Sugawara S, Mikamo K
Cytogenet Cell Genet. 1983;35(1):34-40. doi: 10.1159/000131833.
The effects of maternal aging on the configuration of chiasmata, formation of univalents, and segregation of first meiotic (MI) chromosomes were investigated in young (5-8 mo) and old (16-19 mo) Chinese hamsters. Primary oocytes were collected only from mature follicles approximately 10 h before ovulation, and secondary oocytes were obtained from the oviducts 5 h after spontaneous ovulation. The average number of chiasmata per oocyte was significantly smaller in aged hamsters than in the young hamsters (P less than 0.001). Terminal chiasmata were found more frequently in the former group than in the latter one (P less than 0.001). These results coincided well with findings in the mouse. Since the 11 meiotic chromosomes could be divided into four morphologically distinguishable subgroups, it was possible to determine whether the same bivalent forming univalents at MI actually underwent nondisjunction in the following meiotic division. The incidence of both MI oocytes with a univalent pair and aneuploid MII oocytes due to first meiotic nondisjunction was significantly higher in the aged group than in the young group (P less than 0.01) and P less than 0.05, respectively). However, univalents occurred almost exclusively in the smallest metacentric chromosome group (96%), whereas nondisjunction took place nearly equally in each chromosomal subgroup. These results clearly showed that there was no correlation between the univalents seen at MI and nondisjunction during the first meiotic division.
研究了年轻（5 - 8月龄）和年老（16 - 19月龄）中国仓鼠母体衰老对交叉构型、单价体形成以及第一次减数分裂（MI）染色体分离的影响。仅在排卵前约10小时从成熟卵泡中收集初级卵母细胞，并在自发排卵后5小时从输卵管中获取次级卵母细胞。老年仓鼠每个卵母细胞的交叉平均数明显少于年轻仓鼠（P < 0.001）。前一组中末端交叉出现的频率高于后一组（P < 0.001）。这些结果与在小鼠中的发现非常吻合。由于11条减数分裂染色体可分为四个形态上可区分的亚组，因此有可能确定在MI形成单价体的同一二价体在随后的减数分裂中是否实际发生了不分离。老年组中具有一对单价体的MI卵母细胞和由于第一次减数分裂不分离导致的非整倍体MII卵母细胞的发生率分别显著高于年轻组（P < 0.01）和P < 0.05）。然而，单价体几乎只出现在最小的中着丝粒染色体组中（96%），而不分离在每个染色体亚组中发生的几率几乎相同。这些结果清楚地表明，在MI观察到的单价体与第一次减数分裂期间的不分离之间没有相关性。
