Some Aspects on the Variability of the Satellitized Arm, in Human Acrocentric Chromosomes

Abstract

The five pairs of acrocentric chromosomes in the human complement (groups D and C) have a heterochromatic zone or secondary constriction between the cen tromere and the distal part of the shorter arm, which Ohno et al. (1961) characterized as the region where the nucleolus is organized. Fergusson-Smith and Handmaker (1961) drew attention to the presence of satellites in all of them. The nucleolar organizer is a region which is hyperactive in RNA synthesis (Jain et al. 1969) and it is here that the synthesis of ribosomal RNA takes place (Ritossa and Spiegelman 1965, Brinstiel et al. 1966).