, Volume 102, Issue 1, pp 15–19 | Cite as

Replication forks are not found in a Drosophila minichromosome demonstrating a gradient of polytenization

  • Robert L. Glaser
  • Gary H. Karpen
  • Allan C. Spradling
Original Articles


Differential DNA replication is widely held to influence polytene chromosome structure by causing the dramatic reductions in heterochromatic DNA content that are characteristic of most endopolyploid cells. The “underreplication model” of heterochromatic sequence underrepresentation predicts that replication intermediates should populate regions of DNA between fully polytenized euchromatic sequences and underpolytenized heterochromatic sequences. We directly tested this prediction using Dp1187, a 1300 kb Drosophila minichromosome containing well-defined heterochromatic regions. DNA from a euchromatic/heterochromatic junction region of Dp1187, demonstrating a significant gradient of underrepresentation in larval salivary glands, lacked the stalled replication forks predicted by the underreplication model. We consider an alternative mechanism leading to heterochromatic sequence underrepresentation involving a process of DNA elimination.


Salivary Gland Alternative Mechanism Dramatic Reduction Replication Fork Chromosome Structure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • Robert L. Glaser
    • 1
  • Gary H. Karpen
    • 1
  • Allan C. Spradling
    • 1
  1. 1.Howard Hughes Medical Institute Research LaboratoriesCarnegie Institution of WashingtonBaltimoreUSA

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