Differentiation of Muller's chromosomal elements D and E in the obscura group of Drosophila.

Twenty-two markers located on Muller's elements D or E have been mapped by in situ hybridization in six species of the obscura group of Drosophila and in D. melanogaster. The obscura species can be grouped into a Palearctic cluster (D. subobscura, D. madeirensis and D. guanche) and a Nearctic one (D. pseudoobscura, D. persimilis and D. miranda). Eleven of the probes contain known genes: E74, Acp70A, Est5, hsp28/23, hsp83, emc, hsp70, Xdh, Acph-1, Cec and rp49. The remaining probes are recombinant phages isolated from a D. subobscura genomic library. All these markers hybridize to the putative homologous chromosome or chromosomal arm of elements D and E. Thus, these elements have conserved their genic content during species divergence. Chromosomal homologies proposed previously for each element among the species of the same cluster have been compared with the present results. The distribution of markers within each element has changed considerably as inferred from pairwise comparisons of obscura species included in the two different clusters. Only chromosomal segments defined by closely linked markers have been conserved: one such segment has been detected in element D and three in element E between D subobscura and D. pseudoobscura.