The size of the cells could be different; maybe mitosis is asymmetrical in some way so that one of the cells ends up being bigger than the other.

细胞大小可能会不同,也许有丝分裂的过程是不对称的,致使子细胞一个大一个小

耶鲁公开课 - 生物医学工程探索课程节选

One result of this asymmetrical division is a committed progenitor cell.

这种不对称分裂的一个结果,是产生定向的祖细胞

耶鲁公开课 - 生物医学工程探索课程节选