Imai H T
National Institute of Genetics, Shizuoka-ken, Japan.
Jpn J Genet. 1991 Oct;66(5):635-61. doi: 10.1266/jjg.66.635.
A quantitative analysis of the alterations of constitutive heterochromatin in eukaryotic chromosomal evolution was attempted using the accumulated C-banding data available for mammals, amphibians, fish, ants, grasshoppers, and plants. It was found that these eukaryotes could be classified into two types by their C-banding patterns: 1) Type I included mammals, fish, and ants, and 2) Type II included amphibians, grasshoppers, and plants. C-bands were rather scarce in Type I eukaryote chromosomes and were found around the pericentromeric region when present at all, whereas the predominance of interstitial or terminal C-bands was found in Type II eukaryote chromosomes. The Type I and II C-banding patterns can best be interpreted by assuming that in the former group of eukaryotes the saltatory increase in constitutive heterochromatin occurs preferentially at the pericentromeric regions of telocentric chromosomes induced by centric fission, with C-bands being eliminated almost completely by centric fusion and/or pericentric inversion. On the other hand, C-bands appear in the Type II eukaryotes both interstitially and in the telomeric regions of chromosomes, and there may be no effective mechanism to eliminate these bands once they are integrated.
利用哺乳动物、两栖动物、鱼类、蚂蚁、蚱蜢和植物已积累的C带数据，尝试对真核生物染色体进化中组成型异染色质的变化进行定量分析。结果发现，这些真核生物可根据其C带模式分为两类：1）I型包括哺乳动物、鱼类和蚂蚁；2）II型包括两栖动物、蚱蜢和植物。I型真核生物染色体中的C带相当稀少，若有C带，则仅见于着丝粒周围区域；而II型真核生物染色体中则以居间或末端C带为主。I型和II型C带模式的最佳解释是，在前一组真核生物中，组成型异染色质的跳跃式增加优先发生在由着丝粒分裂诱导的端着丝粒染色体的着丝粒周围区域，C带几乎完全因着丝粒融合和/或臂间倒位而消除。另一方面，C带出现在II型真核生物染色体的居间区域和端粒区域，一旦整合，可能没有有效的机制来消除这些带。
