Lukaszewski Adam J
Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA.
Chromosoma. 2008 Dec;117(6):569-78. doi: 10.1007/s00412-008-0174-4. Epub 2008 Aug 5.
Distal location of chiasmata in chromosome arms is thought to be a consequence of the distal initiation of synapsis. Observations of meiotic behavior of a rye chromosome with an inverted arm show that patterns of chiasma distribution and frequency are also inverted; therefore, the patterns of synapsis and chiasma distribution are independent, and recombination frequency along a chromosome is position-independent and segment-specific. Since cases of random distribution of chiasmata and recombination are known in rye, a genetic mechanism must be present that licenses specific chromosome regions for recombination. Large differences in the metaphase I pairing of the inversion in various combinations of two armed and telocentric chromosomes confirm the major role of the telomere bouquet in early homologue recognition. However, occasional synapsis and chiasmate pairing of the distal regions of normal arms with the proximal regions of the inversion suggest that an alternative mechanism for juxtaposing of homologues must also be present. Synapsis in inversion heterozygotes was mostly complete but in the antiparallel orientation, hence defying homology, but non-homologues never synapsed. Instances of synapsis strictly limited to the chiasma-capable segments of the arm suggest that, in rye, both recombination-dependent and recombination-independent mechanisms for homologue recognition must be present.
着丝粒在染色体臂远端的位置被认为是联会远端起始的结果。对一条具有倒位臂的黑麦染色体减数分裂行为的观察表明，交叉分布和频率模式也发生了倒转；因此，联会和交叉分布模式是独立的，并且沿着染色体的重组频率与位置无关且具有片段特异性。由于在黑麦中已知交叉和重组的随机分布情况，所以必然存在一种遗传机制来许可特定染色体区域进行重组。在两臂染色体和端着丝粒染色体的各种组合中，中期I倒位配对的巨大差异证实了端粒花束在早期同源染色体识别中的主要作用。然而，正常臂的远端区域与倒位的近端区域偶尔会发生联会和交叉配对，这表明还必须存在一种使同源染色体并列的替代机制。倒位杂合子中的联会大多是完全的，但呈反平行方向，因此违背了同源性，但非同源染色体从不联会。严格局限于臂上有交叉能力片段的联会实例表明，在黑麦中，同源染色体识别必定存在依赖重组和不依赖重组的机制。
