Evolution of 5S ribosomal RNA genes in the chromosomes of the virilis group of Drosophila.

Drosophila melanogaster 5S ribosomal RNA labeled with 125I was used as an in situ hybridization probe to localize complementary sequences in chromosomes of species in the Drosophila virilis group. Whereas virilis, the ancestral species, has two different 5S gene loci, the derived species show only one of these loci; in the two lines that have evolved from virilis it is the opposite locus that is conserved. The possible events leading to such an arrangement are discussed.