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Non-random asynchronous replication at 22q11.2 favours unequal meiotic crossovers leading to the human 22q11.2 deletion
  1. A Baumer*,
  2. M Riegel*,
  3. A Schinzel
  1. Institute of Medical Genetics, University of Zurich, Schwerzenbach, Switzerland
  1. Correspondence to:
 Dr A Baumer
 Institute of Medical Genetics, University of Zurich, Schorenstrasse 16, CH-8603 Schwerzenbach, Switzerland;


Background: Analyses of the replication timing at 22q11.2 were prompted by our finding of a statistically significant bias in the origin of the regions flanking the deletion site in patients with 22q11.2 deletions, the proximal region being in the majority of cases of grandmaternal origin. We hypothesised that asynchronous replication may be involved in the formation of the 22q11.2 deletion, the most frequently occurring interstitial deletion in humans, by favouring the mispairing of low-copy repeats.

Methods: Replication timing during S phase at 22q11.2 was investigated by fluorescent in situ hybridisation on interphase nuclei. We report on the detection of non-random asynchronous replication at the human chromosome region 22q11.2, an autosomal locus believed not to contain imprinted genes.

Results: Asynchronous replication at 22q11.2 was observed without exception in all 20 tested individuals; these comprised individuals with structurally normal chromosomes 22 (10 cases), individuals with translocations involving the locus 22q11.2 (eight cases), and patients with a 22q11.2 deletion (two cases). The non-random nature of the asynchronous replication was observed in all individuals for whom the chromosomes 22 were distinguishable. The earlier replicating allele was found to be of paternal origin in all cases where the parental origin of the translocation or deletion was known.

  • human chromosome region 22q11.2
  • meiotic recombination
  • mode of formation of the 22q11.2 deletion
  • non-random asynchronous replication
  • LCR, low-copy repeats
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  • This study was supported in part by the Swiss National Foundation (grant numbers: 3100-056956.99 and 32-56051.98).

  • Conflict of interest: none declared.

  • * The authors AB and MR contributed equally to this work.

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