Puro J
Department of Biology, University of Turku, Finland.
Chromosoma. 1991 Jun;100(5):305-14. doi: 10.1007/BF00360529.
In tricomplex heterozygotes in Drosophila melanogaster three metacentric autosomes (the TRI chromosomes) appear as a trivalent in meiosis while one autosome consisting of two homologous arms attached to the same centromere (a compound) behaves as an obligatory univalent. Cytological analysis of meiosis of tri-complex heterozygotes indicates that in oocytes the univalent compound behaves non-independently in relation to segregation of the trivalent. The compound is distributed preferentially to the same pole as one TRI chromosome. In spermatocytes the compound is distributed at random. In some oocytes the directed segregation is shown to be due to a disjunctional interaction between the compound and one partner of the trivalent at the same time as the other two chromosomes of the trivalent are separating from each other. The basic difference between the segregational mechanisms in the two sexes is discussed with a review of evidence indicating that in males segregation is determined by physical linkage that produces a stable orientation of the homologues at metaphase I. On the other hand, both genetic and cytological evidence indicate that in females a physical linkage (a chiasma) is non-essential for maintenance of co-orientation and stability after the onset of prometaphase. Genetic and cytological evidence support the hypothesis that disjunction is predetermined by non-random arrangement of the centromeric regions of chromosomes in the chromocentre - a suprachromosomal organization characteristic of maturing oocytes.
在黑腹果蝇的三复合体杂合子中，三条中着丝粒常染色体（TRI染色体）在减数分裂时呈现为一个三价体，而一条由附着于同一着丝粒的两条同源臂组成的常染色体（复合染色体）则表现为一个 obligatory 单价体。对三复合体杂合子减数分裂的细胞学分析表明，在卵母细胞中，单价复合染色体在三价体分离方面表现出非独立行为。该复合染色体优先与一条TRI染色体分配到同一极。在精母细胞中，复合染色体随机分配。在一些卵母细胞中，定向分离被证明是由于复合染色体与三价体的一个伙伴之间的分离相互作用，与此同时，三价体的另外两条染色体彼此分离。本文讨论了两性分离机制的基本差异，并回顾了相关证据，这些证据表明，在雄性中，分离由物理连锁决定，这种连锁在中期I产生同源染色体的稳定取向。另一方面，遗传和细胞学证据均表明，在雌性中，在前期开始后，物理连锁（交叉）对于维持共取向和稳定性并非必需。遗传和细胞学证据支持这样的假说，即分离由染色中心中染色体着丝粒区域的非随机排列预先决定，染色中心是成熟卵母细胞特有的超染色体组织。
