She dreamed of being a doctor and went to college to study medicine. But when Dawn discovered the drama club, she caught the acting bug and scuttled her ambition to become a doctor.
"I got what I call Joe Namath's knee and I couldn't take PE so I took acting and fell in love with it and changed my major."
Dawn moved to LA, got an agent and began making appearances in shows like "Bonanza" and "Maverick." She auditioned for "Gilligan" and beat out many actresses, including Raquel Welch, for the job. With Tina Louise already cast, perhaps the producers felt that the island wasn't big enough for two known sex symbols.
The pilot was filmed before Dawn came aboard, and once she was hired the Mary Ann and Professor (Russell Johnson) characters were omitted from the credits in the original theme song. They were referred to as "the rest."
Dawn learned years later that Bob Denver (Gilligan) had demanded that the studio executives add Dawn and Johnson to the opening credits.