Partial reversion at the bobbed locus of Drosophila melanogaster

In Drosophila melanogaster the tandemly arranged repetitive sequences coding for 18S and 28S rRNA are heterogenous at the level of the spacers between units and insertions that interrupt many 28S rRNA genes. This heterogeneity contrasts with the homogeneity of the regions transcribed into 18S and 28S rRNA. Homogenization and evolution of repetitive genes are usually explained by conversion, amplification events or unequal crossovers. In this paper we studied the change in rDNA patterns associated with partial reversion of bobbed mutations. In most cases, no increase in rDNA gene number, but a new repartition of gene types were found.