DIFFERENTIATION OF MULLERS CHROMOSOMAL ELEMENT-D AND ELEMENT-E IN THEOBSCURA GROUP OF DROSOPHILA

Twenty-two markers located on Muller's elements D or E have been mappe d by in situ hybridization in six species of the obscura group of Dros ophila and in D. melanogaster. The obscura species can be grouped into a Palearctic cluster (D. subobscura, D. madeirensis and D. guanche) a nd a Nearctic one (D. pseudoobscura, D. persimilis and D. miranda). El even of the probes contain known genes: E74, Acp70A, Est-5, hsp28/23 h sp83, 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 chrom osomal arm of elements D and E. Thus, these elements have conserved th eir genic content during species divergence. Chromosomal homologies pr oposed previously for each element among the species of the same clust er have been compared with the present results. The distribution of ma rkers within each element has changed considerably as inferred from pa irwise comparisons of obscura species included in the two different cl usters. Only chromosomal segments defined by closely linked markers ha ve been conserved: one such segment has been detected in element D and three in element E between D. subobscura and D. pseudoobscura.