56 metaphase cells from six individuals) and excludes overlapped and excessively bent chromosomes. The program fails in 1.2% of the test images. Standard deviation within chromosome groups of centromeric index based on density is 0.024 and replication error is 0.016. Systematic differences between area-based and density-based measurements are observed and interpreted.