Similarities and differences in the structure of X and Y chromosome rRNA genes of Drosophila

Abstract

In D. melanogaster, the rRNA genes (rDNA) are clustered at single sites on 2 non-homologous chromosomes, the X and Y. Examination of the structure of X and Y rDNA with restriction endonucleases [EcoRI from Escherichia coli and SmaI from Serratia marcescens] reveals that the X rDNA contains repeating units not present in the Y. Such observations, as well as genetic evidence, illustrate difficulties with the hypothesis that recombination is the predominant mechanism preserving similarities between these 2 clusters maintained on different chromosomes. This raises the possibility that selection pressure has a significant role in maintaining the parallel evolution of these 2 separate but homologous redundant gene clusters.