Cytogenetic analysis of the paternal sex ratio chromosome of Nasonia vitripennis

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Paternal sex ratio (PSR) is a B chromosome found in the parasitic wasp Nasonia vitripennis. PSR has a unique etiology in that it destroys the paternal chromosomes of fertilized eggs, resulting in the production of all male families. This study examined structural aspects of PSR including size, C-banding, and silver staining. PSR was found to constitute approximately 5.7% of the genome of carrier males. C-banding confirmed the heterochromatic nature of PSR and the data suggest that PSR remains primarily condensed throughout the cell cycle. Examination of prometaphase spermatocytes revealed a secondary constriction on PSR. The constriction, however, did not stain positive for nucleolus organizer activity. During mitosis, PSR and the pericentromeric regions of the A chromosomes displayed a temporal pattern of silver staining, involving dense precipitation of silver prior to metaphase. This reaction is indicative of a protein complex specific to the heterochromatin of these regions. The implications of these findings to the origin of PSR are discussed.

Original languageEnglish (US)
Pages (from-to)157-161
Number of pages5
Issue number1
StatePublished - 1993
Externally publishedYes


  • B chromosome
  • Nasonia vitripennis
  • heterochromatin
  • nucleolus organizer region
  • paternal sex ratio


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