title: Analysis of non-crossover bivalents in pachytene cells from 10 normal men.
abstract: BACKGROUND
  Bivalents with no recombination foci (possible achiasmates) are unable to orient properly on the metaphase plate or to segregate chromosomes to daughter cells. Non-crossover bivalents are known to cause meiotic arrest in various organisms.
  
  
  METHODS
  Individual non-crossover bivalents were identified in 886 pachytene cells (19 492 bivalents) from testicular biopsies of 10 normal men. Fluorescence staining combined with centromere-specific multicolour fluorescence in situ hybridization (cenM-FISH) was used to identify mismatch repair gene mutation of human mutL homologue 1 (MLH1) recombination foci along each bivalent synaptonemal complex (SC).
  
  
  RESULTS
  A total of 60 autosomal non-crossovers (SCs without an MLH1 focus) were found, and of these, chromosomes 21 (2.1%) and 22 (1.7%) had a significantly higher proportion than chromosomes 11, 12, 19 (each 0.1%), 13 (0.2%), 14 (0.6%), 16 (0.5%) and 15, 17, 18, 20 (each 0.3%) (P < 0.05). Sex chromosome univalents had a frequency of 27%, higher than that observed in any autosomal bivalent (P < 0.0001).
  
  
  CONCLUSIONS
  These results suggest that G-group chromosomes and sex chromosomes are most susceptible to having no recombination foci and thus would be more susceptible to non-disjunction during spermatogenesis. This is consistent with previous observations from sperm karyotyping and FISH analysis, which demonstrate that chromosomes 21 and 22 and the sex chromosomes have a significantly increased frequency of aneuploidy compared with other autosomes.
authors.affiliation: Department of Medical Genetics, University of Calgary, Alberta, Canada.
authors.forename: Fei
authors.initials: F
authors.lastname: Sun
authors.forename: M
authors.initials: M
authors.lastname: Oliver-Bonet
authors.forename: T
authors.initials: T
authors.lastname: Liehr
authors.forename: H
authors.initials: H
authors.lastname: Starke
authors.forename: P
authors.initials: P
authors.lastname: Turek
authors.forename: E
authors.initials: E
authors.lastname: Ko
authors.forename: A
authors.initials: A
authors.lastname: Rademaker
authors.forename: R H
authors.initials: RH
authors.lastname: Martin
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000782:Aneuploidy; D001706:Biopsy; D002891:Chromosomes, Human, Pair 21; D002892:Chromosomes, Human, Pair 22; D003434:Crossing Over, Genetic; D004252:DNA Mutational Analysis; D004260:DNA Repair; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D008875:Middle Aged; D009154:Mutation; D011995:Recombination, Genetic; D012730:Sex Chromosomes; D013091:Spermatogenesis; D013737:Testis / Q000473:pathology