Nucleolar dominance in diploid and triploid parthogenetic lizards of hybrid origin

Abstract

Silver staining of nucleolus organizer regions (NORs) in diploid cells of bisexual species of whiptail lizards (<i>Cnemidophorus</i>) indicated codominance of the rRNA genes on homologous chromosomes, However, a nucleolar dominance hierarchy was revealed by inactivity of specific NORs in diploid and triploid cells from natural unisexual clones of hybrid origin. Often, only one NOR was active in cells of these diploid or triploid parthenogenetic species, and activity depended on the dominance hierarchy, not maternal inheritance or dosage compensation. This is in striking contrast to the gene activity previously observed in the same lizards but based on the electrophoretic analysis of other gene products, in which there was codominance of all alleles at each locus studied in triploid and tetraploid lizards. These results indicate that ribosomes produced by the dominant rRNA gene of one ancestor in hybrid cells function adequately in synthesizing polypeptides encoded by other codominant genes from two or three ancestors.