I bought Dragon Age Origins together with Awakening extension. Now when I started the game, I was given a choice whether I want to start with Dragon Age Origins or with Awakening. I chose Dragon Age Origins storyline, is there option for me to choose Keeper class during the game, or is it only once I start the extension storyline?

I bought Dragon Age: Origins together with the Awakening expansion. When I started the game, I was given a choice whether I want to start with Dragon Age: Origins or with Awakening. I chose the Dragon Age: Origins storyline; is there an option for me to choose the Keeper class during the game, or is it only once I start the expansion storyline?