Perkins D D, Raju N B, Barry E G, Butler D K
Department of Biological Sciences, Stanford University, California 94305-5020, USA.
Genetics. 1995 Nov;141(3):909-23. doi: 10.1093/genetics/141.3.909.
In approximately 3% of Neurospora crassa rearrangements, part of a chromosome arm becomes attached to the nucleolus organizer region (NOR) at one end of chromosome 2 (linkage group V). Investigations with one inversion and nine translocations of this type are reported here. They appear genetically to be nonreciprocal and terminal. When a rearrangement is heterozygous, about one-third of viable progeny are segmental aneuploids with the translocated segment present in two copies, one in normal position and one associated with the NOR. Duplications from many of the rearrangements are highly unstable, breaking down by loss of the NOR-attached segment to restore normal chromosome sequence. When most of the rearrangements are homozygous, attenuated strands can be seen extending through the unstained nucleolus at pachytene, joining the translocated distal segment to the remainder of chromosome 2. Although the rearrangements appear genetically to be nonreciprocal, molecular evidence shows that at least several of them are physically reciprocal, with a block of rDNA repeats translocated away from the NOR. Evidence that NOR-associated breakpoints are nonterminal is also provided by intercrosses between pairs of translocations that transfer different-length segments of the same donor-chromosome arm to the NOR.
在粗糙脉孢菌约3%的重排中，一条染色体臂的一部分会附着于2号染色体（连锁群V）一端的核仁组织区（NOR）。本文报道了对一种倒位和九种此类易位的研究。从遗传学角度看，它们似乎是非相互的且是末端的。当重排为杂合状态时，约三分之一的存活后代是部分非整倍体，其中易位片段有两份，一份处于正常位置，一份与NOR相连。许多重排产生的重复片段高度不稳定，会通过丢失与NOR相连的片段而分解，以恢复正常的染色体序列。当大多数重排为纯合状态时，在粗线期可见变细的链延伸穿过未染色的核仁，将易位的远端片段与2号染色体的其余部分相连。尽管从遗传学角度看重排似乎是非相互的，但分子证据表明其中至少有几种在物理上是相互的，即有一段rDNA重复序列从NOR处易位。将同一供体染色体臂不同长度片段转移到NOR的易位对之间的杂交也提供了NOR相关断点并非末端的证据。
