The genome starts piling on mutations that mean nothing; that's how they date the branches of the genome, by looking at the number of neutral mutations.

基因积累了许多无意义的突变,这就是他们如何鉴定基因分支的年代,看中性突变的数量就行了

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You could use PCR to do that because if you amplify a gene in PCR, that gene had to be present from the beginning.

你可以用PCR技术来鉴定,因为如果你能用PCR扩增某一段基因,说明它从一开始就肯定是存在的

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