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replication timing
Replication timing refers to the order in which segments of DNA along the length of a chromosome are duplicated.
==DNA replication==
In eukaryotic cells (cells that package their DNA within a nucleus), chromosomes consist of very long linear double-stranded DNA molecules. During the S-phase of each cell cycle (Figure 1), all of the DNA in a cell is duplicated in order to provide one copy to each of the daughter cells after the next cell division. The process of duplicating DNA is called DNA replication, and it takes place by first unwinding the duplex DNA molecule, starting at many locations called DNA replication origins, followed by an unzipping process that unwinds the DNA as it is being copied. However, replication does not start at all the different origins at once. Rather, there is a defined temporal order in which these origins fire. Frequently a few adjacent origins open up to duplicate a segment of a chromosome, followed some time later by another group of origins opening up in an adjacent segment. Replication does not necessarily start at exactly the same origin sites every time, but the segments appear to replicate in the same temporal sequence regardless of exactly where within each segment replication starts. Figure 2 shows a cartoon of how this is generally envisioned to occur, while Figure 3 shows an animation of when different segments replicate in one type of human cell.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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