, Volume 94, Issue 6, pp 492–504 | Cite as

Cytogenetic and molecular aspects of position effect variegation in Drosophila melanogaster

I. Morphology and genetic activity of the 2AB region in chromosome rearrangement T(1;2)dorvar7
  • I. F. Zhimulev
  • E. S. Belyaeva
  • O. V. Fomina
  • M. O. Protopopov
  • V. N. Bolshakov


A new genetic model system for studying position effect variegation in Drosophila melanogaster was found. It allows the analysis of genetic inactivation and changes in chromosome morphology in the same cells. In T(1;2)dorvar7 strains the 2B5 early ecdysone puff, and the ecs locus which maps in this puff are translocated into the vicinity of centromeric heterochromatin. The ecs locus plays a key role in the system of ecdysone puffs: genetic damage to this locus results in loss of sensitivity of cells to the hormone and, as a consequence, ecdysone-induced puffs do not develop. In the T(1;2)dorvar7 chromosome the ecs and at least five adjoining loci are inactivated in a variegated fashion. In the salivary gland cells of T(1;2)dorvar7/ ecslt435 0 h prepupae which do not show the ecdysone puffs, the morphology of the 2B region was analysed. In all cases where the ecs locus was inactivated, a dense block of chromatin reminiscent of a solid band was found in the 2B region instead of the four bands 2B1–2, 3–4, 5 and 6. Sometimes compaction of the chromatin reached the 2A1–2 or even 1E1–4 bands. Formation of the compact block of chromatin coincided with late replication in this region. In situ hybridization of polytene chromosomes with a DNA clone from the ecs locus showed that when the dense chromatin block was present, no DNA was accessible for hybridization in 2B5. Hybridization of DNA of another clone located in the region of the translocation breakpoint (2B7–8) was found only in polytene chromosomes of larvae grown at 25° C, and never in those grown at 18° C, independently of the morphology of the 2B5 puff. The possibility that in the case of block formation both late replication and, as a consequence, underreplication of chromosome DNA take place, is discussed.


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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • I. F. Zhimulev
    • 1
  • E. S. Belyaeva
    • 1
  • O. V. Fomina
    • 1
  • M. O. Protopopov
    • 1
  • V. N. Bolshakov
    • 1
  1. 1.Department of Molecular CytogeneticsInstitute of Cytology and GeneticsNovosibirskUSSR

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