Regulation of ribosomal RNA gene multiplicity in Drosophila melanogaster.

The ribosomal RNA (rRNA) genes of Drosophila melanogaster can undergo a disproportionate replication of their number. This occurs when the cluster of rRNA genes (rDNA) of one chromosome is maintained with a homologous chromosome that is completely or partially deficient in its rDNA. Under appropriate genetic conditions, it appears that disproportionate rDNA replication can be generated at the level of both somatic and germ line cells. In the latter case, mutants partially deficient for rDNA can increase their rRNA gene number to the wild type level and transmit this new genotype to successive generations.