It evolved into what we call the mitochondrion.

它进化成了我们所说体。

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

随着受精卵和分裂，这数以千计体被分配到发育中胚胎细胞中。

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

但是体是一种复杂机器，很多地方都可能出错。