| PubMed Abstract |
Nine single copy regions located on the X chromosome have been mapped by in situ hybridization in six species of the obscura
group of Drosophila. Three Palearctic species, D. subobscura, D. madeirensis and D. guanche, and three Nearctic species, D.
pseudoobscura, D. persimilis and D. miranda, have been studied. Eight of the regions include known genes from D. melanogaster
(Pgd, zeste, white, cut, vermilion, RNA polymerase II 215, forked and suppressor of forked) and the ninth region (lambda DsubF6)
has not yet been characterized. In all six species, as in D. melanogaster, all probes hybridize to a single site. Established
chromosomal arm homologies of Muller's element A are only partly supported by present results since two of the probes (Pgd
and zeste) hybridize at the proximal end of the XR chromosomal arm in the three Nearctic species. In addition to the centric
fusion of Muller's A (= XL) and D (= XR) elements, the metacentric X chromosome of the Nearctic species requires a pericentric
inversion to account for this result. Previously proposed homologies of particular chromosomal regions of the A (= X) chromosome
in the three species of the D. subobscura cluster and of the XL chromosomal arm in the three species of the D. pseudoobscura
cluster are discussed in light of the present results. Location of the studied markers has changed drastically not only since
the divergence between the melanogaster and obscura groups but also since the Palearctic and Nearctic species of the obscura
group diverged.
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