Birchler James A, Han Fangpu
Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211
State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Plant Cell. 2018 Apr;30(4):771-779. doi: 10.1105/tpc.17.00989. Epub 2018 Mar 15.
Two obscure studies on chromosomal behavior by Barbara McClintock are revisited in light of subsequent studies and evolutionary genomics of chromosome number reduction. The phenomenon of deficiency recovery in which adjacent genetic markers lost in the zygote reappear in later developmental sectors is discussed in light of de novo centromere formation on chromosomal fragments. Second, McClintock described a small chromosome, which she postulated carried an "X component," that fostered specific types of chromosomal rearrangements mainly involving centromere changes and attachments to the termini of chromosomes. These findings are cast in the context of subsequent studies on centromere misdivision, the tendency of broken fragments to join chromosome ends, and the realization from genomic sequences that nested chromosomal insertion and end-to-end chromosomal fusions are common features of karyotype evolution. Together, these results suggest a synthesis that centromere breaks, inactivation, and de novo formation together with telomeres-acting under some circumstances as double-strand DNA breaks that join with others-is the underlying basis of these chromosomal phenomena.
结合后续研究以及染色体数目减少的进化基因组学,重新审视了芭芭拉·麦克林托克关于染色体行为的两项鲜为人知的研究。根据染色体片段上从头形成着丝粒的情况,讨论了缺失恢复现象,即在合子中丢失的相邻遗传标记在后期发育区段重新出现。其次,麦克林托克描述了一条小染色体,她推测该染色体携带一个“X成分”,它促进了特定类型的染色体重排,主要涉及着丝粒变化和与染色体末端的连接。这些发现是在后续关于着丝粒错误分裂、断裂片段连接染色体末端的趋势以及从基因组序列中认识到嵌套染色体插入和端对端染色体融合是核型进化的常见特征的背景下得出的。综合来看,这些结果表明,着丝粒断裂、失活和从头形成,以及端粒在某些情况下作为与其他双链DNA断裂连接的双链DNA断裂起作用,是这些染色体现象的潜在基础。