Lethal genes in O-5 chromosomes of Drosophila subobscura from Europe and America

In populations of D. subobscura. a species that is know for its high chromo somal polymorphism, the O-5 inversion has a rather erratic frequency distri bution in the Palearctic region. An O-5 lethal chromosomal line obtained fr om a Balkan population near Zanjic (South Adriatic, Montenegro, Yugoslavia) was tested for lethal allelism with other O-5 lethal chromosomal lines der ived from American (USA and Chile) colonizing populations. and from the Fre nch population of Taule, No allelism was found between the Balkan lethal ge ne and those from America and France. Thus, the lethal genes of the O-5 inv ersions are not of the same origin and it is most probable that the America n colonizations did not start from the Zanjic population The general differ ence in the chromosomal inversion polymorphism corroborates this conclusion . The cytological analysis confirms the assumption that all O-5 chromosomes studied are identical with respect to breakage points.