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

耶鲁公开课 - 生物医学工程探索课程节选

You can use PCR for fingerprinting as well, for looking in some unknown fluid for example, is a gene that I'm interested in there?

也可以用PCR做生物指纹鉴定,比如在一个未知溶液样本中,里面是不是有我感兴趣的那段基因呢

耶鲁公开课 - 生物医学工程探索课程节选

You can also use PCR to identify specific genes that are present in a biological sample.

你也可以利用PCR技术去识别,一个生物样本中的某段特定基因

耶鲁公开课 - 生物医学工程探索课程节选