Who will be Kaepernick's backup?

The San Francisco 49ers are a team that was already wealthy in draft picks for 2013, and got even moreso thanks to their trade of QB Alex Smith to the Kansas City Chiefs in exchange for the Chiefs' second-rounder (No. 34 overall). But the move also leaves them with a void in their QB stable: namely, who will now be the backup to starter Colin Kaepernick?