I've been a great fan of Dr Who ever since it started so I was saddened to read of the passing of these two very talented women especially after the passing of Elisabeth Sladen just over a year ago.
Caroline John played Dr Liz Shaw in 1970 opposite one of my favourite Doctors, Jon Pertwee. (The Pertwee link is a bit effusive but it has some interesting information about his career.) What I loved about Liz Shaw was that she was a highly qualified scientist whose function was much more than to be a damsel in distress who screamed a lot. Very much the Doctor's intellectual equal, she was also a member of Unit, the military unit set up to deal with unexplained events. I was very sorry she was written out after a relatively short time.
Mary Tamm played the Timelord, Romana, opposite Tom Baker before Romana regenerated and Mary Tamm was replaced by Lalla Ward. Romana was another intelligent, feisty, female companion. Beautiful, cool and very much in control, Mary Tamm's Romana didn't let the Doctor get away with doing whatever he wanted, something he was/is very fond of doing. She was another companion I was sorry to see go.
Both Caroline John and Mary Tamm went on to successful careers post Dr Who. They will be missed.