Neither is necessarily the case. If you can give any credence to rumors repeated over the years, there have reportedly been several instances when actresses were among the candidates considered for a new regeneration of the Doctor; and if I'm not mistaken, there was a borderline-canon (wrong side of the border, but still...) Doctor Who story done for some charity function that featured a female Doctor.

So a female Professor isn't necessarily going to be a radical change in the nature of the character.

-- Bob
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My race is pacifist and does not believe in war. We kill only out of personal spite.