You're not fishing through a whole chromosome in order to find what you want, but you're going to a cell that's already enriched in it.

你不是大海捞针地,在一整个染色体中找基因,而是在一个充满了,你感兴趣的基因的细胞里找

耶鲁公开课 - 生物医学工程探索课程节选

it's like finding a needle in a hay stack.

这简直是大海捞针。

It's like 课堂 - SpeakingMax英语口语达人