Sun Fei, Oliver-Bonet M, Liehr T, Starke H, Turek P, Ko E, Rademaker A, Martin R H
Department of Medical Genetics, University of Calgary, Alberta, Canada.
Hum Reprod. 2006 Sep;21(9):2335-9. doi: 10.1093/humrep/del190. Epub 2006 Jun 3.
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.
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).
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).
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.
没有重组位点的二价体（可能是无交叉二价体）无法在中期板上正确定向，也无法将染色体分离到子细胞中。已知非交叉二价体会导致多种生物体的减数分裂停滞。
在来自10名正常男性睾丸活检的886个粗线期细胞（19492个二价体）中鉴定出单个非交叉二价体。采用荧光染色结合着丝粒特异性多色荧光原位杂交（cenM-FISH）技术，沿着每个二价体联会复合体（SC）鉴定人类MutL同源物1（MLH1）重组位点的错配修复基因突变。
共发现60个常染色体非交叉二价体（没有MLH1位点的SC），其中，21号染色体（2.1%）和22号染色体（1.7%）的比例显著高于11、12、19号染色体（各为0.1%）、13号染色体（0.2%）、14号染色体（0.6%）、16号染色体（0.5%）以及15、17、18、20号染色体（各为0.3%）（P<0.05）。性染色体单价体的频率为27%，高于任何常染色体二价体（P<0.0001）。
这些结果表明，G组染色体和性染色体最易出现没有重组位点的情况，因此在精子发生过程中更易发生不分离。这与先前精子核型分析和FISH分析的观察结果一致，这些结果表明，与其他常染色体相比，21号和22号染色体以及性染色体的非整倍体频率显著增加。
