STUDIES OF THE SPECIES BARRIER BETWEEN DROSOPHILA-SUBOBSCURA AND DROSOPHILA-MADEIRENSIS IV - A GENETIC DISSECTION OF THE X-CHROMOSOME FOR SPECIATION GENES

The genetics of foul-traits contributing to the isolation mechanism be tween the two closely related species of Drosophila belonging to the o bscura group, L. subobscura and D. madeirensis, have been investigated , especially regarding the influence exerted by the X chromosome. This chromosome has been roughly dissected genetically by the use of four markers. It was found that factors affecting viability of backcross ma les are spread from the centromeric end of the chromosome up the regio n marked by Bx. Three sections were responsible for male sterility/fer tility. The abnormal head shape of the backcross males was affected by factor(s) on the madeirensis and the subobscura sex chromosome locate d at the region of MAD1 inversion. Finally, an abnormal trait in these males (presence of extra sex combs) was found to be controlled by fou r sections, two on the madeirensis X chromosome and two on the subobsc ura one.