STUDIES OF THE SPECIES BARRIER BETWEEN DROSOPHILA-SUBOBSCURA AND D-MADEIRENSIS .3. HOW UNIVERSAL ARE THE RULES OF SPECIATION

The prevalence of Haldane's rule and the large effect of the X chromos ome are examined by analysing the genetics of seven abnormal character s 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, a n important effect of the X chromosome is observed. There is an asymme try in the importance of the effect of the X chromosome. The X of D. m adeirensis origin induces abnormality mostly in a mixed background. Th e Y chromosome plays an important role in determining male sterility.