The effect of inversions on mitotic recombination in Drosophila melanogaster

The effect of inversions on mitotic recombination outside the inversion was studied in inversion-heterozygotes. Seven euchromatic inversions of the X-chromosome, with breakpoints within the interval between two cell markers, were chosen. The size of the inverted region and the distance from the proximal breakpoint to the proximal cell marker varied. Mitotic recombination was X-ray induced in larvae and clones scored in the tergites of emerged adults. The frequency of recombinants between both cell markers and the frequency of recombinants proximal to the proximal cell marker was used to estimate the effect of interference in pairing caused by the inversions. Such an effect only occurs in small chromosome intervals. This indicates that homologous sequences are tightly paired in the interphase nuclei of somatic cells. This conclusion is derived from data based on X-ray induced mitotic recombination. The possibility of extending this conclusion to non-irradiated cells is discussed.