Lack of intercellular suppression of position-effect variegation by supernumerary Y chromosomes during cell differentiation in Drosophila melanogaster.

The objective of this research was to determine whether there is intercellular suppression of position-effect variegation by extra-heterochromatin during cell differentiation (pupation) in Drosophila melanogaster. The results provide some indication as to the mechanism and timing for the general suppression of position-effect variegation by supernumerary heterochromatin in the genome. Imaginal discs were excised from larvae having the necessary chromosomal rearrangement required for position-effect variegation and were transplanted into larvae with and without additional Y chromosomes in their genomes. After metamorphosis, the explants were examined to determine the effect of their respective hosts. There were no differences in the extent of variegation between eyes transplanted into hosts carrying different amounts of extra-heterochromatin. Thus, extra-heterochromatin position-effect variegation does not suppress during cell differentiation or, if it does, the action is intracellular.