title: X-ray-induced simple, pseudosimple and complex exchanges involving two distinctly painted chromosomes.
abstract: OBJECTIVE
  To detect simple, pseudosimple and complex chromosome exchanges in X-ray-induced aberrations involving two distinctly painted chromosomes. Each visibly complex two-paint exchange was analysed to determine the number of breaks and chromosomes necessary to derive the pattern. In addition, the number of associated paint junctions was scored to assess the frequency of non-reciprocal exchanges.
  
  
  METHODS
  Metaphase spreads were prepared from a human primary fibroblast cell line irradiated with 2, 4 and 6 Gy 250kV X-rays. FISH-painting was performed with distinctly labelled probes for chromosomes 1 and 2, and a pancentromeric probe.
  
  
  RESULTS
  From a total of 78 two-paint exchanges observed, 35 were apparently simple, with no additional counterstain chromatin, and 43 were visibly complex with two-colour painting, of which 23 contained at least one pseudosimple exchange. A detailed analysis of the number of two-paint colour junctions showed that at least 50% of the visibly complex exchange patterns involved non-reciprocal exchanges. The simple and complex exchange dose-response curves were considered to be linear and curvilinear respectively.
  
  
  CONCLUSIONS
  The frequency of non-reciprocal rejoining events within complex exchanges is consistent with an interaction model based on the free exchange of multiple break-ends. In addition, the simple and complex exchanges have distinct dose-response curves, in agreement with previous data for single-painted exchanges corrected for pseudosimples.
authors.affiliation: Medical Research Council, Radiation and Genome Stability Unit, Harwell, Chilton, UK. p.simpson@har.mrc.ac.uk
authors.forename: P J
authors.initials: PJ
authors.lastname: Simpson
authors.forename: D G
authors.initials: DG
authors.lastname: Papworth
authors.forename: J R
authors.initials: JR
authors.lastname: Savage
mesh_terms: D019457:Chromosome Breakage; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects*; D005456:Fluorescent Dyes; D006801:Humans; D014965:X-Rays