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- Studies of the species barrier between Drosophila subobscura and D. madeirensis. III. How universal are the rules of speciation?Publication . Khadem, Mahnaz; Krimbas, Costas B.The prevalence of Haldane's rule and the large effect of the X chromosome are examined by analysing the genetics of seven abnormal characters in interspecies hybrids between D. subobscura and D. madeirensis. In two cases Haldane's rule is not obeyed (viability and abnormality of the head). In all characters except the abnormal abdominal tergites, an important effect of the X chromosome is observed. There is an asymmetry in the importance of the effect of the X chromosome. The X of D. madeirensis origin induces abnormality mostly in a mixed background. TheY chromosome plays an important role in determining male sterility.
- Studies of the species barrier between Drosophila madeirensis and Drosophila subobscura. II. Genetic analysis of developmental incompatibilities in hybridsPublication . Khadem, Mahnaz; Krimbas, Costas B.The genetic analysis of two abnormal Characters, extra sex combs and abnormal head shape in hybrids between Drosophila madeirensis and Drosophila subobscura, revealed a major effect of the X chromosome in both cases. Autosomes also play a role in determining these abnormalities, the E chromosome in case of extra sex combs, the E and 0 chromosomes in case of abnormal head shape. Autosomes do not cause the two abnormal characters, without interacting with the X chromosome.
- Studies of the species barrier between Drosophila subobscura and D. madeirensis I. The genetics of male hybrid sterilityPublication . Khadem, Mahnaz; Krimbas, Costas B.The genetics of hybrid male sterility between Drosophila subobscura and D. madeirensis were studied with the help of 20 markers in backcross males. A major effect resides in the sex chromo somes: backcross males with the X and Y of different origin (mad X-sub Y or sub X—mad Y) have very small and empty testes. In compatible combinations testes are of normal size but males may be sterile or fertile depending on the genetic constitution of their autosomes. Six autosomal factors affecting hybrid male fertility could be postulated. This estimation is based on the assumption of the absence of interaction between viability and fertility. The presence and the mode of such interaction may modify the number of sterility factors.