Reduced DNA polytenization of a minichromosome region undergoing position-effect variegation in Drosophila

Cell. 1990 Oct 5;63(1):97-107. doi: 10.1016/0092-8674(90)90291-l.


Molecular analysis of a Drosophila minichromosome, Dp(1;f)1187, revealed a relationship between position-effect variegation and the copy number reductions of heterochromatic sequences that occur in polytene cells. Heterochromatin adjacent to a defined junction with euchromatin underpolytenized at least 60-fold. Lesser reductions were observed in euchromatic sequences up to 103 kb from the breakpoint. The copy number changes behaved in all respects like the expression of yellow, a gene located within the affected region. Both copy number and yellow expression displayed a cell-by-cell mosaic pattern of reduction, and adding a Y chromosome, a known suppressor of variegation, increased both substantially. We discuss the possibility that changes in replication alter copy number locally and also propose an alternative model of position-effect variegation based on the somatic elimination of heterochromatic sequences.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Chromosome Deletion
  • Chromosome Mapping*
  • DNA / genetics*
  • Drosophila / anatomy & histology
  • Drosophila / genetics*
  • Female
  • Heterochromatin / physiology
  • Heterochromatin / ultrastructure
  • Male
  • Mutation
  • Nucleic Acid Hybridization
  • Restriction Mapping
  • Salivary Glands / physiology


  • Heterochromatin
  • DNA