The effect of eye reduction on White position-effect variegation in Drosophila melanogaster

Abstract

Position-effect variegation for the white locus was studied in normally shaped eyes and in reduced eyes of Bar (B) and Drop (Dr) flies. The average number of spots per eye is successively lower in +, B, and Dr eyes; moreover, B eyes show a relatively strong pigmentation. No simple relation seems to be present between the degree of pigmentation and the number of facets, either between +, B, and Dr eyes or within classes of Dr eyes that have been analysed.The chance that ommatidia will become pigmented follows a gradient across mottled eyes of wild-type shape that seems fixed early in development. The gradient is less clear or absent in B eyes.The results are best interpreted on the basis of the cell-lineage theory and an early one-sided action of B on the developing eye disc after fixation of the gradient.

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

“…Our cursory observations on wm 158-21 (unpublished) also showed pigment preferentially located in the ventro-posterior region. A more detailed investigation of T( 1; 4) mKrist in D. hydei (van Breugel, 1972) revealed an anterior-posterior gradient and a less marked oblique dorsoventral gradient, pigment being preferentially located in the upper posterior part of the eye. In wm4 the pigment appears to be distributed in a very different manner: the unpigmented ommatidia are concentrated towards the middle of the eye in all groups, and their frequency decreases towards the rim.…”

“…The size of the patches reflects the developmental stage at which this event occurs (Becker, 1978). A common characteristic of white-variegated eyes is a tendency for the affected, usually unpigmented, ommatidia to decrease in frequency towards the posterior edge of the eye, resulting in a roughly anterior-posterior pigmentation gradient (e.g., van Breugel, 1972).…”

Euchromatic inversions causing mosaic gene expression in Drosophila hydei: A study of forked and Zebra

“…This resembles the pigmentation gradient in variegated white eyes showing the highest chance of pigment formation at the posterior rim of the eye [Van Breugel, 1972, 19731. It seemed interesting to find out how the two types of bristles (f and f+) are patterned in the forked mosaics. Is a mechanism of clonal expression present based on an early timing of gene switch and subsequent transfer of the decision to daughter cells [see Becker, 1961Becker, , 1966 or does a pepper-and-salt type of variegation Breugel, 1972Breugel, , 1973? If two neighbouring bristles of the normal pattern often show the same phenotype this would support a field or patchlike type of determination.…”