Analysis of recombination along chromosome 21 during human female pachytene stage.

It is accepted that recombination errors during human female meiotic prophasehave some influence on the origin of trisomy21. A total of 335 oocytes from four euploid fetuses were analysed by immunofluorescence and fluorescencein- situ hybridizationin order to assess the recombination nodulesalong chromosome 21. Results based on the analysis of recombination points on the bivalent 21 during human female meiosis showed that both number [none (3.70%), one (79.01%) and two (17.29%)] and distribution (always positioned interstitially on the q-arm) are different in males, ensuring that the two homologues more efficiently remain together until anaphaseI. Therefore, the mainly maternal origin of trisomy21 appears not be linked to the first stages of oocyte development during fetal life, and this leads to the suggestion that the influence of environmental factors on the segregation of chromosome 21homologues in later meiotic stages could have a significant role in the predominant maternal origin of trisomy21.