title: Chromosome breakage and rejoining of sister chromatids in Bloom's syndrome.
abstract: The occurrence of chromosome breaks and reunion of sister chromatids in lymphocytes of two patients with Bloom's syndrome has been compared with those found in X-rayed and control cells. The distribution of breaks in BS is non-random both between and within chromosomes, the centric regions of certain chromosomes being preferentially involved. The following working hypotheses are put forward: When chromosome breaks in human lymphocytes occur in G0-G1, practically no sister chromatid reunion (SCR) takes place, whereas ends created by an S-G2 break show a considerable tendency to SCR. We propose further that chromosome aberrations in BS mainly result from breaks in S-G2, including possible U-type rejoining of sister chromatid exchanges. Fragments extra to an intact chromosome complement result from a chromatid break or an asymmetrical chromatid translocation in a previous mitosis.
mesh_terms: D002478:Cells, Cultured; D002869:Chromosome Aberrations; D003434:Crossing Over, Genetic; D004392:Dwarfism / Q000235:genetics*; D006801:Humans; D007621:Karyotyping; D008214:Lymphocytes / Q000648:ultrastructure; D010787:Photosensitivity Disorders / Q000235:genetics*; D012854:Sister Chromatid Exchange; D013577:Syndrome; D013684:Telangiectasis / Q000235:genetics*