During development of the embryo it goes from being a single cell, the fertilized egg, to being a multi-cellular organism with billions of cells in it.

胚胎的发育,始于一个单一细胞,即受精卵,直到形成一个以十亿计数量的细胞构成的,多细胞有机体

耶鲁公开课 - 生物医学工程探索课程节选

All of the cells that are reproduced during development are the same in certain ways, they contain the same DNA, they're all progeny of the same fertilized egg, but differences are acquired within specific cell populations during the process of development.

所有在发育过程中繁殖的细胞,在某些方面都是一样的,它们都有相同的DNA,都是同一个受精卵的后代,但是分化是在特定细胞类群,发育过程中必不可少的

耶鲁公开课 - 生物医学工程探索课程节选