Fertilization of these two where these two cells join occurs in the distal part of the fallopian tube.

受精的过程,就是这两种细胞,在输卵管壶腹部相互结合

耶鲁公开课 - 生物医学工程探索课程节选

That difference could have been generated during the process of fertilization.

这样的差异可能就发生在,受精的过程中

耶鲁公开课 - 生物医学工程探索课程节选