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

Scott M. Williams 1, Glenn R. Furnier 2, Eric Fuog 1, and Curtis Strobeck 1

1 Department of Zoology, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
2 Department of Forest Science, University of Alberta, Edmonton, Alberta T6G 2E9, Canada

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.

Submitted on June 23, 1986
Accepted on February 27, 1987