doctor mother brother的O哪个发音不同,tiger和doctor发音相同吗

her英[hə(r)]美[hɚ,ɚ,hɚr]brother英[ˈbrʌðə(r)]美[ˈbrʌðɚ]doctor英[ˈdɒktə(r)]美[ˈdɑ:ktə(r)

]mother英[ˈmʌðə(r)]美[ˈmʌðɚ]doctor有区别。