当流感病毒由一个人或一只鸟传给另一个人或鸟时，由于病毒复制错误，它们通常会带上基因中的随机变化。

As influenza viruses pass from one person, or bird, to another, they normally pick up random changes in their genes because of errors in viral replication.

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流感病毒在自身复制时通过一系列的复制错误也在不断的进行变异。

Flu viruses also mutate, by making mistakes when replicating.

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突变可以是由辐射、化学作用、外部病原体(如：病毒)或细胞分裂时基因组复制错误造成。

Mutations can be induced by radiation, chemical treatment, foreign pathogens (e.g. viruses), or due to errors that occur during replication of the genome each time a cell divides.

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