The 12 Bar Blues in the key of A contains the chords A7 (I chord), D7 (IV chord) and E7 (V) chord. Below is the 12 Bar Blues starting on A7.
12 Bar Blues in A (Jazz Variation)
The Jazz variation of the 12 Bar Blues in A adds some extra chords. The 12 Bar Blues structure remains the same, but certain chords are substituted. For example, the A7 chord in the fourth bar is substituted with a Em7 moving to an A7 chord.