The volumes and morphology of human chromosomes in mitotic reconstructions

Ten unpretreated normal human male fibroblast cells in mitosis were completely reconstructed from micrographs of between 82 and 119 consecutive serial sections. All 46 chromosomes and their centromeres could be reconstructed in every cell. Measurements of chromosome volumes and centromere indices are presented. The data enabled allocation of all chromosomes to their groups (A to G), and chromosomes 1, 2, 3, 6, 9, 16, 17, 18 and Y were individually identified. Comparisons with published karyotypes showed that volume measurements correlated well with measurements of DNA content and chromosome length. Centromere indices also showed good correlation, but the acrocentric chromosomes were more unequally armed than found by length measurement. Secondary constrictions at the nucleolar organising region were visible on about a third of the acrocentric chromosomes. One chromosome of the C group, number 9, had a diffuse subcentromeric region (DSR) on the long arm, at the position of the constitutive heterochromatin and (in meiotic cells) the paramere.