Are Alex Trebek's answers recorded

Alex Trebek asked questions that are written and sometimes offers more information. A link under related links records some of what he says

During the game, Alex might mention a tidbit or two on various clues. This is usually information that has been written on his copy of the game material by one of the writers or researchers to add a little something extra to the game and for the people watching. There is also additional information written on the copies of the game material pertaining to any alternate correct responses that might be given by a contestant. This is usually something that might have come up in the meetings that Alex has with the producers and writers before the games are to be played.

There may be some clues that come up in the game where the clue crew or a celebrity may read a clue that is prerecorded, Alex has a note written on his sheet indicating that it is a video clue.