I'll start with a simple example of

先从一个简单例子着手
how one can detect a gene in a fluid,

如何在一个血样中
in a blood sample for example,

侦测是否存在某段基因序列
where that gene is unknown.

某段未知基因序列
This takes advantage of the very specific properties of restriction enzymes.

这利用了限制酶的独特性质
This particular example involves the gene for sickle cell anemia.

本例子中就包括镰状红细胞贫血症的基因
Sickle cell anemia is a disease

镰状红细胞贫血症
that affects a subset of the population.

是一种作用于特定人群的疾病
It's a single gene defect

是一种单基因缺陷
and we know exactly

而且我们准确地知道
where the genetic defect is in sickle cell.

镰状红细胞贫血的基因缺陷在哪里
It's on the gene for hemoglobin and the hemoglobin that you produce

这个缺陷基因和血红蛋白有关