Modification of gene suppression in Drosophila melanogaster by sex chromosomes: II. Variegation in eyes of wm4 males

Abstract

SUMMARYWe studied position-effect variegation in left eyes of w"4 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.

Live analysis of position-effect variegation in Drosophila reveals different modes of action for HP1a and Su(var)3-9

“…In the variegation of the SwiM system GAL80 allele, we could detect no such reproducibility, nor could we detect any influence by unlinked modifiers of variegation in our strains ( 11 ). The difference between their observations and the behaviors of the GAL80 locus we use here is not immediately clear; however, it may be that they selected for expression in regions of the eye that poorly repress variegating gene expression ( 18 ) or for modifiers that have preferential effects at certain loci ( 19 ).…”

Modification of gene suppression in Drosophila melanogaster by sex chromosomes 3. Heterochromatisation associated with the wm4 phenotype

“…An alternative, albeit less direct, approach is to analyse the phenotype of affected organs and heterochromatisation in the same strain. We recently obtained quantitative information on white-variegation in Malpighian tubules and eyes of males carrying In(1)wm4 (Hartmann-Goldstein and Koliantz, 1981;Koliantz et a!., 1984). The present paper deals with observations on the salivary gland chromosomes of wm4/yY, wm4,/y and wm4/O larvae in relation to some of the questions arising from phenotypic studies.…”