It evolved into what we call the mitochondrion.

它进化成了我们所说的线粒体。

As a fertilized egg grows and divides, those thousands of mitochondria are divvied up into the cells of the developing embryo.

着受卵的生长和分裂，这数以千计的线粒体被分配中的胚胎细胞中。

But a mitochondrion is a complex piece of machinery, and a lot can go wrong.

但是线粒体是一种复杂的机器，很多地方都可能出错。