Modification of gene suppression in Drosophila melanogaster by sex chromosomes: II. Variegation in eyes of w^m4 males

Summary

We studied position-effect variegation in left eyes of w^m4 males with none, one or two Y chromosomes, reared at 25°C or 15°C. The results showed that an additional Y chromosome reduces both the number of variegated flies and the mean number of affected ommatidia, whereas loss of the Y chromosome markedly enhances both. Low culture temperature also enhances the variegation but is less effective than loss of the Y chromosome. Comparisons of variegation patterns between the different experimental groups were hampered by considerable variation between individuals within a group. “Average” patterns were therefore constructed for each group, which are presented in the form of computer-smoothed contour maps and three-dimensional perspectives. They revealed that the distribution of pigment differs in various respects from that observed in other white-variegated strains. Notably, the highest concentration of unpigmented ommatidia occurs in the middle of the eye, decreasing more or less radially though not all peripheral regions are equally affected. Pattern differences associated with differences in Y-chromosome constitution are ascribed to a combination of the factors which determine regions of sensitivity and those which enhance variegation.