An analysis of meiotic impairment and of sex chromosome associations throughout meiosis in XYY mice

The existing XYY meiotic data for mice present a very heterogeneous picture with respect to the relative frequencies of different sex chromosome assoc iations, both at pachytene and diakinesis/metaphase I. Furthermore, where b oth pachytene and diakinesis/MI data are available for the same males, the frequencies of the different configurations at the two stages are very diff erent. In the present paper we utilise "XYY" and "XY/XYY" mosaic mice with cytologically distinguishable Y chromosomes to investigate the factors resp onsible for this heterogeneity between different males and between the two meiotic stages. It is concluded (1) that the initial pattern of synapsis is driven by the relatedness of the three pseudoautosomal regions (PARs); (?) that the order and extent of PAR synapsis within radial trivalents are als o affected by PAR relatedness and that this leads to chiasmata being prefer entially formed between closely related PARs; (3) that trivalents with a si ngle chiasma resolve into a bivalent + univalent by the diakinesis stage; ( 4) that although many spermatocytes with asynapsed sex chromosomes are elim inated between pachytene and diakinesis, those that survive this phase of e limination progress to the first meiotic metaphase (MI) and accumulate in l arge numbers, leading to an over-representation of those with univalents as compared to radial trivalents; and (5) that the arrested MI cells are even tually eliminated, so that very few "XYY" cells contribute products to MII. Copyright(C)2000S.KargerAG,Basel.