That's one of the properties of mitosis, that the DNA gets completely duplicated during the S phase, during DNA synthesis phase.

有丝分裂的一个特征,就是DNA在S期内完全复制,S期就是DNA合成期

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That's synthesis and that has to happen in order for cells to replicate and cell replication is happening in your body all the time.

这个DNA合成过程是,细胞复制中不可或缺的部分,细胞复制时刻不停的在你身体里进行着

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What's shown here is what's called a replication fork in DNA that's undergoing synthesis.

这里展示的是在DNA合成过程中,形成的DNA复制叉

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