These response pdf files are for my examiners for my PhD viva. During my PhD, I invetigated the functional roles of Rac1b in both mammary gland development and tumourigensis. It is demonstrated that Rac1b is dispensible for mammry gland development. Also, loss of Rac1b function increases chemosensitivity of primary breast tumour cells. Notably, this study elucidated that Rac1b might be a marker for a subpopulation of cancer stem cells through using a novel mouse model, generated by CRISPR method in my study.