Abstract
A Tunisian natural population of Drosophila melanogaster has been screened for chromosome inversion polymorphism. All 10 of the inversion types found are paracentric and autosomal. Five of these are cosmopolitan: common, In (2L)t and In(2R)NS, or rare, In (2R)Cy, In (3R)C and In(3R)M. The others are new endemic, with the exception of In(2L)Cy. This inversion, the break points of which are very close, both distally and proximally, to those of In(2L)t, was never formally described in a natural population before and seemed to be only a laboratory stock rearrangement. The presence of In(2L)Cy has been established unequivocally by crossing males from the Tunisian lines with virgin females from a (2L)Cy-type strain. From the results, In(2L)Cy appears to exist in at least one natural population. It is possible that this chromosome sequence might occur in another population, but described as In(2L)t because of the close similarity of these two inversions.
