Conservatism of sites of tRNA loci among the linkage groups of severalDrosophila species

The sites of seven tRNA genes (Arg-2, Lys-2, Ser-2b, Ser-7, Thr-3, Thr-4, Val-3b) were studied by in situ hybridization.125I-labeled tRNA probes fromDrosophila melanogaster were hybridized to spreads of polytene chromosomes prepared from fourDrosophila species representing different evolutionary lineages (D. melanogaster, Drosophila hydei, Drosophila pseudoobscura, andDrosophila virilis). Most tRNA loci occurred on homologous chromosomal elements of all four species. In some cases the number of hybridization sites within an element varied and sites on nonhomologous elements were found. It was observed that both tRNA 2 Arg and tRNA 2 Lys hybridized to the same site on homologous elements in several species. These data suggest a limited amount of exchange among different linkage groups during the evolution ofDrosophila species.