The Amplified Ribosomal DNA of Dytiscid Beetles

Abstract
During oogenesis in many animals there is a massive extrachromosomal synthesis of the genes for ribosomal RNA. In Dytiscid beetles, as in the toad Xenopus , the amplified ribosomal DNA occurs as circular molecules of different sizes. The circles fall into size classes that are integral multiples of a unit circle. It is probable that the unit circle contains the coding sequence for one precursor ribosomal RNA molecule plus accompanying spacer sequences.