Therman E, Trunca C, Kuhn E M, Sarto G E
Hum Genet. 1986 Mar;72(3):191-5. doi: 10.1007/BF00291876.
The origin and behavior of human dicentric chromosomes are reviewed. Most dicentrics between two nonhomologous or two homologous chromosomes (isodicentrics), which are permanent members of a chromosome complement, probably originate from segregation of an adjacent quadriradial; such configurations are the result of a chromatid translocation between two nonhomologous chromosomes, or they represent an adjacent counterpart of a mitotic chiasma. The segregation of such a quadriradial may also give rise to a cell line monosomic for the chromosome concerned (e.g., a 45, X line). Contrary to the generally held opinion, isodicentrics rarely result from an isolocal break in two chromatids followed by rejoining of sister chromatids. In this case the daughter centromeres go to opposite poles in the next anaphase, and the resulting bridge breaks at a random point. This mechanism, therefore, leads to the formation of an isodicentric chromosome only if the two centromeres are close together, or if one centromere is immediately inactivated. Observations on the origin of dicentrics in Bloom syndrome support these conclusions. One centromere is permanently inactivated in most dicentric chromosomes, and even when the dicentric breaks into two chromosomes, the centromere is not reactivated. The appearance and behavior of the "acentric" X chromosomes show that their centromeres are similarly inactivated and not prematurely divided. Two Bloom syndrome lymphocytes, one with an extra chromosome 2 and the other with an extra chromosome 7, each having an inactivated centromere, show that this can also happen in monocentric autosomes.
本文综述了人类双着丝粒染色体的起源和行为。两个非同源或两个同源染色体之间的大多数双着丝粒染色体（等臂双着丝粒染色体）是染色体组的永久成员，可能起源于相邻四射体的分离；这种构型是两个非同源染色体之间染色单体易位的结果，或者它们代表有丝分裂交叉的相邻对应物。这种四射体的分离也可能产生与相关染色体单体的细胞系（例如，45,X细胞系）。与普遍观点相反，等臂双着丝粒染色体很少由两条染色单体的局部断裂后姐妹染色单体重新连接产生。在这种情况下，子着丝粒在下一个后期移向相反的极，并且产生的桥在随机点断裂。因此，只有当两个着丝粒靠得很近，或者一个着丝粒立即失活时，这种机制才会导致等臂双着丝粒染色体的形成。对布卢姆综合征中双着丝粒染色体起源的观察支持了这些结论。在大多数双着丝粒染色体中，一个着丝粒永久失活，即使双着丝粒染色体断裂成两条染色体，着丝粒也不会重新激活。“无着丝粒”X染色体的出现和行为表明它们的着丝粒同样失活且不会过早分裂。两个布卢姆综合征淋巴细胞，一个有额外的2号染色体，另一个有额外的7号染色体，每个都有一个失活的着丝粒，这表明这种情况也可能发生在单着丝粒常染色体中。
