Gene action in fish of tetraploid origin. III. Ribosomal DNA amount in cyprinid fish.

Phylogenetically diploid and tetraploid cyprinid fish species have cells of very similar volumes and protein contents. This finding has prompted us to postulate a regulatory system established during the evolution of the tetraploids leading to a diploid state of genic expression. It was proposed that this might be accounted for by a selective loss of ribosomal genes. RNA-DNA hybridization experiments, however, reveal a clear-cut 1:2 relationship of ribosomal DNA amounts between the diploid and the tetraploid species.