Evolution of the Ribosomal DNA Spacers of Drosophila melanogaster: Different Patterns of Variation on X and Y Chromosomes

摘要

Length variation of the ribosomal gene spacers of Drosophila melanogaster was studied. Analysis of 47 X chromosomal and 47 Y chromosomal linked rDNA arrays collected from five continents indicates that the arrays on the two chromosomes differ qualitatively. The Y -linked arrays from around the world share little or no similarity for either their overall length or the organization of their spacers. Most of the X -linked arrays do, however, share a major length spacer of 5.1 kb. In addition, those X -linked arrays that have a major 5.1-kb band have similar spacer organization as demonstrated by genomic DNA digestions with several restriction enzymes. These data strongly support the hypothesis that spacer length patterns on only X -linked genes are maintained primarily by natural selection.