Heterochromatic position effect at the rosy locus of Drosophila melanogaster: cytological, genetic and biochemical characterization.

This report describes cytological, genetic and biochemical studies designed to characterize two gamma-radiation induced, apparent "underproducer" variants of the rosy locus (ry:3-52.0), ryps1149 and ryps11136. The following observations provide a compelling basis for their diagnosis as heterochromatic position effect variants. They are associated with rearrangements that place heterochromatin adjacent to the rosy region of chromosome 3 (87D). The effect of these mutations on rosy locus expression is subject to modification by abnormal Y chromosome content. The rearrangement alters only the expression of the rosy allele on the same chromosome (cis-acting). The Y chromosome modification is only on the position-affected allele's expression. The recessive lethality associated with the rearrangements relate to specific rosy region vital loci, and for ryps11136, the lethality is not Y chromosome modified. The peptide product of the position-affected allele is qualitatively normal by several criteria. Heterozygous deletion of 87E2-F2 is a suppressor of the rosy position effect. The rosy position effect on XDH production may be assayed in whole larvae and larval fat body tissue as well as in adults.