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染色体是真核细胞遗传信息的载体。在DNA合成期(S期)细胞内所有染色体都进行复制,因而S期后细胞内染色体数目均加倍,但此时经过复制的染色体还没有分离,仍借着丝粒连结在一起,直到有丝分裂后期,着丝粒分裂后,才由纺锤丝牵引分别进入两个子细胞。染色体完成复制后一直到有丝分裂期着丝粒分裂前这段时期内,由同一着丝粒连结在一起的两条子染色体就是一对姊妹染色单体。姊妹染色单体之间所进行的物质交换,即所谓姊妹染色单体交换(sister chromatid exchange,SCE)。
Chromosomes are carriers of genetic information for eukaryotic cells. In the DNA synthesis phase (S phase), all the chromosomes in the cell are replicated, so that the number of intracellular chromosomes doubles after S phase, but the replicated chromosomes have not yet been separated and are still linked together by the silk until the end of mitosis. After the centromere was split, it was pulled into the two daughter cells by spinning spindles. The two daughter chromosomes linked together by the same centromere are the pair of sister chromatids after the chromosomes have been replicated until the mitotic stage. Material exchanges between sister chromatids, the so-called sister chromatid exchange (SCE).